Evidence for the α-helicity of class II MHC molecular binding sites for the superantigen, staphylococcal enterotoxin A

Abstract

Circular dichroism (CD) spectra of class II MHC peptides revealed the α-helical conformation of superantigen-binding peptides I-A β b (60–90), I-A β b (65–85), and I-A α b (51–80), but not the nonbinding peptide I-A β b (80–100). These CD spectra provide biophysical evidence for the α-helicity of class II MHC molecular binding sites for the superantigen, staphylococcal enterotoxin A (SEA). Alanine-substituted analogs of the SEA binding-site peptide, I-A β b (65–85), were used to implicate β-chain residues 72 and 80 in class II MHC-SEA binding. The data support SEA binding away from the class II antigen binding cleft along the faces of the α-helices.