Fig. 1.

Native and recombinant MmTX1 and MmTX2 are equally potent. (A) Picture of the Costa Rican coral snake M. mipartitus (provided by Alejandro Solórzano). (B) Primary amino acid sequences of MmTX1 and MmTX2. Note the different residue at position 33 (gray background). (C) Competition experiments for the binding of ¹²⁵I-rMmTX2 to synaptosomes with WT MmTX1, rMmTX1, rMmTX2, and the rMmTX2H³³S mutant. Lines represent a nonlinear fit with constrained ¹²⁵I-rMmTX2-parameters (K_d = 0.51 nM and assay concentration 0.2 nM). Note that WT MmTX1, rMmTX1, and rMmTX2 are equally potent in displacing ¹²⁵I-rMmTX2, whereas rMmTx2H³³S is ineffective.