Two diverged complement factor B/C2-like cDNA sequences from a teleost, the common carp (Cyprinus carpio).
Mammalian complement components factor B and C2 act as proteolytic subunits of the C3 convertases in the alternative and the classical activation pathways, respectively, and are believed to have diverged from a common ancestor by gene duplication. However, it is unclear when the B/C2 duplication occurred. Here, we describe two diverged B/C2-like cDNA clones (B/C2-A and B/C2-B) isolated from a bony fish, the common carp (Cyprinus carpio). B/C2-A shares the same domain structure as the factor B and C2 complement components of vertebrates reported so far and shows a close similarity to zebrafish B and medaka fish B/C2. These teleost sequences show almost the same degree of similarity to C2 and B of higher vertebrates. In contrast, B/C2-B has a novel structural feature in that it contains four short consensus repeat modules and does not have a close relative upon phylogenetic analysis. Northern blotting revealed the presence of two transcripts with different sizes for both the B/C2-A and B/C2-B in the hepatopancreas of the carp. Southern blotting suggested the presence of multiple genes for B/C2-A and a single gene for B/C2-B. Although structural features of B/C2-B are slightly more C2-like than B-like, B/C2-B has a crucial amino acid substitution in the serine protease domain, which makes it unlikely that B/C2-B functions as a C3 convertase. A possible phylogenetic relationship between the two carp sequences and mammalian C2 and B is discussed.
Nakao
M
M
Laboratory of Marine Biochemistry, Faculty of Agriculture, Kyushu University, Fukuoka, Japan.
Fushitani
Y
Y
Fujiki
K
K
Nonaka
M
M
Yano
T
T
D000595:Amino Acid Sequence; D000818:Animals; D002347:Carps / Q000235:genetics*; D003175:Complement C2 / Q000235:genetics*; D011415:Complement Factor B / Q000235:genetics*; D016384:Consensus Sequence; D018076:DNA, Complementary / Q000235:genetics*; D019143:Evolution, Molecular; D020440:Gene Duplication; D005796:Genes; D006801:Humans; D008322:Mammals / Q000235:genetics; D015336:Molecular Probe Techniques; D008969:Molecular Sequence Data; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
D003175:Complement C2; D018076:DNA, Complementary; D011415:Complement Factor B