The thrombin E192Q-BPTI complex reveals gross structural rearrangements: implications for the interaction with antithrombin and thrombomodulin.
Previous crystal structures of thrombin indicate that the 60-insertion loop is a rigid moiety that partially occludes the active site, suggesting that this structural feature plays a decisive role in restricting thrombin's specificity. This restricted specificity is typified by the experimental observation that thrombin is not inhibited by micromolar concentrations of basic pancreatic trypsin inhibitor (BPTI). Surprisingly, a single atom mutation in thrombin (E192Q) results in a 10(-8) M affinity for BPTI. The crystal structure of human thrombin mutant E192Q has been solved in complex with BPTI at 2.3 A resolution. Binding of the Kunitz inhibitor is accompanied by gross structural rearrangements in thrombin. In particular, thrombin's 60-loop is found in a significantly different conformation. Concomitant reorganization of other surface loops that surround the active site, i.e. the 37-loop, the 148-loop and the 99-loop, is observed. Thrombin can therefore undergo major structural reorganization upon strong ligand binding. Implications for the interaction of thrombin with antithrombin and thrombomodulin are discussed.
van de Locht
A
A
Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, Martinsried, Germany.
Bode
W
W
Huber
R
R
Le Bonniec
B F
BF
Stone
S R
SR
Esmon
C T
CT
Stubbs
M T
MT
D000990:Antithrombin III / Q000378:metabolism; D007611:Aprotinin / Q000737:chemistry* / Q000378:metabolism; D003461:Crystallography; D006801:Humans; D006860:Hydrogen Bonding; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D013917:Thrombin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018180:Thrombomodulin / Q000378:metabolism
D018180:Thrombomodulin; D000990:Antithrombin III; D007611:Aprotinin; D013917:Thrombin