Zg. Chen et al., CRYSTAL-STRUCTURE OF HUMAN ALPHA-THROMBIN COMPLEXED WITH HIRUGEN AND P-AMIDINOPHENYLPYRUVATE AT 1.6 ANGSTROM RESOLUTION, Archives of biochemistry and biophysics, 322(1), 1995, pp. 198-203
Crystals of human alpha-thrombin complexed with hirugen and the alpha-
keto acid thrombin inhibitor APPA (p-amidinophenylpyruvate) that diffr
act to 1.6 Angstrom resolution were obtained by soaking an alpha-throm
bin-hirugen crystal in a solution of APPA. The crystal structure was d
etermined using the difference Fourier method and refined to an R fact
or of 18.7% at 1.6 Angstrom resolution. This structure is the highest
resolution structure of the thrombin molecule that is currently availa
ble. With the exception of the region near Arg77A-Asn78, the structure
s of the thrombin and hirugen molecules in the ternary complex are sim
ilar to those reported for the thrombin-hirugen binary complex. As pre
viously determined for the APPA-trypsin complex, the carbonyl carbon a
tom of APPA forms a covalent bond with O gamma of Ser195 of thrombin t
o yield a ''transition-state'' analog of the tetrahedral intermediate.
Comparison of the specificity pocket of the APPA complexes of thrombi
n and trypsin reveals differences in hydrogen bonding and shows for th
e first time that the S1 site of thrombin is larger than that of tryps
in and as a result thrombin may be able to accommodate a bulkier P1 gr
oup than trypsin. (C) 1995 Academic Press, Inc.