6rc7 | pdb_00006rc7
NMR structure of cytotoxin 3 from Naja kaouthia in solution, major form
Structural highlights
Function[3SA3_NAJKA] Monomer: shows cytolytic activity.[1] Heterodimer: has no cytolytic activity, but retains most of the alpha-cobratoxin capacity to compete with alpha-bungarotoxin for binding to Torpedo and alpha-7/CHRNA7 nicotinic acetylcholine receptors (nAChRs) as well as to Lymnea stagnalis acetylcholine-binding protein.[2] Publication Abstract from PubMedCobra cytotoxins (CTs), the three-fingered proteins, feature high amino acid sequence homology in the beta-strands and variations in the loop regions. We selected a pair of cytotoxins from Naja kaouthia crude venom to clarify the sequence-structure relationships. Using chromatography and mass spectroscopy, we separated and identified the mixture of cytotoxins 2 and 3, differentiated by the only Val 41/Ala 41 substitution. Here, using natural abundance (13)C, (15)N NMR-spectroscopy we performed chemical shift assignments of the signals of the both toxins in aqueous solution in the major and minor forms. Combining NOE and chemical shift data, the toxins' spatial structure was determined. Finally, we proved that the tip of the "finger"-2, or the loop-2 of cytotoxins adopts the shape of an omega-loop with a tightly-bound water molecule in its cavity. Comparison with other NMR and X-ray structures of cytotoxins possessing different amino acid sequences reveals spatial similarity in this family of proteins, including the loop-2 region, previously considered to be flexible. The omega-loop of cobra cytotoxins tolerates multiple amino acid substitutions.,Dubinnyi MA, Dubovskii PV, Starkov VG, Utkin YN Biochem Biophys Res Commun. 2021 Jun 18;558:141-146. doi:, 10.1016/j.bbrc.2021.04.069. Epub 2021 Apr 26. PMID:33915327[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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