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Expression and purification of biologically active domain I of the human polymeric immunoglobulin receptor
M A Bakos1, S G Widen, R M Goldblum
1Department of Pediatrics, University of Texas Medical Branch, Galveston 77555-0366.
Previous studies using proteolytic fragments and synthetic peptides have 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 described. The recombinant domain I protein (rDI) was similar in structure 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 in domain I. The biological activity of rDI was indicated by high affinity 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.
Previous studies using proteolytic fragments and synthetic peptides have 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 described. The recombinant domain I protein (rDI) was similar in structure 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 in domain I. The biological activity of rDI was indicated by high affinity 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.