Induced fit of an epitope peptide to a monoclonal antibody probed with a novel parallel surface plasmon resonance assay.
Class II major histocompatibility complex proteins bind peptides for presentation to T-cells as part of the immune response process. Monoclonal antibody MEM-265 recognizes the peptide-free conformation of the major histocompatibility complex class II protein HLA-DR1 through specific binding to an epitope contained between residues 50-67 of the beta-chain. In previous work using alanine scanning (1), we identified residues Leu-53, Asp-57, Tyr-60, Trp-61, Ser-63, and Leu-67 as essential for specific recognition by MEM-265. The spacing of these residues approximates a 3.5-residue repeat, suggesting that MEM-265 may recognize the epitope in an alpha-helical conformation. In the folded, peptide-loaded DR1 structure, the beta-chain residues 50-67 contain a kinked alpha-helical segment spanning Glu-52-Ser-63 (2). However, the conformation of this segment in the peptide-free form is unknown. We have used a new surface plasmon resonance approach in a SpotMatrix format to compare the kinetic rates and affinities for 18 alanine scanning mutants comprising epitope residues 50-67. In addition to the six essential residues described previously, we found two additional residues, Glu-52 and Gln-64, that contribute by enhancing MEM-265 binding. By contrast, mutation of either Gly-54 or Pro-56 to an alanine actually improved binding to MEM-265. In essentially all cases peptide substitutions that either improve or reduce MEM-265 recognition could be traced to differences in the dissociation rate (k off). The kinetic details of the present study support the presence of a structural component in the antigenic epitope recognized by MEM-265 in the peptide-free form of major histocompatibility complex II DR1 beta-chain.
Baggio
Rick
R
HTS Biosystems, East Hartford, Connecticut 06108, USA.
Carven
Gregory J
GJ
Chiulli
Anthony
A
Palmer
Michelle
M
Stern
Lawrence J
LJ
Arenas
Jaime E
JE
D000409:Alanine / Q000737:chemistry; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry*; D015374:Biosensing Techniques; D019921:Biotinylation; D018604:Epitope Mapping / Q000379:methods; D000939:Epitopes / Q000737:chemistry*; D005998:Glycine / Q000737:chemistry; D006825:Hybridomas / Q000276:immunology; D007700:Kinetics; D008024:Ligands; D051379:Mice; D008956:Models, Chemical; D008958:Models, Molecular; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D011392:Proline / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D020349:Surface Plasmon Resonance / Q000295:instrumentation* / Q000379:methods*; D013997:Time Factors
D000911:Antibodies, Monoclonal; D000939:Epitopes; D008024:Ligands; D010455:Peptides; D011392:Proline; D000409:Alanine; D005998:Glycine