RECEPTOR-BINDING DOMAIN OF HUMAN ALPHA(2)-MACROGLOBULIN - EXPRESSION, FOLDING AND BIOCHEMICAL-CHARACTERIZATION OF A HIGH-AFFINITY RECOMBINANT DERIVATIVE

A recombinant version of the receptor binding domain (RBDv) of human alpha(2)-macroglobulin (alpha(2)M) has been expressed in E. coli and refolded using a novel iterative procedure. RBDv C(Val(1299)-Ala(1451)) is extended by 15 residues at the N-terminal side of the Lys(1313)-Glu papain cleavage site in human alpha(2)M. RBDv contains the intra-chain bridge Cys(1329)-Cys(1444) and is soluble and monomeric. Competition experiments with I-125-labelled methylamine-treated alpha(2)M reveal that RBDv binds to the placental receptor for transformed alpha(2)M with a K-d of 8 nM, i.e. the binding affinity of RBDv is of the same order of magnitude as the intrinsic affinity for binding of one domain in transformed alpha(2)M to one receptor molecule.