An ECF-type transporter scavenges heme to overcome iron-limitation in Staphylococcus lugdunensis

Abstract

Energy-coupling factor type transporters (ECF) represent trace nutrient acquisition systems. Substrate binding components of ECF-transporters are membrane proteins with extraordinary affinity, allowing them to scavenge trace amounts of ligand. A number of molecules have been described as substrates of ECF-transporters, but an involvement in iron-acquisition is unknown. Host-induced iron limitation during infection represents an effective mechanism to limit bacterial proliferation. We identified the iron-regulated ECF-transporter Lha in the opportunistic bacterial pathogen Staphylococcus lugdunensis and show that the transporter is specific for heme. The recombinant substrate-specific subunit LhaS accepted heme from diverse host-derived hemoproteins. Using isogenic mutants and recombinant expression of Lha, we demonstrate that its function is independent of the canonical heme acquisition system Isd and allows proliferation on human cells as sources of nutrient iron. Our findings reveal a unique strategy of nutritional heme acquisition and provide the first example of an ECF-transporter involved in overcoming host-induced nutritional limitation.

Insights into the bilayer-mediated toppling mechanism of a folate-specific ECF transporter by cryo-EM

“…Moreover, it lays the foundations to further explore the influence of membrane deformations on the transport cycle in ECF transporter complexes within a near native environment. ECF transporter complexes have recently gained renewed attention with the identification of a novel haem transporter belonging to the family of ECF-type ABC transporters (34)(35)(36). As various ECF transporters complexes are encoded in the genome of various human pathogens but not in humans (37,38), it makes them attractive targets for newly designed antimicrobial compounds, for which this work represents a stepping stone towards studying their means of action on a structural level.…”

In vitro reconstitution of dynamically interacting integral membrane subunits of energy-coupling factor transporters

“…It has been proposed that the association of the S-component with and dissociation from the ECF module are steps of the transport mechanism ( Rodionov et al, 2009 ; Henderson et al, 1979a ; Karpowich et al, 2015 ). In the solitary state, the α-helices of S-components adopt a classical transmembrane orientation (approximately perpendicular to the membrane plane) ( Erkens et al, 2011 ; Faustino et al, 2020 ), and the proteins invariably exhibit high affinity for their specific substrates, with low- to subnanomolar K D values ( Erkens et al, 2011 ; Rempel et al, 2019 ; Berntsson et al, 2012 ; Swier et al, 2016 ; Slotboom, 2014 ; Santos et al, 2018 ; Jochim et al, 2020 ; Erkens et al, 2012 ). The high affinity allows them to scavenge scarce substrates from the environment.…”

The repertoire of ABC proteins in Clostridioides difficile

“…1 ii) configurations were the major types of importer identified. However, an SP is not required for ECF-type ABC importers as they contain an S component for capturing solute substrate [14] , [15] , [16] . Few import systems were ECF-type transporters, an example is the cobalt/vitamin uptake system.…”

“…To capture substrates present in the extracellular environment, the SBD-containing protein (SP) facilitates substrate-binding before translocation to the central cavity of TMD. Although an SP is not required for energy-coupling factor (ECF)-type importers [14] , [15] , [16] . ABC importers are important for several biological processes and they appear to be involved in bacterial pathogenesis and virulence.…”