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Background
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Protoxin II is a toxin that was originally isolated from Thrixopelma pruriens (Peruvian green velvet tarantula). Protoxin II inhibits voltage-gated calcium and sodium channels (site 4). This toxin inhibits activation by shifting the voltage-dependence of channel activation to more positive potentials. The toxin potently inhibits all sodium channel subtypes tested (Nav1.2/SCN2A, Nav1.5/SCN5A, Nav1.7/SCN9A, and Nav1.8/SCN10A). It is approximately 15-fold more potent on Nav1.7/SCN9A than on Nav1.5/SCN5A channels and acts on Cav3.1/CACNA1G and interacts more weakly with the related T-Type channel Cav3.2/CACNA1H but potently inhibits the L-type calcium channel Cav1.2/CACNA1C. Protoxin II also binds to phospholipids. ProTx-II, a selective inhibitor of Nav1.7 sodium channels,blocks action potential propagation in nociceptors.
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