Separation between the alpha and beta forms of human antithrombin by hydroxyapatite high-performance liquid chromatography

Comparison of biological activities of human antithrombins with high-mannose or complex-type nonfucosylated N-linked oligosaccharides

The structure of the N-linked oligosaccharides attached to antithrombin (AT) has been shown to affect its anticoagulant activity and pharmacokinetics. Human AT has biantennary complex-type oligosaccharides with the unique feature of lacking a core fucose, which affects its biological activities by changing its heparin-binding affinity. In human plasma, AT circulates as a mixture of the α-form bearing four oligosaccharides and the β-form lacking an oligosaccharide at Asn135. However, it remains unclear how the immature high-mannose-type oligosaccharides produced by mammalian cells affect biological activities of AT. Here, we succeeded in directly comparing the activities between the high-mannose and complex types. Interestingly, although there were no substantial differences in thrombin inhibitory activity, the high-mannose type showed higher heparin-binding affinity. The anticoagulant activities were increased by heparin and correlated with the heparin-binding affinity, resulting in the strongest anticoagulant activity being displayed in the β-form with the high-mannose type. In pharmacokinetic profiling, the high-mannose type showed a much shorter plasma half-life than the complex type. The β-form was found to have a prolonged plasma half-life compared with the α-form for the high-mannose type; conversely, the α-form showed a longer half-life than the β-form for the complex-type. The present study highlights that AT physiological activities are strictly controlled not only by a core fucose at the reducing end but also by the high-mannose-type structures at the nonreducing end. The β-form with the immature high-mannose type appears to function as a more potent anticoagulant than the AT typically found in human plasma, once it emerges in the blood.

Expression and purification of an influenza hemagglutinin--one step closer to a recombinant protein-based influenza vaccine

Numerous human infections with avian influenza viruses in Asia in recent years have raised the concern that the next influenza pandemic is imminent. The most effective way to combat influenza is through the vaccination of the public. However, a minimum of 3–6 months is needed to develop an influenza vaccine using the traditional egg-based vaccine approach. The influenza hemagglutinin protein (HA), the active ingredient in the current vaccine, can be expressed in insect cells using the baculovirus expression vector system and purified rapidly. An influenza vaccine based on such a recombinant antigen allows a more timely response to a potential influenza pandemic. Here, we report an innovative monitoring assay for recombinant HA (rHA) expression and a rapid purification process. Various biochemical analyses indicate that the purified rHA is properly folded and biologically active.

Separation of latent, prelatent, and native forms of human antithrombin by heparin affinity high-performance liquid chromatography

Latent antithrombin (LAT) is a partially denatured form of human antithrombin (AT). LAT does not inhibit clotting of the blood, but has previously been shown to inhibit angiogenesis and carcinogenesis. Another probably partially denatured form is the so-called prelatent AT (P-LAT), described by Larsson et al. [J. Biol. Chem. 276 (2001) 11996]. In the present work, an analytical heparin affinity chromatography method is described that separates an AT form, which is formed during the pasteurization process and which we believe to be identical to the previously described P-LAT, from native AT and LAT. Non-pasteurized AT was shown to contain no P-LAT, while four, heat-treated commercial AT products all contained P-LAT (1-6%, mean=4%). P-LAT has a slightly lower affinity to heparin than does native AT, but exhibits a much stronger heparin affinity when compared to LAT. P-LAT and native AT were shown to have very similar thrombin inhibiting activity, while LAT lacks such activity.