Spider Toxin SNX-482 Gating Modifier Spontaneously Partitions in the Membrane Guided by Electrostatic Interactions

Spider toxin SNX-482 is a cysteine-rich peptide that interferes with calcium channel activity by binding to voltage-sensing domains of the Ca_V2.3 subtype. Two mechanisms dominate the binding process of cysteine-rich peptides: direct binding from the aqueous phase or through lateral diffusion from the membrane, the so-called reduction in dimensionality mechanism. In this work, via coarse-grained and atomistic molecular dynamics simulations, we have systematically studied the spontaneous partitioning of SNX-482 with membranes of different anionic compositions and explored via diffusional analysis both binding mechanisms. Our simulations revealed a conserved protein patch that inserts in the membrane, a preference for binding towards partially negatively charged membranes, and that electrostatics guides membrane binding by incrementing and aligning the molecular dipole. Finally, diffusivity calculations showed that the toxin diffusion along the membrane plane is an order of magnitude slower than the aqueous phase suggesting that the critical factor in determining the SNX-482-Ca_V2.3 binding mechanism is the affinity between the membrane and SNX-482.