Conformational restriction of the Tyr53 side-chain in the decapeptide HEL[52-61]:: effects on binding to MHC-II I-Ak molecule and TCR recognition

A series of conformationally restricted analogs of the hen egg lysozyme (HEL) decapeptide 52-61 in which the conformationally flexible Tyr(53) residue was replaced by several more constrained tyrosine and phenylalanine analogs was prepared. Among these tyrosine and phenylalanine analogs were 1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid (Htc), 1,2,3,4-tetrahydroisoquinoline-3-carboxy acid (Tic), 4-amino-1,2.4,5-tetrahydro-8-hydroxy-2-benzazepine-3-one (Hba), 4-amino-1,2.4,5-tetrahydro-2-benzazepine-3-one (Aba), 2-amino-6-hydroxytetralin-2-carboxylic acid (Hat) and 2-amino-5-hydroxyindan-2-carboxylic acid (Hai) in which the rotations around C-alpha-C-beta and C-beta-C-gamma were restricted because of cyclization of the side-chain to the backbone. Synthesis of Pht-Hba-Gly-OH using a modification of the Flynn and de Laszlo procedure is described. Analogs of B-methyltyrosine (beta -MeTyr) in which the side-chains were biased to particular side-chain torsional angles because of substitution at the P-hydrogens were also prepared. These analogs of HEL[52-61] peptide were tested for their ability to bind to the major histocompatibility complex class II I-A(k) molecule and to be recognized in this context by two T-cell hybridomas, specific for the parent peptide HEL[52-61]. The data showed that the conformation and also the configuration of the Tyr(53) residue influenced both the binding of the peptide to I-Ak and the recognition of the peptide/I-A(k) complex by a T-cell receptor.