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Smoking History Intensity and Permanent Tooth Removal: Findings from a National United States SampleThe role of smoking in the development of periodontal disease has been well explored. However, this study aims to explore the relationship between intensity of smoking history and permanent tooth removal. We utilized the 2022 Behavioral Risk Factor Surveillance System (BRFSS), a nationally representative sample of 107,859 US adults, to explore this association. Smoking history intensity was a BRFSS-derived measure of pack-year smoking history. Permanent tooth removal was binarized as the presence or absence of a history of permanent tooth removal. A binary logistic regression was conducted to analyze this association after adjusting for a variety of sociodemographic, health, and substance-use covariates. There was a dose-dependent relationship in which increasing smoking history intensity was associated with increased odds for removal of one or more permanent teeth. For example, those who reported a pack-year history of 30 or more years had a 6.4 times significantly higher odds of reporting a history of permanent tooth removal when compared to those with a 0 pack-year history (adjusted odds ratio = 6.37, 95% CI = 3.80–10.69, p < 0.001). These findings can be used to promote smoking reduction or cessation as a means of decreasing risk of permanent tooth removal due to tooth decay or gum disease.
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The Bok-IP3R interaction and the impact it has on apoptosis, Bok stability, and IP3R-mediated calcium mobilizationBcl-2-related ovarian killer, Bok, is often considered a pro-apoptotic Bcl-2 family member due to its ability to induce mitochondrial outer membrane permeabilization (MOMP) when over-expressed. However, there are many conflicting reports regarding endogenous Bok's apoptotic function and stability. Some studies claim that endogenous Bok is constitutively a MOMP-mediator but is very unstable and kept at very low levels via ubiquitin proteasome pathway (UPP)-mediated degradation. On the other hand, many studies, including those from the Wojcikiewicz Lab, indicate that endogenous Bok is a stable protein constitutively bound to inositol 1,4,5-trisphosphate receptors (IP3Rs), a calcium (Ca2+) release channel in the endoplasmic reticulum (ER) membrane, where it would be unable to induce MOMP. In fact, Bok KO mice have no developmental of phenotypical abnormalities, further suggesting that Bok's "killer" characterization needs to be reconsidered. Since endogenous Bok is an ER protein, studying its MOMP-like properties seems futile. Therefore, focusing on the significance of the Bok-IP3R interaction has been the priority of the Wojcikiewicz Lab since we discovered the complex. Over the years, we found that Bok protects IP3Rs from proteolytic cleavage and that Bok stability is dependent on its ability to bind to IP3Rs. However, surprisingly, there is no clear evidence to date that Bok influences the Ca2+ mobilizing activity of IP3Rs. Here, I study in detail the Bok-IP3R interaction and the impact it has on apoptosis, Bok stability, and IP3R-mediated Ca2+ mobilization. I resolve the controversy surrounding the apoptotic function of exogenous and endogenous Bok and hypothesize why there is a discrepancy between the two. Also, I show that IP3R binding in the ER membrane is essential for Bok stability, and without them Bok is rapidly degraded by the UPP. This demonstrates that the Bok-IP3R interaction is critical to Bok function, likely including its newly emerged non-apoptotic roles, such as regulating mitochondrial dynamics and mitochondria associated-ER membranes. Finally, for the first time, I reveal that Bok has suppressive effects on IP3R-mediated Ca2+ mobilization and describe how these effects are reversed when Bok is phosphorylated at serine-8. Overall, this thesis demonstrates the importance of the Bok-IP3R interaction on both Bok and IP3R function.
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Diverging cognitive benefits from education between rural and urban middle-aged and older adults in the USA.Subjective cognitive decline (SCD) is defined as self-reported increase in confusion or memory loss. There is limited research on the interplay between rural-urban residence and education on SCD.
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Longitudinal Engagement in Modifiable Lifestyle Behaviors and Racial–Ethnic Differences in Dementia RiskObjectives The objective was to examine racial–ethnic differences in longitudinal engagement for lifestyle behaviors and moderating role of race–ethnicity between lifestyle behaviors and dementia risk. Methods We analyzed 2011–2021 National Health and Aging Trends Study data, a nationally representative U.S. sample of 6155 White, Black, Hispanic, and Asian older adults aged 65+. Cox models regressed dementia on the interaction between lifestyle behaviors (physical activity, smoking, and social contacts) and race–ethnicity. Results Only smoking was associated with about a 45% higher dementia risk (aHR = 1.45, 95% CI = 1.11–1.89). On average, Black and Hispanic respondents exhibited less frequent physical activity and social contacts, along with more frequent smoking. There was one significant interaction; more social contacts were associated with lower dementia risk among Asian respondents (aHR = 0.16, 95% CI = 0.05–0.55). Discussion Racial–ethnic differences in lifestyle behaviors should be considered when addressing dementia disparities. Future research needs to explore the relationship between social contacts and lower dementia risk among Asian older adults.
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Sociodemographic Factors and Vulnerability to Multiple Extreme Weather Events: A National Study in the U.S.Background Millions of U.S. residents experience increasingly more prevalent weather events due to climate change, however, there is limited research exploring the vulnerability to multiple extreme weather events using a national U.S. sample. Aims Identify patterns in exposures to climate events, and examine sociodemographic factors associated with increased climate event vulnerability. Method Data was retrieved from the May 2022 American Trends Panel, a nationally representative sample of 10,282 United States adults. We performed a latent class analysis, a statistical method used to identify unobserved subgroups (latent classes) within a population, to group respondents by patterns in five climate event experiences (heatwave, intense storm, wildfire, drought, and sea level rise), and analyzed variables associated with vulnerability to climate events using weighted multinomial logistic regression, a statistical method that models the probability of membership in one of several outcome categories (climate vulnerability groups) relative to a reference category, while accounting for survey weights to ensure generalizability to the U.S. population. Results Respondents were categorized into four latent classes, which are unobserved subgroups identified through patterns in exposures to five climate events (heatwave, intense storm, wildfire, drought, and sea level rise). These subgroups were based on exposures to heatwave (42.5 %), intense storm (43.2 %), wildfire (21.3 %), drought (30.8 %) and sea level rise (15.8 %): high (9.8 %), heat-storm (22.2 %), heat-drought (13.4 %), and low (54.6 %) climate event vulnerability. Relative risk for high climate event vulnerability refers to the likelihood of belonging to the “high vulnerability” group compared to the “low vulnerability” group. It is assessed using the relative risk ratio (RRR), which is a measure of the association between a particular sociodemographic factor (e.g., age, gender, region) and the likelihood of being in a specific vulnerability group relative to the reference group. For instance, an RRR <1 indicates a reduced risk, while an RRR >1 indicates an increased risk compared to the reference category. Relative risk for high climate event vulnerability was lower for older adults (RRR = 0.39, p < 0.001), potentially reflecting a greater capacity to cope with certain climate events, such as access to stable housing or resources. However, this finding should not be interpreted as older adults being universally less vulnerable. Numerous studies have shown that older adults are at significantly higher risk during heatwaves due to physiological and social factors, which our analysis may not fully capture. Relative risk for high vulnerability was higher for females (RRR = 1.42, p = 0.01) and residents in the South (RRR = 2.05, p = 0.003) and West (RRR = 9.31, p < 0.001) geographic regions. Relative risk for heat-drought was higher for Hispanic adults (RRR = 1.51, p = 0.03), but lower for high school graduates (RRR = 0.40, p = 0.01) compared to those who did not complete high school. Conclusions We identified several underlying climate event exposure subpopulations, ranging from low to high vulnerability. As climate-related events become more frequent, our results provide critical insights for stakeholders to identify high-risk individuals and prioritize resources for disaster management.
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Sleep disturbances and racial-ethnic disparities in 10-year dementia risk among a national sample of older adults in the USARace/ethnicity and sleep disturbances are associated with dementia risk.
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Racial and ethnic disparities in social isolation and 11-year dementia risk among older adults in the United States.Social isolation has been implicated in the development of cognitive impairment, but research on this association remains limited among racial-ethnic minoritized populations. Our study examined the interplay between social isolation, race-ethnicity and dementia.
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Research on Health Topics Communicated through TikTok: A Systematic Review of the LiteratureTikTok has more than 1.5 billion users globally. Health and wellness content on the application increased by more than 600% in 2021. This systematic review seeks to summarize which fields within medicine have embraced researching health communication on the TikTok platform and the most common measures reported within this literature. Research questions include what categories of health topics on TikTok are investigated in the literature, trends in topics by year, and types of outcomes reported. Embase, CINAHL, Scopus, and Ovid MEDLINE databases were searched in March 2024. Eligible studies met four criteria: (1) investigated human health topics on TikTok; (2) conducted in the United States; (3) published in English; and (4) published in a peer-reviewed journal. Of the 101 included studies, 50.5% (N = 51) discussed non-surgical specialties, 9.9% (N = 10) discussed topics within surgery, and 11.9% (N = 12) discussed COVID-19. The number of papers referencing non-surgical topics spiked in 2023, and no increase was seen in the number of COVID-19 papers over time. Most papers reported a number of interactions, and papers about mental health were least likely to report accuracy. Our findings highlight several health topics with a wide breadth of research dedicated to them, such as dermatology and COVID-19, and highlight areas for future research, such as the intersection of cancer and TikTok. Findings may be influential in the fields of medicine and healthcare research by informing health policy and targeted prevention efforts. This review reveals the need for future policies that focus on the role and expectations of the healthcare worker in health communication on social media. Implications for clinical practice include the need for providers to consider an individual's perception of health and illness, given the wide variety of information available on social media applications such as TikTok. This review was pre-registered on PROSPERO (CRD42024529182).
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Role of Cytoreductive Nephrectomy in Metastatic Clear Cell Renal cell Carcinoma in the Era of immunotherapy: An Analysis of the National Cancer DatabaseBackground: The effectiveness of the clinical outcome of CN (Cytoreductive Nephrectomy) in cases of mccRCC (Metastatic Clear Cell Renal cell Carcinoma) is still uncertain despite two trials, SURTIME and CARMENA. These trials, conducted with Sunitinib as the standard treatment, did not provide evidence supporting the use of CN. Methods: We queried the NCDB for stage IV mccRCC patients between the years of 2004 to 2020, who received (immunotherapy) IO with or without nephrectomy. Overall survival (OS) was calculated among three groups of IO alone, IO followed by CN (IOCN), CN followed by IO (CNIO). Cox models compared OS by treatment group after adjusting for sociodemographic, health, and facility variables. Results: From 1,549,101 renal cancer cases, 7983 clear and nonclear cell renal cell carcinoma cases were identified. After adjusting for sociodemographic and health covariates, patients who received IO followed by CN or CN followed by IO had a respective 64% (adjusted Hazard Ratio [aHR] = 0.36, 95% CI = 0.30-0.43, P = .006] and 47% (aHR = 0.53, 95% CI = 0.49-0.56, P = .001) mortality risk reduction respectively compared to patients who received IO alone. Compared to White adults, individuals who identified as Black exhibited 17% higher risk mortality (aHR = 1.17, 95% CI = 1.06-1.30, P = .002). Patients who received CN prior to IO had a 59% associated mortality risk compared to patients who received IO followed by CN who had a lower risk, 35.7% (P < .001). Conclusions: Patients receiving CN regardless of sequence with IO did better than IO alone in this national registry-based adjusted analysis for mccRCC. Presently available data indicates that the combination of CN and IO holds promise for enhancing clinical results in patients with mRCC.
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Imbalanced specialty representation of USMLE and NBME test writersPurpose: The United States Medical Licensing Examination (USMLE) is an examination series required for allopathic physician licensure in the United States (US). USMLE content is created and maintained by the National Board of Medical Examinations (NBME). The specialty composition of the USMLE and NBME taskforce members involved in the creation of examination content is currently unknown. Methods: Using the 2021 USMLE and 2021 NBME Committees and Task Forces documents, we determined each member's board-certified primary specialty and involvement in test material development committees who we dubbed "test writers". Total active physicians by primary specialty were recorded from the 2020 Physician Specialty Data Report published by the Association of American Medical Colleges (AAMC). Descriptive statistics and chi-square analysis were used to analyze the cohorts. Results: The USMLE and NBME test writer primary specialty composition was found to be significantly different compared to the US active physician population (USMLE χ2 [32]=172, p<.001 and NBME χ2 [32]=200, p<.001). Only nineteen specialties were represented within USMLE test writers, with three specialties being proportionally represented. Two specialties were represented within NBME test writers. Obstetrics and Gynecology physicians were proportionally represented in USMLE but not within NBME test writers. Internal Medicine (IM) accounts for the largest percentage of all USMLE test writers (60/197, 30%) with an excess representation of 31 individuals. Conclusions: There is an imbalance in the specialty representation of USMLE and NBME test writers compared to the US active physician population. These findings may have implications for the unbiased and accurate portrayal of topics in such national examinations; thus, future investigation is warranted.
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Effectiveness of Artificial Intelligence Technologies in Cancer Treatment for Older Adults: A Systematic ReviewBackground: Aging is a multifaceted process that may lead to an increased risk of developing cancer. Artificial intelligence (AI) applications in clinical cancer research may optimize cancer treatments, improve patient care, and minimize risks, prompting AI to receive high levels of attention in clinical medicine. This systematic review aims to synthesize current articles about the effectiveness of artificial intelligence in cancer treatments for older adults. Methods: We conducted a systematic review by searching CINAHL, PsycINFO, and MEDLINE via EBSCO. We also conducted forward and backward hand searching for a comprehensive search. Eligible studies included a study population of older adults (60 and older) with cancer, used AI technology to treat cancer, and were published in a peer-reviewed journal in English. This study was registered on PROSPERO (CRD42024529270). Results: This systematic review identified seven articles focusing on lung, breast, and gastrointestinal cancers. They were predominantly conducted in the USA (42.9%), with others from India, China, and Germany. The measures of overall and progression-free survival, local control, and treatment plan concordance suggested that AI interventions were equally or less effective than standard care in treating older adult cancer patients. Conclusions: Despite promising initial findings, the utility of AI technologies in cancer treatment for older adults remains in its early stages, as further developments are necessary to enhance accuracy, consistency, and reliability for broader clinical use.
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Healthcare staff perceptions of an electronic hand hygiene monitoring system within a large university systemObjective: The acceptability of an electronic HH monitoring system (EHHMS) was evaluated among hospital staff members. Design: An electronic HH monitoring system was implemented in June 2020 at a large, academic medical center. An interdisciplinary team developed a cross-sectional survey to gather staff perceptions of the EHHMS. Setting: The survey was conducted at a public, tertiary acute care hospital. Participants: The survey included current employees and staff. 1,273 participants responded. The mean age was 44.9 years (SD = 13.5). Most of the samples were female (71%) and non-Hispanic white (83%). Methods: A survey was conducted between June and July 2021. Responses were analyzed using Stata statistical software. Multiple logistic regression models were constructed to examine factors associated with negative perceptions of the EHHMS and its radiofrequency identification (RFID) badge. Supporting qualitative analyses were performed using Atlas.ti version 9. Results: Three-quarters (75%) of respondents reported neutral to negative perceptions of the EHHMS and its associated badge. Respondents reported limited influence on HH practices. Age, campus location, length of employment, job role, and opinion on data sharing were associated with negative perceptions of the EHHMS and RFID badge. Position in a direct patient care role was associated with negative perceptions of the RFID badge. Conclusions: Perceptions of the EHHMS aligned with previous research. Identified associations provide opportunities for targeted education, outreach, and intervention to increase acceptability and uptake. Lack of acceptance is explained by poorly perceived ease of use and usefulness, as well as challenges in implementation.
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Pulse Pressure as a Hemodynamic Parameter in Preeclampsia with Severe Features Accompanied by Fetal Growth RestrictionBackground: Modern management of preeclampsia can be optimized by tailoring the targeted treatment of hypertension to an individual's hemodynamic profile. Growing evidence suggests different phenotypes of preeclampsia, including those with a hyperdynamic profile and those complicated by uteroplacental insufficiency. Fetal growth restriction (FGR) is believed to be a result of uteroplacental insufficiency. There is a paucity of research examining the characteristics of patients with severe preeclampsia who do and who do not develop FGR.We aimed to elucidate which hemodynamic parameters differed between these two groups. Methods: All patients admitted to a single referral center with severe preeclampsia were identified. Patients were included if they had a live birth at 23 weeks of gestation or higher. Multiple gestations and pregnancies complicated by fetal congenital anomalies and/or HELLP syndrome were excluded. FGR was defined as a sonographic estimation of fetal weight (EFW) < 10th percentile or abdominal circumference (AC) < 10th percentile. Results: There were 76% significantly lower odds of overall pulse pressure upon admission for those with severe preeclampsia comorbid with FGR (aOR = 0.24, 95% CI = 0.07-0.83). Advanced gestational age on admission was associated with lower odds of severely abnormal labs and severely elevated diastolic blood pressure in preeclampsia also complicated by FGR. Conclusions: Subtypes of preeclampsia with and without FGR may be hemodynamically evaluated by assessing pulse pressure on admission.
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Correlates of Loneliness and Social Isolation among Older Adults during the COVID-19 Outbreak: A Comprehensive Assessment from a National United States SampleThis study examined the correlates of loneliness and social isolation among older adults in the United States (U.S.) during the COVID-19 outbreak. We analyzed data from the 2020 National Health and Aging Trends Study, a nationally representative sample of 3257 U.S. older adults aged 65 years and older. We analyzed and identified the sociodemographic, health, social support, and community correlates of loneliness, higher loneliness during versus before the COVID-19 outbreak, and social isolation using weighted multiple logistic regression models. About 35.2% of U.S. older adults reported loneliness during the COVID-19 outbreak, 21.9% reported higher loneliness compared to before the COVID-19 outbreak, and 32.8% were socially isolated during the outbreak. Correlates for increased odds of loneliness included female gender, higher education, physical activity, depression, anxiety, functional limitations, and virtual communication access (only for higher loneliness during COVID-19 outbreak). Correlates for increased odds of social isolation included higher age, non- Hispanic Black, Hispanic, higher number of household children, and metropolitan residence. Our findings provide insights into evidence-based approaches to address social disconnection among U.S. older adults. The wide range of sociodemographic, health, social support, and community correlates identified in this study warrants multifaceted interventions that traverse individual, community, and societal levels to address the loneliness and social isolation epidemic.
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Association Between Cannabis Use and Subjective Cognitive Decline: Findings from the Behavioral Risk Factor Surveillance System (BRFSS)Background: Cannabis consumption has rapidly increased in the United States due to more states legalizing non-medical and medical use. There is limited research, however, investigating whether cannabis may be associated with cognitive function, particularly across multiple dimensions of cannabis use. Objective: The objective of this study was to examine whether cannabis consumption reason, frequency, and method are associated with subjective cognitive decline (SCD). Methods: Data were obtained from 4,744 U.S. adults aged 45 and older in the 2021 Behavioral Risk Factor Surveillance System (BRFSS). SCD was a self-reported increase in confusion or memory loss in the past year. Odds of SCD by cannabis use reason, frequency, and methods (e.g., smoke, eat, vaporize) were examined using multiple logistic regression after imputing missing data, applying sampling weights, and adjusting for sociodemographic, health, and substance use covariates. Results: Compared to non-users, non-medical cannabis use was significantly associated with 96% decreased odds of SCD (aOR=0.04, 95% CI=0.01-0.44, p<.01). Medical (aOR=0.46, 95% CI=0.06-3.61, p=.46) and dual medical and non-medical use (aOR=0.30, 95% CI=0.03-2.92, p=.30) were also associated with decreased odds of SCD, although not significant. Cannabis consumption frequency and method were not significantly associated with SCD. Conclusion: The reason for cannabis use, but not frequency and method, is associated with SCD. Further research is needed to investigate the mechanisms that may contribute to the observed associations between non-medical cannabis use and decreased odds of SCD.
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Interaction effect of race-ethnicity and dementia on COVID-19 diagnosis among a national US older adult sampleOlder racial and ethnic minorities and older adults with dementia have an elevated COVID-19 risk, warranting research into the intersection between these two high-risk groups. We examined whether race-ethnicity moderates the association between dementia and COVID-19 diagnosis. Data were retrieved for 3189 respondents from a nationally representative prospective cohort sample of US older adults aged 65+ years. We analysed the effects of the interaction between race-ethnicity and dementia on COVID-19 diagnosis, after adjusting for sociodemographic factors, health and COVID-19 mitigation behaviours. The odds of COVID-19 diagnosis were significantly lower for Black older adults with dementia (adjusted odds ratio [aOR] = 0.07, 95% CI = 0.01-0.78, = 0.03). In addition, dementia increased the odds of COVID-19 diagnosis among Hispanic older adults (aOR = 1.59, 95% CI = 0.12-21.29, = 0.72), although this increase was not statistically significant. The interaction between race-ethnicity and dementia should be considered when assessing COVID-19 risk among older adults. Future research is needed to examine pathways through which dementia may interact with race and ethnicity to influence COVID-19 risk.
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Disparities in neighbourhood characteristics and 10-year dementia risk by nativity status.Prior research indicates that neighbourhood disadvantage increases dementia risk. There is, however, inconclusive evidence on the relationship between nativity and cognitive impairment. To our knowledge, our study is the first to analyse how nativity and neighbourhood interact to influence dementia risk.
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Multi-sectoral collaborations to increase recruitment and retention of diverse older adults in biomedical researchBackground Older adults, especially minoritized racial-ethnic groups, are historically underrepresented in biomedical research. This study summarizes the development and assesses the impact of a review board involving a multi-sectoral group of stakeholders with the goal of increasing the diversity of older adults in biomedical research. Methods A 25-member board of community members, caregivers, researchers, and clinicians from Upstate New York reviewed three projects presented by researchers, clinician-scientists, and a pharmaceutical company between January and December 2022. For each biomedical research project, the reviews provided guidance to increase the recruitment and retention of diverse older adults engaged in the study. Review board members and presenters completed surveys to provide feedback on their experience in this collaboration. Results There was consistent positive feedback from all members and presenters. From member surveys, feedback trended positive in meetings throughout the year. Community members and caregivers initially indicated discomfort in expressing their views, however, these concerns subsided over time. Presenters had a very positive experience in the review board’s impact on their recruitment strategy and study design, and therefore very likely to use this service again. Recommendations were made to adjust membership criteria, presentation format, and funding to sustain this effort. Conclusions Lack of diversity for older adults represented in biomedical research contributes to ethical and generalizability ramifications. The positive feedback from all stakeholders in our multi-sectoral board of community members, caregivers, researchers, and clinicians offers a promising structure for developing similar strategies to increase diversity within and beyond biomedical aging research in other communities.
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Racial and Ethnic Disparities in COVID-19 Diagnosis and Adherence to Mitigation Behaviors in a National U.S. Older Adult SampleOlder adults and people of colour are vulnerable to the COVID-19 pandemic, and mitigation behaviours reduce COVID-19 infection. We examined racial and ethnic differences in COVID- 19 diagnosis and adherence to COVID-19 mitigation behaviours among U.S. older adults. Data were retrieved from the National Health and Aging Trends Study, a nationally representative prospective cohort with 3257 U.S. Medicare beneficiaries aged 65+. COVID-19 variables were collected in 2020; all other data in 2019. Odds of COVID-19 diagnosis and adherence to mitigation behaviours (handwashing, masking, social distancing) were analysed using logistic regression. Compared to White older adults, only Hispanic respondents had 2.7 times significantly higher odds of COVID-19 after adjusting for sociodemographics, health, and mitigation behaviours (aOR = 2.71, 95% CI = 1.20-6.12). Black older adults had 7.9 times significantly higher odds of masking (aOR = 7.94, 95% CI = 2.33-27.04) and 2.3 times higher odds of social distancing (aOR = 2.33, 95% CI = 1.28-4.24), after adjusting for sociodemographics and health. Among all racial and ethnic groups, only Hispanic older adults had a significantly elevated COVID-19 diagnosis. Despite higher adherence to COVID-19 mitigation behaviours among racial and ethnic minorities, especially Black older adults, odds of COVID-19 remained elevated. Research is needed to explore potential mechanisms for higher odds of COVID-19 among minority older adults.
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Enhancing response of a protein conformational switch by using two disordered ligand binding domains.Protein conformational switches are often constructed by fusing an input domain, which recognizes a target ligand, to an output domain that establishes a biological response. Prior designs have employed binding-induced folding of the input domain to drive a conformational change in the output domain. Adding a second input domain can in principle harvest additional binding energy for performing useful work. It is not obvious, however, how to fuse two binding domains to a single output domain such that folding of both binding domains combine to effect conformational change in the output domain. Here, we converted the ribonuclease barnase (Bn) to a switchable enzyme by duplicating a C-terminal portion of its sequence and appending it to its N-terminus, thereby establishing a native fold (OFF state) and a circularly permuted fold (ON state) that competed for the shared core in a mutually exclusive fashion. Two copies of FK506 binding protein (FKBP), both made unstable by the V24A mutation and one that had been circularly permuted, were inserted into the engineered barnase at the junctions between the shared and duplicated sequences. Rapamycin-induced folding of FK506 binding protein stretched and unfolded the native fold of barnase the mutually exclusive folding effect, and rapamycin-induced folding of permuted FK506 binding protein stabilized the permuted fold of barnase by the loop-closure entropy principle. These folding events complemented each other to turn on RNase function. The cytotoxic switching mechanism was validated in yeast and human cells, and with purified protein. Thermodynamic modeling and experimental results revealed that the dual action of loop-closure entropy and mutually exclusive folding is analogous to an engine transmission in which loop-closure entropy acts as the low gear, providing efficient switching at low ligand concentrations, and mutually exclusive folding acts as the high gear to allow the switch to reach its maximum response at high ligand concentrations.
