THE RELATIVE IMPORTANCE OF INDIVIDUAL DR BINDING MOTIF POSITIONS AS DEFINED BY PEPTIDE ANCHOR ANALYSIS OF INFLUENZA HEMAGGLUTININ PEPTIDE-306-318 AND HUMAN MYELIN BASIC-PROTEIN PEPTIDE-152-165 BINDING TO SEVERAL DR MOLECULES - DEFINITION OF A COMMON EXTENDED DR BINDING MOTIF

Definition of peptide binding motifs for DR molecules has proven diffi cult as the peptides that bind to a DR molecule have shown extensive v ariability at putative motif positions. Recent studies suggest that sp ecific peptide anchor residues (motif positions) and specific DR resid ues can differ in importance for peptide binding to a DR molecule. To assess further the relevance of individual peptide anchor residues, th e binding of serial alanine-substituted analogs of influenza virus hem agglutinin (HA) 306-318 and human myelin basic protein (MBP) 152-165 t o a panel of transfected wild-type DR molecules was examined. This ana lysis included DR molecules from a wide range of allelic families and, unlike most earlier studies, multiple members of single DR allelic fa milies. The data show that different peptide residues serve as critica l anchors for binding to different DR molecules. For example, MBP bind ing to DR(alpha,beta 10303) required peptide residues F154 (i), R159 (i + 5) and R162 (i + 8). In contrast, MBP binding to DR(alpha,beta 1 0102) required peptide residues 1153 (i) and L156 (i + 3). More import antly, the combination of critical anchor residues in HA and MBP diffe red for binding to a single DR molecule [e.g. V309 (i) for HA and 1153 (i) and L156 (i + 3) for MBP binding to DR(alpha,B10102)]. Although the location of the binding pocket in each DR molecule compared to the DR (alpha,beta 10101) crystal is expected to be similar and suggests a common extended DR binding motif, the present results suggest that the relative importance of individual peptide anchor residues and of t he corresponding DR binding pockets will differ for each DR/peptide co mplex.