Snakebite Therapeutics Based on Endogenous Inhibitors from Vipers

Venomous snakebite is a major human health issue in many countries and has been categorized as a neglected tropical disease by the World Health Organization. Venomous snakes have evolved to produce venom, which is a complex mixture of toxic proteins and peptides, both enzymatic and nonenzymatic in nature. In this current era of high-throughput technologies, venomics projects, which include genome, transcriptome, and proteome analyses of various venomous species, have been conducted to characterize divergent venom phenotypes and the evolution of venom-related genes. Additionally, venomics can also inform about mechanisms of toxin production, storage, and delivery. Venomics can guide antivenom and therapeutic strategies against envenomations and identify new toxin-derived drugs/tools. One potentially promising drug development direction is the use of endogenous inhibitors present in snake venom glands and serum that could be useful for snakebite therapeutics. These inhibitors suppress the activity of venom proteases, enzymatic proteins responsible for the irreversible damage from snakebite. This book chapter will focus on insights from venomous snake adaptations, such as the evolution of venom proteases to generate diverse activities and snake natural resistance to inhibit activity, and how this information can inform and have applications in the treatment of venomous snakebite

Small serum protein-1 changes the susceptibility of an apoptosis-inducing metalloproteinase HV1 to a metalloproteinase inhibitor in habu snake (Trimeresurus flavoviridis)

Viperidae snakes containing various venomous proteins also have several anti-toxic proteins in their sera. However, the physiological function of serum protein has been elucidated incompletely. Small serum protein (SSP)-1 is a major component of the SSPs isolated from the serum of a Japanese viper, the habu snake (Trimeresurus flavoviridis). It exists in the blood as a binary complex with habu serum factor (HSF), a snake venom metalloproteinase inhibitor. Affinity chromatography of the venom on an SSP-1-immobilized column identified HV1, an apoptosis-inducing metalloproteinase, as the target protein of SSP-1. Biacore measurements revealed that SSP-1 was bound to HV1 with a dissociation constant of 8.2 Â 10 À8 M. However, SSP-1 did not inhibit the peptidase activity of HV1. Although HSF alone showed no inhibitory activity or binding affinity to HV1, the SSP-1HSF binary complex bound to HV1 formed a ternary complex that non-competitively inhibited the peptidase activity of HV1 with a inhibition constant of 5.1 AE 1.3 Â 10 À9 M. The SSP-1HSF complex also effectively suppressed the apoptosis of vascular endothelial cells and caspase 3 activation induced by HV1. Thus, SSP-1 is a unique protein that non-covalently attaches to HV1 and changes its susceptibility to HSF. Keywords: apoptosis/proteinase inhibitor/small serum protein/snake serum/snake venom metalloproteinase. Abbreviations: ADAM, a disintegrin and metalloproteinase; ADAMTS, ADAM with thrombospondin type-1 motif; CRISP-3, cysteine-rich secretory protein-3; Dnp, dinitrophenyl; HSF, habu serum factor; HVR, hypervariable region; K i , inhibition constant; Mca, (7-methoxycoumarin-4-yl)-acetyl; MDC, metalloproteinase/disintegrin/ cysteine-rich; MMP, matrix metalloproteinase; PSP94, prostatic secretory protein of 94 amino acids; SSP, small serum protein; SVMP, snake venom metalloproteinase; VEC, vascular endothelial cell