NEW LIGANDS BINDING TO THE HUMAN-LEUKOCYTE ANTIGEN CLASS-II MOLECULE DRB1(ASTERISK)0101 BASED ON THE ACTIVITY PATTERN OF AN UNDECAPEPTIDE LIBRARY

Major histocompatibility complex (MHC) class II molecules present pept ide antigens to CD4(+)-T cells. These heterogeneous peptides are deriv ed from internalized exogenous proteins or from endogenous membrane pr oteins that are processed by the antigen-presenting cell. Peptides are bound to the MHC class II molecules in an extended conformation and e xtend out of the binding groove. The aim of this study was to estimate the influence of every amino acid in all the possible undecapeptide a mides (2.048X10(14) individuals) on the binding to human MHC-DRB10101 molecules (HLA-DR1) and to identify new peptide ligands. 220 undecape ptide sublibraries, O/X(10), each composed of ten degenerate positions and one defined position, were screened for binding to isolated HLA-D R1. Competition of the sublibraries with a fluorescence-labeled peptid e ligand allowed definition of the amino acids favourable or unfavoura ble for DR1-binding at every sequence position. From the activity patt ern of the undecapeptide library, 54 individual peptides were deduced (27 potential hits and 27 potential falls) and prepared by chemical sy nthesis. As anticipated, 27 positive and 27 negative results were obta ined from the competition experiments. The 27 peptides that bind obey the rules for the HLA-DR1-binding motif. The synthetic peptide library approach proved to be valuable for the design of synthetic MHC class II ligands and thus can be considered as a basis for drug design in im munotherapy.