Figure 1: PcTx1–ASIC1 structure and function.
From: Structure of the Acid-sensing ion channel 1 in complex with the gating modifier Psalmotoxin 1
(a) SPR direct binding measurement42 of the interaction of PcTx1 with ASIC1 channels. Green lines depict the SPR response data from a series of PcTx1 concentrations on biotinylated human ASIC1(1-467, top), human ASIC1(residues 25-464, middle) and chicken ASIC1(26-463, bottom) immobilized on a streptavidin coated chip. Black dashed lines indicate the excellent calculated fit of the SPR binding curves using a mathematical one-to-one interaction model. The virtually identical kinetics and binding constants (kon, koff and KD) indicate that PcTx1 binds equally well with an affinity of about 2 nM to the crystallized chicken ASIC1 variant and to electrophysiological functional human ASIC1. (b) Side view of the PcTx1–ASIC1 complex in ribbon representation with the sodium channel subunits in yellow, blue and red and the individual PcTx1 molecules in orange, green and purple. PcTx1 polypeptides are emphasized by transparent surface representation and are bound 50 Å above the membrane at the extracellular domains of ASIC. A putative trapped ion, at the centre of the extracellular domains, is indicated by a purple sphere. The grey lines depict the position of the lipid bilayer based on the hydrophobicity of the protein surface. (c) View from the extracellular space, perpendicular to the membrane and along the three-fold molecular and non-crystallographic symmetry axis. The three PcTx1 molecules bind between adjacent subunits of the ASIC1 homotrimer.
