Abstract
Venomous snakes have endogenous proteins that neutralize the toxicity of their venom components. We previously identified five small serum proteins (SSP-1-SSP-5) from a highly venomous snake belonging to the family Viperidae as inhibitors of various toxins from snake venom. The endogenous inhibitors belong to the prostate secretory protein of 94 amino acids (PSP94) family. SSP-2 interacts with triflin, which is a member of the cysteine-rich secretory protein (CRISP) family that blocks smooth muscle contraction. However, the structural basis for the interaction and the biological roles of these inhibitors are largely unknown. Here, we determined the crystal structure of the SSP-2-triflin complex at 2.3 Å resolution. A concave region centrally located in the N-terminal domain of triflin is fully occupied by the terminal β-strands of SSP-2. SSP-2 does not bind tightly to the C-terminal cysteine-rich domain of triflin; this domain is thought to be responsible for its channel-blocker function. Instead, the cysteine-rich domain is tilted 7.7° upon binding to SSP-2, and the inhibitor appears to sterically hinder triflin binding to calcium channels. These results help explain how an endogenous inhibitor prevents the venomous protein from maintaining homeostasis in the host. Furthermore, this interaction also sheds light on the binding interface between the human homologues PSP94 and CRISP-3, which are up-regulated in prostate and ovarian cancers.
Highlights
Venomous snakes have endogenous proteins that neutralize the toxicity of their venom components
Venomous snakes possess three groups of endogenous antivenom components, which are found in snake serum as follows: (a) an antihemorrhagic factor that inhibits snake venom metalloproteases [6, 7], (b) the phospholipase A2 inhibitors [8], and (c) the small serum proteins (SSPs; SSP-1–SSP-5) previously discovered by us, which bind directly to toxic components (9 –11)
We determined the crystal structure of the SSP-2–triflin complex at 2.3 Å resolution using native proteins derived from snake serum and venom; these proteins possess many disulfide bonds and are difficult to produce in sufficient amounts from typical recombinant expression systems (Fig. 1 and Table S1)
Summary
Venomous snakes have endogenous proteins that neutralize the toxicity of their venom components. The cysteine-rich domain is tilted 7.7° upon binding to SSP-2, and the inhibitor appears to sterically hinder triflin binding to calcium channels These results help explain how an endogenous inhibitor prevents the venomous protein from maintaining homeostasis in the host. This interaction sheds light on the binding interface between the human homologues PSP94 and CRISP-3, which are up-regulated in prostate and ovarian cancers. SSPs and triflin have human homologues: The prostate secretory protein of 94 amino acids (PSP94) and CRISP-3, respectively [2, 10] These endogenous antivenom groups remain unclear because of the lack of information on the three-dimensional structures of toxin and inhibitor complexes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
