Sequence characterization of a sheep cDNA for antithrombin III

Purification and characterization of alpha(1)-proteinase inhibitor and antithrombin III: major serpins of rainbow trout (Oncorhynchuss mykiss) and carp (Cyprinus carpio) blood plasma

The main serine proteinase inhibitors of rainbow trout (Oncorhynchuss mykiss) and common carp (Cyprinus carpio) blood plasma were isolated and purified. The investigated inhibitors, alpha(1)-proteinase inhibitor (alpha(1)-PI) and antithrombin III (AT III), act by forming stable complexes with target proteinases. The association rate constants k (on) for the interaction of fish plasma inhibitors with several serine proteinases have been determined: k (on) for both carp and rainbow trout alpha(1)-PI were >10(7) M(-1) s(-1) for human neutrophil elastase, and in the case of bovine trypsin and chymotrypsin k (on) values were 2.0-5.2 x 10(6) M(-1) s(-1). Association rate constants k (on) for the interaction of carp and rainbow trout AT III with bovine trypsin and thrombin were about 1.3 x 10(4)-7.9 x 10(5) M(-1) s(-1) without and >10(7) M(-1) s(-1) in presence of heparin; so antithrombins require the presence of heparin to become effective proteinase inhibitors. The high degree of homology of the estimated amino acid sequences of fish inhibitors reactive site loops confirms their similarity with other proteinase inhibitors from the serpin family.

Presence and localization of antithrombin and its regulation after acute lipopolysaccharide exposure in amphioxus, with implications for the origin of vertebrate liver

Antithrombin (AT), which is mainly synthesized in the liver, is an acute-phase plasma protein in mammalian species. Here, we demonstrated that sheep anti-human AT antibody cross-reacted with the humoral fluids in amphioxus Branchiostoma belcheri tsingtauense as well as human serum. The concentration of AT in the humoral fluids in amphioxus decreased slightly at first and then increased after the acute challenge with lipopolysaccharide, while the level of total proteins remained unchanged. These suggest the presence of the same acute-phase response pattern in amphioxus, as observed in some mammalian species. Immunohistochemically, AT was localized in the hepatic diverticulum. It is clear that the hepatic diverticulum in amphioxus is homologous to the vertebrate liver with respect to AT synthesis. This lends support to the hypothesis originally suggested by Müller that the vertebrate liver evolved from the hepatic diverticulum of an amphioxus-like ancestor during early chordate evolution.

Hamster antithrombin III: purification, characterization and acute phase response

Antithrombin III was purified to homogeneity from hamster plasma by affinity chromatography on heparin-agrose, ion-exchange chromatography on Mono Q and size-exclusion chromatography on TSK G3000SWG column with 50% yield. The molecular mass of hamster antithrombin III was estimated at 62.5 kDa and the absorption coefficient (A280 nm 1%, 1 cm) at 6.48 (in 0.1 M sodium phosphate pH 7.0). Several isoforms of the inhibitor were detected with the pI in range of 4.95-5.25. The protein contains all residues characteristic for complex-type carbohydrate chains. The N-terminal amino acid sequence shows 84% of identity to mouse and 76% to human analogue. The hamster antithrombin III gives low immunological cross-reactivity with antibodies to human antithrombin III. Initiation of the acute phase response only slightly affected the plasma concentration of inhibitor (+/- 10% within 72-h period). The kinetic data suggest high efficiency in bovine and human thrombin inhibition. In summary, the study shows only similarities between hamster and other mammal antithrombins.

Molecular genetics of antithrombin deficiency

Antithrombin is the major proteinase inhibitor of thrombin and other blood coagulation proteinases. Antithrombin has two functional domains, a heparin binding site and a reactive centre (that complexes and inactivates the proteinase). Its deficiency results in an increased risk of venous thromboembolism. Appreciable progress has been made in recent years in understanding the structure and function of this protein, the genetic cause of inherited deficiency and its clinical consequence. The structure of antithrombin is now considered in terms of the models derived from X-ray crystallography, which have provided explanations for the function of its heparin interaction site and of its reactive loop. The structural organization of the antithrombin gene has been defined and numerous mutations have been identified that are responsible for antithrombin deficiency: these may reduce the level of the protein (Type I deficiency), alter the function of the protein (Type II deficiency, altering heparin binding or reactive sites), or even have multiple or 'pleiotropic effects' (Type II deficiency, altering both functional domains and the level of protein).

Fetal and neonatal development of antithrombin III plasma activity and liver messenger RNA levels in sheep

In healthy term human newborns a unique hemostatic balance exists with reduced plasma concentrations of several coagulant and anticoagulant proteins, including antithrombin III (AT III). In preterm newborns even lower AT III concentrations are observed, with an associated thromboembolic risk. As part of our study program on the gene regulation of AT III, we investigated whether the increase in plasma AT III activity during fetal and neonatal development is particularly controlled at the transcriptional level. Plasma AT III activity and liver AT III mRNA content between the 8th wk of gestation and the 4th wk after birth were determined in sheep. AT III activity gradually increased from 34% of the mean adult level at 8-10 wk of gestation to 86% (2.5-fold) at term (21 wk), and remained in the adult range after birth. The mean body weight, and thus plasma volume, increased 57-fold. Therefore, the total plasma AT III activity increased 140-fold. The total liver AT III mRNA content increased only 14-fold between these fetal stages, mainly due to increased liver weight. Therefore, the total plasma AT III activity increased 10-fold more than the liver AT III mRNA content. In the neonatal period between d 1-3 and 28, the total plasma AT III activity increased only 2-fold more than the liver AT III mRNA content. We conclude that the increase in plasma AT III activity during the fetal period, and similarly the neonatal period, is not regulated at the transcriptional level. Furthermore, a unique fetal isoform of AT III was detected in sheep. This isoform had a 2500-D higher molecular mass compared with the other fetal, neonatal, and adult AT III isoform, and disappeared from the circulation between d 2 and 7 after birth. These AT III isoforms differ in their carbohydrate moiety.

Molecular genetics of human antithrombin deficiency

Human antithrombin is the major plasma inhibitor of thrombin both in the presence and absence of heparin. Its physiological importance is emphasised by the recurrent thromboses that individuals with a deficient or functionally abnormal protein are prone to develop. Such deficiencies are estimated to affect as many as 1:630 of the general population and between 3% and 5% of patients with thrombotic disease. The gene for antithrombin (AT3) has been cloned and shown to map to the long arm of chromosome 1 at 1q23-25. The gene consists of seven exons and six introns and spans 13,477bp of DNA. Advances in molecular genetic techniques have facilitated identification of the underlying DNA mutation(s) in > 80 families with antithrombin deficiency. Such work has proved invaluable in structure-function studies and in helping to provide informed genetic counselling to "at-risk" individuals based upon the natural history of similar variants.

Partial glycosylation of antithrombin III asparagine-135 is caused by the serine in the third position of its N-glycosylation consensus sequence and is responsible for production of the beta-antithrombin III isoform with enhanced heparin affinity

Two antithrombin III (ATIII) isoforms occur naturally in human plasma. The alpha-ATIII isoform has four N-linked oligosaccharides attached to asparagines 96, 135, 155, and 192. The beta-ATIII isoform lacks carbohydrate on asparagine-135 (N135), which is near the heparin binding site, and binds heparin with higher affinity than does alpha-ATIII. Two isoforms are also produced when the normal human ATIII cDNA sequence is expressed in baculovirus-infected insect cells, and the recombinant beta' isoform similarly binds heparin with higher affinity than the recombinant alpha' isoform. Consensus sequences (CSs) of the ATIII N-glycosylation sites are N-X-S for 135 and N-X-T for 96, 155, and 192. On the basis of database and in vitro glycosylation studies suggesting that N-X-S CSs are utilized less efficiently than N-X-T CSs, we hypothesized that the beta-ATIII isoform might result from inefficient core glycosylation of the N135 N-X-S CS due to the presence of a serine, rather than a threonine, in the third position. ATIIIs with N-X-S, N-X-T, and N-X-A consensus sequences were expressed in baculovirus-infected insect cells. In contrast to the N-X-S sequence, which expressed a mixture of alpha' and beta' molecules, the N-X-T variant produced alpha' exclusively, while the N-X-A variant produced beta' exclusively. Thus, serine in the third position of the N135 CS is responsible for its "partial" glycosylation and leads to production of beta-ATIII.(ABSTRACT TRUNCATED AT 250 WORDS)

The molecular genetics of familial venous thrombosis

This study of naturally occurring mutations predisposing to venous thrombosis has led to a number of important advances in our understanding of protein structure and function relationships and the molecular basis of gene mutation. It has also potentiated the accurate and reliable presymptomatic and antenatal detection of predisposing gene lesions. Perhaps the major challenge facing us is the probabilistic nature of thromboembolism; only a certain proportion of patients with recognized gene defects predisposing to thrombosis will actually suffer from thrombotic episodes. Environmental insults of various kinds, and perhaps epistatic effects resulting from the influence of other loci, are likely to be contributory factors and will help to determine whether a thrombotic event occurs in individuals already compromised by a defect in a gene whose malfunction is known to predispose to thrombosis. Since molecular genetic techniques allow us to dissect the allelioheterogeneity of the different deficiency states by characterizing the wide spectrum of gene mutations giving rise to thrombosis, it may eventually prove possible to relate specific gene lesions to the probability of thromboembolism as well as to the severity and frequency of thrombotic episodes. The multifactorial nature of thrombosis demands a multidisciplinary approach to the analysis of its causation, early detection, treatment and prevention. The application of the new and powerful techniques of molecular genetics promises to make a substantial contribution to all aspects of thrombosis research.