INVOLVEMENT OF THE N-TERMINAL PART OF CYCLOPHILIN-B IN THE INTERACTION WITH SPECIFIC JURKAT T-CELL BINDING-SITES

Cyclophilin B (CyPB) is secreted in biological fluids such as blood or milk and binds to a specific receptor present on the human lymphoblas tic cell line Jurkat and on human peripheral blood lymphocytes. This s tudy was intended to specify the areas of CyPB that are involved in th e interaction with the receptor. A synthetic peptide corresponding to the first 24 N-terminal amino acid residues of CyPB was shown to speci fically recognize the receptor. Moreover, modification of Arg(18) of C yPB by p-hydroxyphenylglyoxal led to a dramatic loss of affinity for t he receptor. However, when this residue was replaced by an alanine res idue using site-directed mutagenesis, no modification of the binding p roperties was found, suggesting that Arg(18) is not directly involved but is sufficiently close to the interaction site to interfere with th e binding when modified. Competitive binding experiments using a chima eric protein made up of the 24 N-terminal amino acid residues of CyPB fused to the cyclophilin A core sequence confirmed the involvement of this region of CyPB in receptor binding.