Calvert, Peter; Qiu, Shuang (2014)
      The light-driven translocation of arrestin from rod inner segment to outer segment was indicated to involve free diffusion with binding affinityto light-activated phosphorhodopsin, however, it is still debatable how arrestin is excluded from the dark-adapted outer segment. Previousstudies demonstrated that bovine visual arrestin had the property of self-association. The self-association propertyof both wild-type and mutated purified visual arrestin of several species (bovine, mouse and Xenopus laevis) was studiedby performing analytical ultracentrifugation experimentswhich providedthe oligomer formation information and association constants.Theself-association parameters of purified bovine and mousevisual arrestinwere investigated and compared with other studies. Results showed that arrestin of both species could self-associate, forming dimersin a concentration-dependent manner, but tetramerswere not detected at the highest concentrations examined.Xenopus arrestin was shown to self-associateas well, existing in a monomer-dimer equilibrium with the dimer dissociation constantKD,dim=80.8μM, which suggestedthat self-association was also a feature of Xenopus visual arrestin. Interestingly, homologous mutations (F78A/Y84A/F193A)of Xenopusarrestin, which were supposed to beconstitutive monomers, failed to completely disrupt the oligomerizationof Xenopusarrestinwith the dimer dissociation constantKD,dim=200.7μM , indicating that these regions were not conserved in amphibian visual arrestin, includingXenopuslaevis. The percentage of the dimer was higher than that of monomer at physiological concentrations in all species of arrestins tested.