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Energy coupling factor (ECF) transporters are responsible for the uptake of micronutrients in bacteria and archaea. They consist of an integral membrane unit, the S-component, and a tripartite ECF module. It has been proposed that the S-component mediates the substrate transport by toppling over in the membrane when docking onto an ECF module. Here, we present multi-scale molecular dynamics simulations and in vitro experiments to study the molecular toppling mechanism of the S-component of a folate-specific ECF transporter. Simulations reveal a strong bending of the membrane around the ECF module that provides a driving force for toppling of the S-component. The stability of the toppled state depends on the presence of non-bilayer forming lipids, as confirmed by folate transport activity measurements. Together, our data provide evidence for a lipid-dependent toppling-based mechanism for the folate-specific ECF transporter, a mechanism that might apply to other ECF transporters., Energy coupling factor (ECF) transporters are responsible for the uptake of micronutrients and consist of an integral membrane unit, the S-component, which confers substrate specificity. Here, authors present multi-scale molecular dynamics simulations and in vitro experiments to study the molecular toppling mechanism of the S-component of a folate-specific ECF transporter.

Energy-coupling factor (ECF)-type ATP-binding cassette (ABC) transporters catalyze membrane transport of micronutrients in prokaryotes. Crystal structures and biochemical characterization have revealed that ECF transporters are mechanistically distinct from other ABC transport systems. Notably, ECF transporters make use of small integral membrane subunits (S-components) that are predicted to topple over in the membrane when carrying the bound substrate from the extracellular side of the bilayer to the cytosol. Here, we review the phylogenetic diversity of ECF transporters as well as recent structural and biochemical advancements that have led to the postulation of conceptually different mechanistic models. These models can be described as power stroke and thermal ratchet. Structural data indicate that the lipid composition and bilayer structure are likely to have great impact on the transport function. We argue that study of ECF transporters could lead to generic insight of membrane protein structure, dynamics, and interaction. Expected final online publication date for the Annual Review of Biochemistry Volume 88 is June 20, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Here, we report on the virtual screening, design, synthesis and structure–activity relationships (SARs) of the first class of selective, antibacterial agents against the energy-coupling factor (ECF) transporters. The ECF transporters are a family of transmembrane proteins involved in the uptake of vitamins in a wide range of bacteria. Inhibition of the activity of these proteins could reduce the viability of pathogens that depend on vitamin uptake. Because of their central role in the metabolism of bacteria and their absence in humans, ECF transporters are novel potential antimicrobial targets to tackle infection. The hit compound’s metabolic and plasma stability, the potency (20, MIC Streptococcus pneumoniae = 2 µg/mL), the absence of cytotoxicity and a lack of resistance development under the conditions tested here suggest that this scaffold may represent a promising starting point for the development of novel antimicrobial agents with an unprecedented mechanism of action.

Energy coupling factor (ECF) transporters take up micronutrients in Bacteria and Archaea. They consist of a membrane-embedded S-component that provides substrate specificity and a three-subunit ECF module that couples ATP hydrolysis to transport. The S-components ThiT (for thiamin) and NiaX (for niacin) from Lactococcus lactis form complexes with the same ECF module. Here, we assayed the uptake of thiamin and niacin in Escherichia coli cells expressing the transporter genes. We demonstrate that the two different S-components compete for the ECF module, and that competition is more efficient in the presence of the transported substrate. The data suggest that binding and release of the S-components is a step in the transport cycle.