title: The interaction of glycoprotein C of herpes simplex virus types 1 and 2 with the alternative complement pathway.
abstract: Glycoprotein C (gC) of herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2) binds the human complement fragment C3b, but the two proteins differ in their ability to bind C3b on infected cell surfaces. In addition, gC-1, but not gC-2, accelerates the decay of the alternative pathway C3 convertase, thereby affecting later steps of the complement cascade. Previously, we constructed linker insertion and deletion mutants of gC-1 and gC-2 and used transient transfection to express mutant proteins in uninfected cells. In spite of the differences between gC-1 and gC-2, C3b binding was localized to residues within the central portion of both proteins, encompassing the first four cysteines. For gC-1, deletion mutants lacking amino acids 33 to 123 or 367 to 469 or lacking both regions still bound C3b. We recombined these deleted forms of gC-1 into gC-39, an HSV-1 strain lacking the gC gene. The altered forms of gC-1 were incorporated into virions, expressed on the surface of infected cells, and bound C3b. We used these proteins to investigate the structural basis for the inhibitory action of gC-1 on the complement cascade. We found that gC-1 does not inhibit formation of the alternative pathway C3 convertase. This convertase is stabilized by the serum protein properdin. Purified gC-1, but not gC-2, inhibits the binding of properdin to C3b, suggesting that this destabilizes the convertase. The mutant lacking amino acids 367 to 449 was able to inhibit properdin binding to a limited extent when present at high concentrations, although it bound to C3b more weakly than wild-type gC. In contrast, the protein lacking amino acids 33 to 123 was unable to inhibit properdin binding to C3b. Thus, gC-1 contains two structural domains, one for C3b binding, residues 124 to 366, and another, residues 33 to 133, which interferes with properdin binding to C3b.
authors.affiliation: Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104.
authors.forename: S L
authors.initials: SL
authors.lastname: Hung
authors.forename: C
authors.initials: C
authors.lastname: Peng
authors.forename: I
authors.initials: I
authors.lastname: Kostavasili
authors.forename: H M
authors.initials: HM
authors.lastname: Friedman
authors.forename: J D
authors.initials: JD
authors.lastname: Lambris
authors.forename: R J
authors.initials: RJ
authors.lastname: Eisenberg
authors.forename: G H
authors.initials: GH
authors.lastname: Cohen
mesh_terms: D000818:Animals; D015153:Blotting, Western; D003176:Complement C3 / Q000378:metabolism; D003170:Complement Pathway, Alternative; D004797:Enzyme-Linked Immunosorbent Assay; D009154:Mutation; D009500:Neutralization Tests; D011414:Properdin / Q000378:metabolism; D017463:Receptors, Complement 3b / Q000032:analysis; D011994:Recombinant Proteins / Q000096:biosynthesis; D014709:Vero Cells; D014759:Viral Envelope Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*
chemical_list: D003176:Complement C3; D017463:Receptors, Complement 3b; D011994:Recombinant Proteins; D014759:Viral Envelope Proteins; C048232:glycoprotein C, herpes simplex virus type 2; C038535:glycoprotein gC, herpes simplex virus type 1; D011414:Properdin