Maurotoxin. Maurotoxin (MTX) is a 34 amino acid long toxin, isolated from the venom of the scorpion Scorpio Maurus palmatus, and is classified as alpha-KTx6.2 scorpion toxin family, having four disulfide bridges.
MTX activity was extensively assayed on a large array of K\+\ channels, including K\ca\ (K\ca\1.1, K\ca\2.1, K\ca\2.2, K\ca\3.1), Kv1 (K\v\1.1, K\v\1.2 and K\v\1.3) and Shaker B K\+\ currents.
MTX inhibits the binding of \125\I-Apamin and \125\I-Kaliotoxin to rat brain synaptosomal membranes with an IC50 of 5 nM and 30 pM, respectively.
Furthermore, MTX blocks KCNA1 (K\V\1.1), KCNA2 (K\V\1.2) and KCNA3 (K\V\1.3) expressed in Xenopus oocyes with an IC50 of 45 nM, 0.8 nM, and 180 nM, respectively.
Maurotoxin blocks Shaker-B K\+\ current with an IC50 of 2 nM. In contrast to previous reports, MTX was recently shown to have no effect on K\ca\1.1, K\ca\2.1 and K\ca\2.2 small conductance K\ca\ channels up to 300 nM in physiologically relevant ionic strength buffers, but rather produces a high and specific block towards K\ca\3.1 (IK\ca\1, SK4) and KCNA2 (K\V\1.2) with IC50 of 1 nM and 0.1 nM, respectively.
Furthermore, MTX was shown to block Gardos channel in human red blood cells and to inhibit the K\ca\ in activated human T-lymphocytes without affecting the voltage-gated K\+\ current encoded by KCNA3. Moreover, MTX inhibition was shown to be pH-dependent.
In conclusion, Maurotoxin seems to be a very potent blocker of both K\Ca\3.1 and K\v\1.2 channels.
Ion Channel Modulators; K\+\ Channel Blockers
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