Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) open reading frame 4 protein (kaposica) is a functional homolog of complement control proteins

J Virol. 2003 Mar;77(6):3878-81. doi: 10.1128/jvi.77.6.3878-3881.2003.


The genome analysis of Kaposi's sarcoma-associated herpesvirus (KSHV) has revealed the presence of an open reading frame (ORF 4) with sequence homology to complement control proteins. To assign a function to this protein, we have now expressed this ORF using the Pichia expression system and shown that the purified protein inhibited human complement-mediated lysis of erythrocytes, blocked cell surface deposition of C3b (the proteolytically activated form of C3), and served as a cofactor for factor I-mediated inactivation of complement proteins C3b and C4b (the subunits of C3 convertases). Thus, our data indicate that this KSHV inhibitor of complement activation (kaposica) provides a mechanism by which KSHV can subvert complement attack by the host.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Cloning, Molecular
  • Complement Activation*
  • Complement Inactivator Proteins / pharmacology
  • Gene Expression Regulation
  • Herpesvirus 8, Human / genetics
  • Herpesvirus 8, Human / metabolism*
  • Humans
  • Open Reading Frames*
  • Pichia / genetics
  • Pichia / metabolism
  • Viral Proteins / chemistry
  • Viral Proteins / genetics
  • Viral Proteins / physiology*


  • Complement Inactivator Proteins
  • Viral Proteins