1.D.158.  The α-Helical Barrel, Cation-selective Pore (HBCP) Family

Scott et al. 2021 used rational de novo design to generate water-soluble alpha-helical barrels with polar interiors, and they confirmed their structures using high-resolution X-ray crystallography. These alpha-helical barrels have water-filled lumens like those of transmembrane channels. They modified the sequences to facilitate their insertion into lipid bilayers. Single-channel electrical recordings and fluorescent imaging of the peptides in membranes showed monodisperse, cation-selective channels of unitary conductance. An X-ray structure solved from the lipidic cubic phase for one peptide revealed an alternative state with tightly packed helices and a constricted channel (Scott et al. 2021). This family is related to TC family 1.D.95, described earlier.

Large transmembrane pores, pPorAs, formed from short synthetic alpha-helical peptides of tunable conductance and selectivity for single-molecule sensing of peptides have been synthesized (R et al. 2020). The selective translocation kinetics of differently charged cationic and anionic peptides were measured at single-molecule resolution. The charged peptides were electrophoretically pulled into the pores, resulting in an increase in the dissociation rate with voltage, indicating successful translocation of the peptides. The charge pattern lining the pore lumen and the orientation of the pores in the membrane based on the asymmetry in the peptide-binding kinetics were determined. The salt and pH-dependent measurements confirmed the electrostatic dominance and charge selectivity in controlling target peptide interactions with the pores. Remarkably, The selectivity of the pores to charged peptides was tuned by modifying the charge composition of the pores, thus establishing the molecular and electrostatic basis of peptide translocation. Thus, these synthetic pores selectively conduct specific ions and biomolecules, an advantage for nanopore proteomics analysis and synthetic nanobiotechnology applications (R et al. 2020).