H-1-NMR CONFORMATIONAL-ANALYSIS OF A HIGH-AFFINITY ANTIGENIC 11-RESIDUE PEPTIDE FROM THE TRYPTOPHAN SYNTHASE BETA-2 SUBUNIT

Two synthetic peptides from the beta-2 subunit of tryptophan synthase have been studied by H-1-NMR spectroscopy at 300 MHz. One peptide, His-Gly-Arg-Val-Gly-Ile-Tyr-Phe-Gly-Met-Lys (peptide 11; Ile, isoleucine) is antigenic and binds with a high affinity to a monoclonal antibody that recognizes the native beta-2 subunit. The second peptide, His-Gly-Arg-Val-Gly-Ile-Tyr-Phe (peptide 8) reacts very weakly with the antibody. The H-1-NMR spectra of the two peptides have been assigned from two-dimensional techniques in H2O, (H2O)-H-2 and (H-2(6)) dimethyl sulfoxide [(H-2(6))Me2SO]. The structure has been evaluated through analysis of nuclear Overhauser effects, coupling constants, amide-proton exchange rates and their temperature coefficients, and chemical shifts. In aqueous solvent, the C-terminal part of peptide 11 presents some structure centered around residues Phe-Gly-Met. The relationship between the structure found in peptide 11 and its antigenic nature is discussed.