Staphylococcal Protein A Binding to V_H3 Encoded Immunoglobulins

Abstract

Staphylococcal protein A (SPA) is a B-cell superantigen which binds specifically to the variable region of human V_H3 encoded antibodies. We undertook to identify the V_H3 regions involved in the interaction with SPA by producing mutant antibodies in the baculovirus expression system. We had previously shown that a single amino acid change at position 57 in the CDR2 of a human SPA nonbinding V_H3 encoded rheumatoid factor converted it to an SPA binder, implicating CDR2 in SPA binding. When regions of the mutated binder were exchanged with those from a mouse nonbinding antibody, the pattern of SPA binding indicated that residues in FR1, CDR2 and FR3 are involved in the interaction between V_H3 encoded antibodies and SPA. In addition, all three regions are simultaneously required for SPA binding to occur. When any one of the three regions was altered, SPA binding was severely disrupted.

Key Words:

• Baculovirus expression
• SPA binding
• V_H3 encoded antibodies