Role of a Disulfide-Bonded Peptide Loop within Human Complement C9 in the Species-Selectivity of Complement Inhibitor CD59

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• 作者：Thomas Hü ; sler ; Dara H. Lockert ; and Peter J. Sims
• 刊名：Biochemistry
• 出版年：1996
• 出版时间：March 12, 1996
• 年：1996
• 卷：35
• 期：10
• 页码：3263 - 3269
• 全文大小：241K
• 年卷期：v.35,no.10(March 12, 1996)
• ISSN：1520-4995

文摘

CD59 antigen is a membrane glycoprotein that inhibits the activityof the C9 component ofthe C5b-9 membrane attack complex (MAC), thereby protecting human cellsfrom lysis by humancomplement. The complement-inhibitory activity of CD59 isspecies-selective, and is most effective towardC9 derived from human or other primate plasma. Thespecies-selective activity of CD59 was recentlyused to map the segment of human C9 that is recognized by this MACinhibitor, using recombinantrabbit/human C9 chimeras that retain lytic function within the MAC[Hüsler, T., Lockert, D. H., Kaufman,K. M., Sodetz, J. M., & Sims, P. J. (1995) J. Biol. Chem.270, 3483-3486]. These experiments suggestedthat the CD59 recognition domain was contained between residues 334 and415 in human C9. By analyzingthe species-selective lytic activity of recombinant C9 with chimericsubstitutions internal to this segment,we now demonstrate that the site in human C9 uniquely recognized byCD59 is centered on those residuescontained between C9 Cys359/Cys384, with an additional contribution byresidues C-terminal to thissegment. Consistent with its role as a CD59 recognition domain,CD59 specifically bound a humanC9-derived peptide corresponding to residues 359-384, and antibody(Fab) raised against this C9-derivedpeptide inhibited the lytic activity of human MAC. Mutant human C9in which Ala was substituted forCys359/384 was found to express normal lytic activity and to be fullyinhibited by CD59. This suggeststhat the intrachain Cys359/Cys384 disulfide bond within C9 is notrequired to maintain the conformationof this segment of C9 for interaction with CD59.