1.D.181.  The Synthetic Pore-forming Peptide, pPorA/U (pPor) Family 

Puthumadathil et al. 2022 demonstrated a multi-step structural assembly pathway for alpha-helical peptide pores formed by a 37 amino acid synthetic peptide, pPorU, based on the first 37 aas of the natural porin (PorA; TC# 1.B.59.2.2) from Corynebacterium urealyticum using single-channel electrical recordings. They reported intermediate states during membrane insertion and pore formation of pPorU. The fully assembled pore exhibited large stable conductance, voltage-dependent gating, and functional blockage by cyclic sugars generally applicable to a range of transmembrane pores. They used rationally designed mutants to understand the role of specific amino acids in the assembly of these peptide pores. Mutant peptides that differed from wild-type peptides produced noisy and unstable intermediate states and low conductance pores, demonstrating sequence specificity in the pore-formation process, supported by molecular dynamics simulations. The authors suggested that their study contributed to an understanding of the mechanism of action of naturally occurring alpha-helical pore-forming proteins and should be of broad interest to build peptide-based nanopore sensors (Puthumadathil et al. 2022).

The porinACj is an α-helical porin (TC# 1.B.34.3.1) that is homologous to pPorU and spans the mycolic acid outer membrane of Gram-positive mycolate, Corynebacterium jeikeium. Krishnan R et al. 2019 reported that a 40 aa synthetic peptide, pPorA, corresponding to porin PorACj (TC# 1.B.34.3.1), inserts into the lipid bilayers and forms well-defined pores. By electrical recordings, they measured the single-channel properties that revealed the autonomous assembly of large conductance ion-selective synthetic pores. The pores could be blocked by cyclodextrins of different charge and symmetry. The authors deduced the subunit stoichiometry and putative structure of the pore by site-specific chemical modification in single-channel electrical recordings and gel electrophoresis. They suggested that this is a large functionally uniform transmembrane pore built entirely from short synthetic α-helical peptides. Accordingly, they proposed a model demonstrating structural assembly of large α-helix-based peptide pores for understanding the action of antimicrobial peptides and for the design of pores with applications in biotechnology (Krishnan R et al. 2019).