Two distinct regions of cyclophilin B are involved in the recognition of afunctional receptor and of glycosaminoglycans on T lymphocytes

Cyclophilin B is a cyclosporin A-binding protein exhibiting peptidyl-prolyl cis/trans isomerase activity. We have previously shown that it interacts w ith two types of binding sites on T lymphocytes. The type I sites correspon d to specific functional receptors and the type II sites to sulfated glycos aminoglycans. The interactions of cyclophilin B with type I and type II sit es are reduced in the presence of cyclosporin A and of a synthetic peptide mimicking the N-terminal part of cyclophilin B, respectively, suggesting th at the protein possesses two distinct binding regions. In this study, we in tended to characterize the areas of cyclophilin B involved in the interacti ons with binding sites present on Jurkat cells. The use of cyclophilin B mu tants modified in the N-terminal region demonstrated that the (3)Lys-Lys-Ly s(5) and (14)Tyr-Phe-Asp(16) clusters are probably solely required for the interactions with the type II sites. We further engineered mutants of the c onserved central core of cyclophilin B, which bears the catalytic and the c yclosporin A binding sites as an approach to localize the binding regions f or the type I sites. The enzymatic activity of cyclophilin B was dramatical ly reduced after substitution of the Arg(62) and Phe(67) residues, whereas the cyclosporin A binding activity was destroyed by mutation of the Trp(128 ) residue and strongly decreased after modification of the Phe(67) residue. Only the substitution of the Trp(128) residue reduced the binding of the r esulting cyclophilin B mutant to type I binding sites. The catalytic site o f cyclophilin B therefore did not seem to be essential for cellular binding and the cyclosporin A binding site appeared to be partially involved in th e binding to type I sites.