title: Characterization of a C3-like cDNA in a coral: phylogenetic implications.
abstract: C3, C4, and C5 are thiolester-containing proteins (TEPs) of vertebrate complement. The identification of the molecular origin of the TEP family, and more specifically the ancestor protein of complement components C3, C4, and C5, remains a fundamental question. The prevailing paradigm suggests that duplication and divergence of these proteins occurred after the deuterostome split in phylogeny. It is believed that the ancestor of thiolester-containing complement proteins was alpha-2-macroglobulin (A2M)-like, a noncomplement-related protein. Here we describe a C3-like cDNA from a gorgonian coral, Swiftia exserta. This study provides evidence for the origins of a complement-related C3-like gene in the Precambrian period, predating both protostomes and deuterostomes. Furthermore, one may speculate that complement-like opsonic reactions were evolving at the earliest stages of metazoan evolution. This calls for a reassessment of the present concepts concerning the origins and evolution of TEPs.
authors.affiliation: Department of Biological Sciences, Florida International University, University Park Campus, 11200 SW 8th Street, Miami, FL 33199, USA.
authors.forename: Larry J
authors.initials: LJ
authors.lastname: Dishaw
authors.forename: Sylvia L
authors.initials: SL
authors.lastname: Smith
authors.forename: Charles H
authors.initials: CH
authors.lastname: Bigger
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D037421:Anthozoa / Q000235:genetics* / Q000276:immunology*; D001483:Base Sequence; D003001:Cloning, Molecular; D003176:Complement C3 / Q000235:genetics*; D003165:Complement System Proteins / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D003176:Complement C3; D018076:DNA, Complementary; D003165:Complement System Proteins