3r0l
From Proteopedia
Crystal structure of crotoxin
Structural highlights
Function[PA2B_CRODU] Heterodimer CA-CB: Crotoxin is a potent presynaptic neurotoxin that possesses phospholipase A2 (PLA2) activity and exerts a lethal action by blocking neuromuscular transmission. It consists of a non-covalent association of a basic and weakly toxic PLA2 subunit (CBa2, CBb, CBc, or CBd), with a small acidic, non-enzymatic and non-toxic subunit (CA1, CA2, CA3 or CA4). The complex acts by binding to a specific 48-kDa protein (R48) receptor located on presynaptic membranes, forming a transient ternary complex CA-CB-R48, followed by dissociation of the CA-CB complex and release of the CA subunit. At equilibrium, only the CB subunits remain associated with the specific crotoxin receptor. In addition to neurotoxicity, crotoxin has been found to exert myotoxicity, nephrotoxicity, and cardiovascular toxicity (PubMed:20109480). Moreover, anti-inflammatory, immunomodulatory, anti-tumor and analgesic effects of crotoxin have also been reported (PubMed:20109480).[1] [2] [3] [REFERENCE:12] Monomer CBc: The basic subunit of crotoxin is a snake venom phospholipase A2 (PLA2) that exhibits weak neurotoxicity (10-fold less than the heterodimer) and very strong anticoagulant effects by binding to factor Xa (F10) and inhibiting the prothrombinase activity (IC(50) is 0.7 nM) (PubMed:18062812). In addition, it shows the same effects described for the heterodimer and binds the nucleotide-binding domain (NBD1) of CFTR chloride channels and increases the channel current. PLA2 catalyzes the calcium-dependent hydrolysis of the 2-acyl groups in 3-sn-phosphoglycerides.[4] [5] [6] [REFERENCE:12] Publication Abstract from PubMedThe crystal structure of crotoxin, a potent presynaptic neurotoxin from Crotalus durissusterrificus, was solved at 1.35 A resolution. It shows the architecture of the three disulfide-linked polypeptide chains (alpha, beta, and gamma) of the acidic subunit CA noncovalently complexed with the basic phospholipase A(2) (PLA(2)) subunit CB. The unique structural scaffold of the association of the CA and CB subunits indicates that posttranslational cleavage of the pro-CA precursor is a prerequisite for the assembly of the CA-CB complex. These studies provide novel structural insights to explain the role of the CA subunit in the mechanism of action of crotoxin. The crystal structure of the highly toxic and stable CA(2)CBb complex crystallized here allows us to identify key amino acid residues responsible for significant differences in the pharmacological activities of the two classes of crotoxin complexes. In particular, we show that critical residues Trp31 and Trp70 of the CBb subunit establish intermolecular polar contacts with Asp99 and Asp89, respectively, of the beta-chain of CA(2) and contribute to the stability and toxicity of the CA(2)CBb complex. These interactions also lead to decreased PLA(2) activity by partially blocking substrate access to the catalytic dyad and by masking several interfacial binding surface residues important for PLA(2) interaction with phospholipids. Identification of the binding interface between the CA subunits and the CB subunits of crotoxin is important for the structure-based design of antineurotoxic inhibitors. Since crotoxin displays numerous physiological functions, including antitumoral properties, knowledge of its three-dimensional structure will be useful for the understanding of these diverse effects. Crystal structure of crotoxin reveals key residues involved in the stability and toxicity of this potent heterodimeric beta-neurotoxin.,Faure G, Xu H, Saul FA J Mol Biol. 2011 Sep 16;412(2):176-91. Epub 2011 Jul 23. PMID:21787789[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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