Insertional mutagenesis and immunochemical analysis of visual arrestin interaction with rhodopsin

Visual arrestin inactivates the phototransduction cascade by specifically binding to light-activated phosphorylated rhodopsin. This study describes the combined use of insertional mutagenesis and immunochemical approaches to probe the structural determinants of arrestin function. Recombinant arrestins with insertions of a 10-amino acid c-Myc tag (EQKLISEEDL) were expressed in yeast and characterized. When the tag was placed on the C terminus after amino acid 399, between amino acids 99 and 100 or between residues 162 and 163, binding to rhodopsin was found to be very similar to that of wild-type arrestin. Two stable mutants with Myc insertions in the 68-78 loop were also generated. Binding to rhodopsin was markedly decreased for one (72myc73) and completely abolished for the other (77myc78). Limited proteolysis assays using trypsin in the absence or presence of heparin were performed on all mutants and confirmed their overall conformational integrity. Rhodopsin binding to either 162myc163 or 72myc73 arrestins in solution was completely inhibited in the presence of less than a 2-fold molar excess of anti-Myc antibody relative to arrestin. In contrast, the antibody did not block the interaction of the 399myc or 99myc100 arrestins with rhodopsin. These results indicate that an interactive surface for rhodopsin is located on or near the concave region of the N-domain of arrestin.