FUNCTIONAL-CHANGES IN SCAVENGER RECEPTOR-BINDING CONFORMATION ARE INDUCED BY CHARGE MUTANTS SPANNING THE ENTIRE COLLAGEN DOMAIN

Macrophage scavenger receptors are trimeric integral membrane proteins that bind a diverse array of negatively charged ligands, They have be en shown to play a role in the pathogenesis of atherosclerosis and in host responses to microbial infections. Earlier mutational studies dem onstrated that the distal segment of the collagen domain of the recept or was critically important for high affinity ligand binding activity. In this study, mutations spanning the entire collagen domain were gen erated and binding was assayed in transfected cells, as well as in ass ays employing a secreted, receptor fusion protein, Many of the distal, positively charged C-terminal residues in the type II collagen domain of the receptor, previously reported to be essential for binding at 3 7 degrees C, were found not to be critical for binding at 4 degrees C, Conversely, more proximally charged residues of the collagen receptor that have not been previously mutated were shown to have substantial effects on binding that were also temperature-dependent. These data su ggest that scavenger receptor ligand recognition depends on more compl ex conformational interactions, involving charged residues throughout the entire collagen domain, than was previously recognized.