COMPARISON OF NATURALLY-OCCURRING VITAMIN-K-DEPENDENT PROTEINS - CORRELATION OF AMINO-ACID-SEQUENCES AND MEMBRANE-BINDING PROPERTIES SUGGESTS A MEMBRANE CONTACT SITE

Membrane-binding properties of human and bovine forms of vitamin K-dep endent proteins Z, S, and C were characterized. Each of these proteins showed unique properties and interspecies differences that correlated with specific amino acid sequence variations in the amino-terminal 45 residues. Protein Z showed 100-fold slower membrane binding and disso ciation kinetics relative to other vitamin K-dependent proteins that h ave been tested. This property seemed to correlate with an extra gamma -carboxyglutamic acid (Gla) residue at position 11 of protein Z. The i nterspecies difference for protein Z consisted of a higher packing den sity for the bovine protein on the membrane and a 9-fold slower dissoc iation rate. Higher affinity correlated with Asp at position 34 of bov ine protein Z, where the human protein contains Asn. While both protei n S species showed high affinity for the membrane, it was significantl y greater for the human protein versus bovine protein S. Again, higher affinity correlated with an Asp (vs Asn) at position 34. Protein C wa s characterized by binding affinities that were 100-1000-fold lower th an the other proteins. Low affinity appeared to be related to loss of Gla-32 (homologous to Gla-33 of protein Z). Interspecies differences o f protein C appeared to be related to proline at position 10 (homologo us to position 11 of protein Z) of bovine protein C, which produced at least 10-fold lower affinity than the human protein. Comparable subst itutions at positions homologous to 11, 33, and 34 of protein Z may al so underlie membrane binding behaviors of other vitamin K-dependent pr oteins. The three-dimensional structure of strontium-prothrombin fragm ent 1 [Seshadri et al. (1993) Biochemistry 33, 1087] shows that these positions are clustered on the protein surface near strontium-8, anoth er possible candidate for membrane contact. A membrane contact mechani sm consisting of an isolated protein-lipid ion pair is proposed. Compa rison of naturally occurring vitamin K-dependent proteins has provided possible bases for divergent membrane binding and suggested future ap proaches to determine biological function.