The uptake of nutrients, including metals, amino acids and peptides are required for many biological processes. Pathogenic bacteria scavenge these essential nutrients from microenvironments to survive within the host. Pathogens must utilize a myriad of mechanisms to acquire these essential nutrients from the host while mediating the effects of toxicity. Bacteria utilize several transport proteins, including ATP-binding cassette (ABC) transporters to import and expel substrates. ABC transporters, conserved across all organisms, are powered by the energy from ATP to move substrates across cellular membranes. In this review, we will focus on nutrient uptake, the role of ABC importers at the host-pathogen interface, and explore emerging therapies to combat pathogenesis. This article is part of a Special Issue entitled: Beyond the Structure-Function Horizon of Membrane Proteins edited by Ute Hellmich, Rupak Doshi and Benjamin McIlwain.

by guest on July 10, 2020 http://www.jbc.org/ Downloaded from Figure 1. Crystal structure of nthiOppA in closed ligand-bound conformation. A, crystal structure of nthiOppA, colored by domain (I A , salmon; I B , wheat; II, cyan), bound to co-purified peptide in green. Inset, surface and stick representation of the co-purified peptide in substrate-binding pocket. B, cartoon representation of the ligand-bound structure of nthiOppA aligned with the open unbound ecOppA structure in gray (PDB code 3TCH), and surface representation of cross-sections of ecOppA and nthiOppA. Based on the alignment with nthiOppA, the green spheres in the open unbound ecOppA structure highlight the binding site where peptide interacts with the SBP to form the closed conformation.

We conclude that the two strands are effectively stapled together through a large number of weak bonds involving T4 ligase. The absence of a similarly strong transformation of DNA in free solution points towards the necessity of parallel pre-alignment through the nanotube. We point to the fact that the formation of hairpins and the 1-d scanning of strands past each other solves the kinetic problem of forming a loop in a maze-like environment.