title: A novel serpin with antithrombin-like activity in Branchiostoma japonicum: implications for the presence of a primitive coagulation system.
abstract: Serine protease inhibitors, or serpins, are a group of widely distributed proteins with similar structures that use conformational change to inhibit proteases. Antithrombin (AT) is a member of the serine protease inhibitor superfamily and a major coagulation inhibitor in all vertebrates, but its evolutionary origin remains elusive. In this study we isolated for the first time a cDNA encoding an antithrombin homolog, BjATl, from the protochordate Branchiostoma japonicum. The deduced protein BjATl consisted of 338 amino acids sharing 36.7% to 41.1% identity to known vertebrate ATs. BjATl contains a potential N-linked glycosylation site, two potential heparin binding sites and the reactive center loop with the absolutely conserved sequence Gly-Arg-Ser; all of these are features characteristic of ATs. All three phylogenetic trees constructed using Neighbor-Joining, Maximum-Likelihood and Bayesian-Inference methods also placed BjATl together with ATs. Moreover, BjATl expressed in yeast cells was able to inhibit bovine thrombin activity by forming a SDS-stable BjATl-thrombin complex. It also displays a concentration-dependent inhibition of thrombin that is accelerated by heparin. Furthermore, BjATl was predominantly expressed in the hepatic caecum and hind-gut, agreeing with the expression pattern of AT in mammalian species. All these data clearly demonstrate that BjATl is an ortholog of vertebrate ATs, suggesting that a primitive coagulation system emerged in the protochordate.
authors.affiliation: Department of Marine Biology, Ocean University of China, Qingdao, China.
authors.forename: Yeqing
authors.initials: Y
authors.lastname: Chao
authors.forename: Chunxin
authors.initials: C
authors.lastname: Fan
authors.forename: Yujun
authors.initials: Y
authors.lastname: Liang
authors.forename: Bei
authors.initials: B
authors.lastname: Gao
authors.forename: Shicui
authors.initials: S
authors.lastname: Zhang
mesh_terms: D000818:Animals; D058833:Antithrombin Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D001499:Bayes Theorem; D005075:Biological Evolution; D001777:Blood Coagulation / Q000235:genetics* / Q000502:physiology; D002417:Cattle; D002816:Chordata, Nonvertebrate / Q000737:chemistry* / Q000502:physiology; D018076:DNA, Complementary / Q000235:genetics; D016013:Likelihood Functions; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D015843:Serpins / Q000235:genetics* / Q000378:metabolism; D013045:Species Specificity; D013917:Thrombin / Q000378:metabolism
chemical_list: D058833:Antithrombin Proteins; D018076:DNA, Complementary; D015843:Serpins; D013917:Thrombin