CRYSTALLOGRAPHIC DETERMINATION OF THE STRUCTURES OF HUMAN ALPHA-THROMBIN COMPLEXED WITH BMS-186282 AND BMS-189090

The crystallographic structures of the ternary complexes of human alph a-thrombin with hirugen (a sulfated hirudin fragment) and the small-mo lecule active site thrombin inhibitors BMS-186282 and BMS-189090 have been determined at 2.6 and 2.8 Angstrom. In both cases, the inhibitors , which adopt very similar bound conformations, bind in an antiparalle l beta-strand arrangement relative to the thrombin main chain in a man ner like that reported for PPACK, D-Phe-Pro-Arg-CH2Cl. They do, howeve r, exhibit differences in the binding of the alkyl guanidine moiety in the specificity pocket. Numerous hydrophilic and hydrophobic interact ions serve to stabilize the inhibitors in the binding pocket. Although PPACK forms covalent bonds to both serine and the histidine of the ca talytic triad of thrombin, neither BMS-186282 nor BMS-189090 bind cova lently and only BMS-186282 forms a hydrogen bond to the serine of the catalytic triad. Both inhibitors bind with high affinity (K-i = 74 nM and 3.6 nM, respectively) and are highly selective for thrombin over t rypsin and other serine proteases.