Molecular modeling of the prekallikrein structure provides insights into high-molecular-weight kininogen binding and zymogen activation.

Abstract

Prekallikrein (PK) plays a central role in the contact system that activates blood coagulation and is involved in the regulation of blood pressure. To provide three-dimensional structural data for PK and rationalize the molecular basis of substrate recognition and zymogen activation. The PK homology model was constructed using the coagulation factor (F) XI crystal structure as a template with the program SWISS-MODEL. The domain organization of the PK apple domains and serine protease is conserved compared to FXI. Surface charge calculations on the PK model revealed that ligand binding to high-molecular-weight kininogen (HK) is predicted to have two key determinants: a pocket within the apple 2 domain and a basic channel formed at the interface of apple domains 1 and 4. A hereditary mutation resulting in PK deficiency (Gly104Arg) and the Lys140 alpha-kallikrein cleavage site both disrupt HK binding and are shown to map to opposite sides of the apple 2 domain pocket. The model also describes the differences in the apple 4 domain that prevents dimer formation in PK vs. FXI. A C-terminal extension in the PK serine protease domain is described as a potential substrate for prolylcarboxypeptidase. The interaction between PK and HK is mediated by two discrete surfaces formed by the PK A1, A2 and A4 domains with charge likely to be a critical component of the binding. A novel mode of PK activation is postulated to involve prolylcarboxypeptidase cleaving at the C-terminus rather than the activation loop.