Mapping the Intermedilysin-Human CD59 Receptor Interface Reveals a Deep Correspondence with the Binding Site on CD59 for Complement Binding Proteins C8α and C9

Stephanie E Wickham,Eileen M Hotze,Allison J Farrand,Galina Polekhina,Tracy L Nero,Stephen Tomlinson,Michael W Parker,Rodney K Tweten

doi:10.1074/jbc.m111.237446

Abstract

CD59 is a glycosylphosphatidylinositol-anchored protein that inhibits the assembly of the terminal complement membrane attack complex (MAC) pore, whereas Streptococcus intermedius intermedilysin (ILY), a pore forming cholesterol-dependent cytolysin (CDC), specifically binds to human CD59 (hCD59) to initiate the formation of its pore. The identification of the residues of ILY and hCD59 that form their binding interface revealed a remarkably deep correspondence between the hCD59 binding site for ILY and that for the MAC proteins C8α and C9. ILY disengages from hCD59 during the prepore to pore transition, suggesting that loss of this interaction is necessary to accommodate specific structural changes associated with this transition. Consistent with this scenario, mutants of hCD59 or ILY that increased the affinity of this interaction decreased the cytolytic activity by slowing the transition of the prepore to pore but not the assembly of the prepore oligomer. A signature motif was also identified in the hCD59 binding CDCs that revealed a new hCD59-binding member of the CDC family. Although the binding site on hCD59 for ILY, C8α, and C9 exhibits significant homology, no similarity exists in their binding sites for hCD59. Hence, ILY and the MAC proteins interact with common amino acids of hCD59 but lack detectable conservation in their binding sites for hCD59.

Highlights

Fellow. 2 An Australian Research Council Federation Fellow and a National Health and brane attack complex/perforin proteins complement C8␣, a C9-like protein from Photorhabdus luminescens, and mouse perforin [1,2,3,4] suggested that they are structurally and mechanistically related the CDCs [5,6,7] and may be ancient ancestors [8]
Two members of the CDC family, intermedilysin (ILY) secreted by Streptococcus intermedius and vaginolysin (VLY) secreted by Gardnerella vaginalis, bind to the human form of CD59, a glycosylphosphatidylinositol (GPI)-anchored terminal inhibitor of the mammalian complement membrane attack complex (MAC) [9], rather than cholesterol [10, 11]. These CDCs bind to hCD59 to initiate the assembly of their oligomeric pore complex on the membrane of human cells [10], whereas the main function of CD59 is to block the assembly of the MAC pore on host cells, thereby protecting them from the lytic effects of activated complement MAC
The surface area of hCD59 covered by these substitutions is shown in Fig. 1, except for those residues shown below to be misfolded after alanine substitution

Summary

Introduction

Fellow. 2 An Australian Research Council Federation Fellow and a National Health and brane attack complex/perforin proteins complement C8␣, a C9-like protein from Photorhabdus luminescens, and mouse perforin [1,2,3,4] suggested that they are structurally and mechanistically related the CDCs [5,6,7] and may be ancient ancestors [8]. Two members of the CDC family, intermedilysin (ILY) secreted by Streptococcus intermedius and vaginolysin (VLY) secreted by Gardnerella vaginalis, bind to the human form of CD59 (hCD59), a glycosylphosphatidylinositol (GPI)-anchored terminal inhibitor of the mammalian complement membrane attack complex (MAC) [9], rather than cholesterol [10, 11]. These CDCs bind to hCD59 to initiate the assembly of their oligomeric pore complex on the membrane of human cells [10], whereas the main function of CD59 is to block the assembly of the MAC pore on host cells, thereby protecting them from the lytic effects of activated complement MAC. We further show that the residues of ILY that contribute to its binding site for hCD59 appear to be a signature motif for hCD59 binding CDCs

Methods

Results

Conclusion