Review Article

Thrombin A-Chain: Activation Remnant or Allosteric Effector?

Figure 1

Activation of thrombin by the prothrombinase complex (reviewed in [4]). Prothrombin is colored by domain in this schematic, highlighting the A-chain (pink) and B-chain (yellow). The gamma carboxylated Gla residues are noted by (Y) at the N terminus of prothrombin, the carbohydrate attachment sites in kringle 1 (K1) and the B domain are noted by the shaded star, and the disulfide bridges are shown. Factor Xa initially cleaves Prothrombin (a) at Arg 320 to produce meizothrombin (d), followed by cleavage at Arg 271 to release fragment 1.2 from nascent thrombin (e). Thrombin then undergoes intermolecular autolysis to cleave the Arg 285/Thr 286 bond (f), liberating the A13 peptide (pale pink) to generate α-thrombin. Experimental constructs used in biochemical studies of the thrombin A-chain include prethrombin-1, which lacks fragment 1 (b) and prethrombin-2 (c).
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