title: Structural and functional characterization of a novel homodimeric three-finger neurotoxin from the venom of Ophiophagus hannah (king cobra).
abstract: Snake venoms are a mixture of pharmacologically active proteins and polypeptides that have led to the development of molecular probes and therapeutic agents. Here, we describe the structural and functional characterization of a novel neurotoxin, haditoxin, from the venom of Ophiophagus hannah (King cobra). Haditoxin exhibited novel pharmacology with antagonism toward muscle (alphabetagammadelta) and neuronal (alpha(7), alpha(3)beta(2), and alpha(4)beta(2)) nicotinic acetylcholine receptors (nAChRs) with highest affinity for alpha(7)-nAChRs. The high resolution (1.5 A) crystal structure revealed haditoxin to be a homodimer, like kappa-neurotoxins, which target neuronal alpha(3)beta(2)- and alpha(4)beta(2)-nAChRs. Interestingly however, the monomeric subunits of haditoxin were composed of a three-finger protein fold typical of curaremimetic short-chain alpha-neurotoxins. Biochemical studies confirmed that it existed as a non-covalent dimer species in solution. Its structural similarity to short-chain alpha-neurotoxins and kappa-neurotoxins notwithstanding, haditoxin exhibited unique blockade of alpha(7)-nAChRs (IC(50) 180 nm), which is recognized by neither short-chain alpha-neurotoxins nor kappa-neurotoxins. This is the first report of a dimeric short-chain alpha-neurotoxin interacting with neuronal alpha(7)-nAChRs as well as the first homodimeric three-finger toxin to interact with muscle nAChRs.
authors.affiliation: Department of Biological Sciences, National University of Singapore, Singapore.
authors.forename: Amrita
authors.initials: A
authors.lastname: Roy
authors.forename: Xingding
authors.initials: X
authors.lastname: Zhou
authors.forename: Ming Zhi
authors.initials: MZ
authors.lastname: Chong
authors.forename: Dieter
authors.initials: D
authors.lastname: D'hoedt
authors.forename: Chun Shin
authors.initials: CS
authors.lastname: Foo
authors.forename: Nandhakishore
authors.initials: N
authors.lastname: Rajagopalan
authors.forename: Selvanayagam
authors.initials: S
authors.lastname: Nirthanan
authors.forename: Daniel
authors.initials: D
authors.lastname: Bertrand
authors.forename: J
authors.initials: J
authors.lastname: Sivaraman
authors.forename: R Manjunatha
authors.initials: RM
authors.lastname: Kini
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens; D003039:Cobra Neurotoxin Proteins / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D018360:Crystallography, X-Ray; D003964:Diaphragm / Q000187:drug effects / Q000502:physiology; D019281:Dimerization; D004546:Elapid Venoms / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology; D017815:Elapidae; D015723:Gene Library; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D018733:Nicotinic Antagonists / Q000737:chemistry* / Q000494:pharmacology; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D011487:Protein Conformation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000502:physiology*; D013329:Structure-Activity Relationship; D014981:Xenopus; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: C523021:CHRNA1 protein, human; C579167:Chrna7 protein, human; C579166:Chrna7 protein, mouse; C579165:Chrna7 protein, rat; D003039:Cobra Neurotoxin Proteins; D004546:Elapid Venoms; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor