X-Ray Crystallography of Blood Coagulation Proteins and Transferrins
His laboratory takes a crystallographic approach to address five fundamental questions: How is protein function defined by structure? What determines and mediates protein-protein and protein-membrane interactions? How does information get passed from one protein to another? How do protein cofactors modulate enzymes? How does structure prescribe the binding affinity of a metal? Two model systems are being studied to explore these basic questions. Both involve synergistic interactions: first, proteins which either amplify, propagate or terminate the blood coagulation response; and second, transferrin, the major plasma protein responsible for iron transport, interacting with its specific receptor.
Factor V is a large (330 kDa), single chain, coagulation cofactor which is proteolytically activated by other coagulation factors. As a start to providing a real structural understanding of the cofactors we, in collaboration with Dr. Kenneth G. Mann (Biochemistry), have solved the structure of bovine factor Vai (Figure 1).
Transferrin (80 kDa) is a glycoprotein with two homologous lobes. Each lobe consists of two domains that form a deep cleft which bind a single Fe (III) ion in conjunction with the concomitant binding of a carbonate ion in a pH dependent manner (Figure 2). In collaboration with Dr. Anne B. Mason (Biochemistry) we have begun crystallizing mutants of the N-lobe of human serum transferrin in order to understand the iron uptake and release properties of this protein.