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Salmon antithrombin has only three carbohydrate side chains, and shows functional similarities to human Î²âantithrombin
- Andersen, Ãivind, Flengsrud, Ragnar, Norberg, Kari, Salte, Ragnar
- European journal of biochemistry 2000 v.267 no.6 pp. 1651-1657
- Salmo salar, amino acids, binding capacity, binding sites, chickens, coagulation, complementary DNA, galactose, glycosylation, heparin, humans, liver, oligosaccharides, salmon, sequence analysis, sialic acids
- Antithrombin, a major coagulation inhibitor in mammals, has for the first time been cDNA cloned from a fish species. The predicted mature liver antithrombin of Atlantic salmon (Salmo salar) consists of 430 amino acids and shows about 67% sequence identity to mammalian and chicken antithrombins. Due to a single nucleotide replacement, Asn135 of the antithrombin in higher vertebrates is substituted by Asp in the salmon homolog. Hence, in contrast to the vertebrate antithrombins known so far, salmon antithrombin lacks the potential glycosylation site located close to the heparin binding site. The existence of only three Nâlinked side chains is evidenced by the sequential removal of three carbohydrate chains from salmon antithrombin during timedâdigestion with NâglycosidaseâF. The high heparin binding affinity of the salmon inhibitor, Kd of 2.2 and 48ânm at Iâ=â0.15 and 0.3, respectively, is very similar to that of the minor human isoform Î²âantithrombin, which is not glycosylated at Asn135. Furthermore, the invariant thirdâposition Ser137 at this glycosylation site of mammalian and chicken antithrombins is substituted by Thr in the salmon, a replacement that has been shown to induce full glycosylation in human antithrombin. Thus a rapidly reacting pool of antithrombin may have evolved in two different ways: absence of a glycosylation site in lower vertebrates vs. incomplete glycosylation of a part of the circulating antithrombin in higher vertebrates. Salmon antithrombin appears to have three complex oligosaccharide side chains containing sialic acid terminally linked Î±(2â3) to galactose, while trace amounts of GalÎ²(1â4)GlcNAc suggest microheterogeneity due to partial loss of sialic acid.