Most proteins in nature are chemically modified after they are made to control how, when, and where they function. The 3 core features of proteins are posttranslationally modified: amino acid side chains can be modified, peptide bonds can be cleaved or isomerized, and disulfide bonds can be cleaved. Cleavage of peptide bonds is a major mechanism of protein control in the circulation, as exemplified by activation of the blood coagulation and complement zymogens. Cleavage of disulfide bonds is emerging as another important mechanism of protein control in the circulation. Recent advances in our understanding of control of soluble blood proteins and blood cell receptors by functional disulfide bonds is discussed as is how these bonds are being identified and studied.

We demonstrate mechanochemical regulation of platelet adhesion to von Willebrand factor in thrombosis and hemostasis.

Snake venom metalloproteinases (SVMPs) are widely distributed in snake venoms and play important roles in hemostatic disorders and local tissue damage that follows snakebite. The impact of SVMPs on hemostasis has been extensively studied showing diverse effects both on soluble factors and cellular components. The action of SVMPs involves catalytic and anti-adhesive properties, as well as direct cellular activation and/or the release of endogenous bioactive components. The purpose of this review is to overview the action of SVMPs on the inhibition of platelet functions; angiogenesis, particularly inducing apoptosis of endothelial cells; and regarding the pro-inflammatory reaction that follows snakebite. We discuss the structural features of the molecules that may be involved in such activities. The versatility and availability of SVMPs make them important tools for cell biology research into the mechanisms of action of endogenous metalloproteinases, for insights into cellular-matrix interactions and for clinical investigations into the treatment of snakebites.

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SVMPs are multi-domain proteolytic enzymes in which disintegrin-like and cysteine-rich domains bind to cell receptors, plasma or ECM proteins. We have recently reported that jararhagin, a P-III class SVMP, binds to collagen with high affinity through an epitope located within the Da-disintegrin sub-domain. In this study, we evaluated the binding of jararhagin to alpha(2)beta(1) integrin (collagen receptor) using monoclonal antibodies and recombinant jararhagin fragments. In solid phase assays, binding of jararhagin to alpha(2)beta(1) integrin was detectable from concentrations of 20 nM. Using recombinant fragments of jararhagin, only fragment JC76 (residues 344-421), showed a significant binding to recombinant alpha(2)beta(1) integrin. The anti-jararhagin monoclonal antibody MAJar 3 efficiently neutralised binding of jararhagin to collagen, but not to recombinant alpha(2)beta(1) integrin nor to cell-surface-exposed alpha(2)beta(1) integrin (alpha(2)-K562 transfected cells and platelets). The same antibody neutralised collagen-induced platelet aggregation. Our data suggest that jararhagin binding to collagen and alpha(2)beta(1) integrin occurs by two independent motifs, which are located on disintegrin-like and cysteine-rich domains, respectively. Moreover, toxin binding to collagen appears to be sufficient to inhibit collagen-induced platelet aggregation.

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Disulfide bonds link pairs of cysteine amino acids and their formation is assumed to be complete in the mature, functional protein. Here, we test this assumption by quantifying the redox state of disulfide bonds in the blood clotting protein fibrinogen. The disulfide status of fibrinogen from healthy human donor plasma and cultured human hepatocytes are measured using differential cysteine alkylation and mass spectrometry. This analysis identifies 13 disulfide bonds that are 10–50% reduced, indicating that fibrinogen is produced in multiple disulfide-bonded or covalent states. We further show that disulfides form upon fibrin polymerization and are required for a robust fibrin matrix that withstands the mechanical forces of flowing blood and resists premature fibrinolysis. The covalent states of fibrinogen are changed by fluid shear forces ex vivo and in vivo, indicating that the different states are dynamic. These findings demonstrate that fibrinogen exists and functions as multiple covalent forms.