EXPRESSION AND PURIFICATION OF BIOLOGICALLY-ACTIVE DOMAIN-I OF THE HUMAN POLYMERIC IMMUNOGLOBULIN RECEPTOR

Previous studies using proteolytic fragments and synthetic peptides ha ve indicated that domain I of human polymeric immunoglobulin receptor (PIgR) is necessary for ligand binding. The expression in E. coli, and subsequent IgM-affinity purification of domain I of human PIgR is des cribed. The recombinant domain I protein (rDI) was similar in structur e to native SC domain I in that it bound specifically to MAb 6G11, an antibody which recognizes a critical portion of the Pig binding site i n domain I. The biological activity of rDI was indicated by high affin ity binding to PIgA (Kd = 1.6 X 10(-7) M) and IgM (Kd = 5.1 X 10(-7) M ). Domain I of human SC is therefore sufficient for binding to Pig.