Bottom-up design of calcium channels from selectivity filters

Abstract

Native ion channels play key roles in biological systems, and engineered versions are widely used as chemogenetic tools and in sensing devices. Protein design has been harnessed to generate pore-containing transmembrane proteins, but the capability to design ion selectivity based on the interactions between ions and selectivity filter residues has been constrained by the lack of methods to place the metal-coordinating residues with atomic-level precision. Here we develop a bottom-up approach to construct Ca2+ channels from selectivity filters with different coordination numbers and different geometries. Patch-clamp experiments show that the designed channels have higher conductance for Ca2+ than for Na+ and other divalent ions (Sr2+ and Mg2+). Cryo-electron microscopy shows that the structure of a designed Ca2+ channel is nearly identical to the design model. Our bottom-up design approach now enables the testing of hypotheses relating filter geometry to ion selectivity and provides a roadmap for creating selective ion channels for a wide range of applications.