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Review
. 2017 Jul 19;9(7):840-851.
doi: 10.1039/c7mt00112f.

Ferrous iron efflux systems in bacteria

Hualiang Pi  1 , John D Helmann
Affiliations
Review

Ferrous iron efflux systems in bacteria

Hualiang Pi et al. Metallomics. .

Abstract

Bacteria require iron for growth, with only a few reported exceptions. In many environments, iron is a limiting nutrient for growth and high affinity uptake systems play a central role in iron homeostasis. However, iron can also be detrimental to cells when it is present in excess, particularly under aerobic conditions where its participation in Fenton chemistry generates highly reactive hydroxyl radicals. Recent results have revealed a critical role for iron efflux transporters in protecting bacteria from iron intoxication. Systems that efflux iron are widely distributed amongst bacteria and fall into several categories: P1B-type ATPases, cation diffusion facilitator (CDF) proteins, major facilitator superfamily (MFS) proteins, and membrane bound ferritin-like proteins. Here, we review the emerging role of iron export in both iron homeostasis and as part of the adaptive response to oxidative stress.

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Figures

fig. 1
fig. 1. Iron homeostasis in bacteria
Under iron deficient conditions (left), high affinity iron uptake systems are induced to scavenge iron from the surroundings to maintain the cell's labile iron pool. when iron is limiting, it is selectively partitioned to the most essential functions and incorporation into lower priority iron enzymes is translationally inhibited as part of an iron sparing response. in many cases, iron-independent enzymes may be derepressed to replace functions that would otherwise depend on iron. under iron excess conditions, the cell will have a full complement of iron-requiring enzymes, and iron in excess of immediate needs will be either stored for future use or exported by fe2+ efflux transporters to prevent iron overload.
fig. 2
fig. 2. Ferrous iron efflux systems in bacteria
Four different groups of transporters can function as fe2+ efflux pumps. i. p1b-atpase; ii. cation diffusion facilitator (cdf); iii. major facilitator superfamily (mfs); iv. membrane-bound ferritin. a typical p1b-atpase consists of a transmembrane domain (tmd) that has 6–8 helices, a soluble actuator domain (not shown), and an atp-binding domain (atp-bd). a cdf transporter contains a n-terminal domain (ntd), a transmembrane domain (tmd) that has 6 helices, a histine-rich interconnecting loop (il) between tm4 and tm5 (not shown), and a c-terminal cytoplasmic domain (ctd). the common structural fold (mfs fold) of a mfs transporter is composed of two distinct domains, n domain and c domain. each domain has six consecutive transmembrane helices. a membrane-bound ferritin transporter has two major domains, n-terminal ferritin-like or er domain (er) and c-terminal membrane-embedded vacuolar iron transporter domain (vit1).
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