Multiple forms of complement C3 in trout that differ in binding to complement activators

Proc Natl Acad Sci U S A. 1996 Aug 6;93(16):8546-51. doi: 10.1073/pnas.93.16.8546.


In all other species analyzed to date, the functionally active form of complement component C3 exists as the product of a single gene. We have now identified and characterized three functional C3 proteins (C3-1, C3-3, and C3-4) in trout that are the products of at least two distinct C3 genes. All three proteins are composed of an alpha-and a beta-chain and contain a thioester bond in the alpha-chain. However, they differ in their electrophoretic mobility, glycosylation, reactivity with monospecific C3 antibodies, and relative ability to bind to various surfaces (zymosan, Escherichia coli, erythrocytes). A comparison of the partial amino acid sequences of the three proteins showed that the amino acid sequence identity/similarity of C3-3 to C3-4 is 87/91%, while that of C3-3 and C3-4 to C3-1 is 51.5/65.5% and 60/73% respectively. Thus, trout possess multiple forms of functional C3 that represent the products of several distinct genes and differ in their ability to bind covalently to various complement activators.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Complement Activation*
  • Complement C3 / chemistry
  • Complement C3 / genetics
  • Complement C3 / physiology*
  • Consensus Sequence
  • Cross Reactions
  • DNA Primers / chemistry
  • Humans
  • Molecular Sequence Data
  • Oncorhynchus mykiss / genetics
  • Oncorhynchus mykiss / immunology*
  • Protein Binding
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Structure-Activity Relationship


  • Complement C3
  • DNA Primers

Associated data

  • GENBANK/U61753