Dendrotoxin
Dendrotoxins are a class of presynaptic
Dendrotoxins have been shown to block particular subtypes of voltage-gated potassium (K+) channels in neuronal tissue.[
Dendrotoxin structure
Dendrotoxins are ~7kDa proteins consisting of a single peptide chain of approximately 57-60
The dendrotoxins are structurally homologous to the
Dendrotoxins are
Biological activity
Pharmacology
A single dendrotoxin molecule associates reversibly with a potassium channel in order to exert its inhibitory effect. It is proposed that this interaction is mediated by
Biologically important residues
Many studies have attempted to identify which amino acid residues are important for binding activity of dendrotoxins to their potassium channel targets. Harvey et al.[5] used residue-specific modifications to identify positively charged residues that were crucial to the blocking activity of dendrotoxin-I. They reported that acetylation of Lys5 near the N-terminal region and Lys29 in the beta-turn region led to substantial decreases in DTX-I binding affinity. Similar results have been shown with dendrotoxin-K using site-directed mutagenesis to substitute positively charged lysine and arginine residues to neutral alanines. These results, along with many others, have implicated that the positively charged lysines in the N-terminal half, particularly Lys5 in the 310-helix, play a very important role in the dendrotoxin binding to their potassium channel targets. The lysine residues in the β-turn region has provided more confounding results, appearing to be biologically critical in some dendrotoxin homologues and not necessary for others. Furthermore, mutation of the entire lysine triplet (K28-K29-K30) to Ala-Ala-Gly in alpha-DTX resulted in very little change in biological activity.
There is a general agreement that the conserved lysine residue near the N-terminus (Lys5 in alpha-DTX) is crucial for the biological activity of all dendrotoxins, while additional residues, such as those in the beta-turn region, might play a role in dendrotoxin specificity by mediating the interactions of individual toxins to their individual target sites. This not only helps explain the stringent specificity of some dendrotoxins for different subtypes of voltage-gated K+ channels, but also accounts for differences in the potency of dendrotoxins for common K+ channels. For example, Wang et al.[6] showed that the interaction of dendrotoxin-K with KV1.1 is mediated by its lysine residues in both the N-terminus and the β-turn region, while alpha-dendrotoxin appears to interact with its target solely through the N-terminus. This less expansive interactive domain may help explain why alpha-dendrotoxin is less discriminative while dendrotoxin-K is strictly selective for KV1.1.
Uses in research
Potassium channels of vertebrate neurons display a high degree of diversity that allows neurons to precisely tune their electrical signaling properties by expression of different combinations of potassium channel subunits. Furthermore, because they regulate ionic flux across biological membranes, they are important in many aspects of cellular regulation and signal transduction of different cell types. Therefore, voltage-gated potassium channels are targets for a wide range of potent biological toxins from such organisms as snakes, scorpions, sea anemones, and cone snails. Thus, venom purification has led to the isolation of peptide toxins such as the dendrotoxins, which have become useful pharmacological tools for the study of potassium channels. Because of their potency and selectivity for different subtypes of potassium channels, dendrotoxins have become useful as molecular probes for the structural and functional study of these proteins. This may help improve our understanding of the roles played by individual channel types, as well as assist in the pharmacological classification of these diverse channel types.[7] Furthermore, the availability of radiolabelled dendrotoxins provides a tool for the screening of other sources in a search for new potassium channel toxins, such as the kalicludine class of potassium channel toxins in sea anemones. Lastly, the structural information provided by dendrotoxins may provide clues to the synthesis of therapeutic compounds that may target particular classes of potassium channels. Dendrotoxin I has also been used to help purify and characterize the K+ channel protein to which it binds via different binding assay and chromatography techniques.[8]
References
- ^ Gasparini S, Danse J-M, Licoq A, Pinkasfeld S, Zinn-Justin S, Young LC, C.L. de Medeiros C, Rowan EG, Harvey AL, and Me’nez A (1998). Delineation of the Functional Site of alpha-dendrotoxin: The functional topographies of dendrotoxins are different but share a conserved core with those of other KV1 potassium channel-blocking toxins. Journal of Biological Chemistry 273:25393-25403
- ^ Katoh E, Nishio H, Inui T, Nishiuchi Y, Kimura T, Sakakibara S, Yamazaki T (2000). Structural Basis for the Biological Activity of Dendrotoxin-I, a Potent Potassium Channel Blocker. Biopolymers 54:44-57
- ^ Swaminathan P, Hariharan M, Murali R, Singh CU (1996). Molecular Structure, Conformational Analysis, and Structure-Activity Studies of Dendrotoxin and Its Homologues Using Molecular Mechanics and Molecular Dynamics Techniques. Journal of Medicinal Chemistry. 39:2141-2155
- ^ Imredy JP, and MacKinnon R (2000). Energetic and Structural Interactions between delta-Dendrotoxin and a Voltage-gated Potassium Channel. Journal of Molecular Biology 296:1283-1294
- ^ Harvey AL, Rowan EG, Vatanpour H, Engstrom A, Westerlund B, Karlsson E (1997). Changes to biological activity following acetylation of dendrotoxin I from Dendroaspis polylepis (black mamba). ' 35:1263-1273
- ^ Wang FC, Bell N, Reid P, Smith LA, McIntosh P, Robertson B, and Dolly JO (1999). Identification of residues in dendrotoxin K responsible for its discrimination between neuronal K+ channels containing KV1.1 and 1.2 alpha subunits. European Journal of Biochemistry 263:222-229
- ^ Yoshida S and Matsumoto S (2005). Effects of alpha-dendrotoxin on K+ currents and action potentials in tetrodotoxin-resistant adult rat trigeminal ganglion neurons. Journal of Pharmacology and Experimental Therapeutics 314:437-445
- PMID 2455300.
External links
- dendrotoxin at the U.S. National Library of Medicine Medical Subject Headings (MeSH)