“Progress Toward the Structure of a Crustacean Clotting Protein”
Justin Kollman – Department of Biochemistry and Biophysics, UC San Francisco
Higher animals have evolved several distinct systems for stopping the loss of internal fluids upon injury. These clotting systems range from the proteolytic activation of fibrinogen to form polymers in vertebrates, to cell-clumping type responses in echinoderms. In crustaceans, hemolymph clotting is the result of transglutaminase-mediated polymerization of a large, dimeric clottable protein (CP). CP carries a bound carotenoid pigment, and is homologous to vitellogenins, a class of lipid transport proteins. This homology suggests an evolutionary history of clotting in crustaceans that is distinct from other phyla. CP from the California spiny lobster has been purified and crystallized, but phasing the crystal data has proven difficult. We are in the process of determining a low-resolution cryo-EM structure which may be useful in phasing the crystal data by molecular replacement. A preliminary EM map shows several general features which can be compared with the crystal structure of a vitellogenin, especially the size of the lipid-binding cavity.