TOPOGRAPHIC STUDY OF ARRESTIN USING DIFFERENTIAL CHEMICAL MODIFICATIONS AND HYDROGEN-DEUTERIUM EXCHANGE

Arrestin is involved in the quenching of phototransduction by binding to photoactivated and phosphorylated rhodopsin (P-Rho*). To study its conformational changes and regions interacting with P-Rho*, arrestin was subjected to (1) differential acetylation at lysine residues in the presence and absence of P-Rho*, and (2) amide hydrogen/deuterium exchange. Labeled protein was proteolysed and analyzed by mass spectrometry. Three Lys residues, 28, 176, and 211, were protected from acetylation in native arrestin, although they were not located in regions exhibiting slow amide hydrogen exchange rates. The presence of P-Rho* protected lysine 201 from acetylation and partially protected 14 other lysyl residues, including (2, 5), (163, 166, 167), (232, 235, 236, 238), (267, 276), (298, 300), and 367, where parentheses indicate lysine residues found within the same peptide. In contrast, in the C-terminal region of arrestin, lysyl residues (386, 392, 395) were more exposed upon binding to P-Rho*, These data allowed us to identify functional regions in the arrestin molecule.