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The Ly-6 superfamily of cell surface molecules includes CD59, a potent regulator of the complement system that protects host cells from the cytolytic action of the membrane attack complex (MAC). Although its mechanism of action is not well understood, CD59 is thought to prevent assembly of the MAC by binding to the C8 and/or C9 proteins of the nascent complex. Here a systematic, structure-based mutational approach has been used to determine the region(s) of CD59 required for its protective activity. Analysis of 16 CD59 mutants with single, highly nonconservative substitutions suggests that CD59 has a single active site that includes Trp-40, Arg-53, and Glu-56 of the glycosylated, membrane-distal face of the disk-like extra-cellular domain and, possibly, Asp-24 positioned at the edge of the domain. The putative active site includes residues conserved across species, consistent with the lack of strict homologous restriction previously observed in studies of CD59 function. Competition and mutational analyses of the epitopes of eight CD59-blocking and non-blocking monoclonal antibodies confirmed the location of the active site. Additional experiments showed that the expression and function of CD59 are both glycosylation independent.

Type

Journal article

Journal

J Exp Med

Publication Date

03/02/1997

Volume

185

Pages

507 - 516

Keywords

Amino Acid Sequence, Animals, Antigens, CD59, Binding Sites, CHO Cells, Cricetinae, DNA Mutational Analysis, Epitopes, Glycosylation, Humans, Molecular Sequence Data, Structure-Activity Relationship