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The iron-regulated vacuolar Legionella pneumophila MavN protein is a transition-metal transporter.

ABSTRACT: Legionella pneumophila causes a potentially fatal form of pneumonia by replicating within macrophages in the Legionella-containing vacuole (LCV). Bacterial survival and proliferation within the LCV rely on hundreds of secreted effector proteins comprising high functional redundancy. The vacuolar membrane-localized MavN, hypothesized to support iron transport, is unique among effectors because loss-of-function mutations result in severe intracellular growth defects. We show here an iron starvation response by L. pneumophila after infection of macrophages that was prematurely induced in the absence of MavN, consistent with MavN granting access to limiting cellular iron stores. MavN cysteine accessibilities to a membrane-impermeant label were determined during macrophage infections, revealing a topological pattern supporting multipass membrane transporter models. Mutations to several highly conserved residues that can take part in metal recognition and transport resulted in defective intracellular growth. Purified MavN and mutant derivatives were directly tested for transporter activity after heterologous purification and liposome reconstitution. Proteoliposomes harboring MavN exhibited robust transport of Fe²⁺, with the severity of defect of most mutants closely mimicking the magnitude of defects during intracellular growth. Surprisingly, MavN was equivalently proficient at transporting Fe²⁺, Mn²⁺, Co²⁺, or Zn²⁺ Consequently, flooding infected cells with either Mn²⁺ or Zn²⁺ allowed collaboration with iron to enhance intracellular growth of L. pneumophila ?mavN strains, indicating a clear role for MavN in transporting each of these ions. These findings reveal that MavN is a transition-metal-ion transporter that plays a critical role in response to iron limitation during Legionella infection.

SUBMITTER: Christenson ET

PROVIDER: S-EPMC6731752 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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The iron-regulated vacuolar Legionella pneumophila MavN protein is a transition-metal transporter.

Christenson Eric T ET Isaac Dervla T DT Yoshida Karin K Lipo Erion E Kim Jin-Sik JS Ghirlando Rodolfo R Isberg Ralph R RR Banerjee Anirban A

Proceedings of the National Academy of Sciences of the United States of America 20190820 36

Legionella pneumophila causes a potentially fatal form of pneumonia by replicating within macrophages in the Legionella-containing vacuole (LCV). Bacterial survival and proliferation within the LCV rely on hundreds of secreted effector proteins comprising high functional redundancy. The vacuolar membrane-localized MavN, hypothesized to support iron transport, is unique among effectors because loss-of-function mutations result in severe intracellular growth defects. We show here an ...[more]

PMID: 31431530

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Project description:Legionella pneumophila has high iron requirements, and its intracellular growth in human monocytes is dependent on the availability of intracellular iron. To learn more about iron metabolism in L. pneumophila, we have undertaken an analysis of the iron proteins of the bacterium. We first developed an assay to identify proteins by 59Fe labelling and nondenaturing polyacrylamide gel electrophoresis. The assay revealed seven iron proteins (IPs) with apparent molecular weights of 500, 450, 250, 210, 150, 130, and 85. IP150 comigrates with superoxide dismutase activity and is probably the Fe-superoxide dismutase of L. pneumophila. IP210 is the major iron-containing protein (MICP). To identify and characterize MICP, we purified the protein and cloned and sequenced its gene. MICP is a monomeric protein containing 891 amino acids, and it has a calculated molecular mass of 98,147 Da. Analysis of the sequence revealed that MICP has two interesting homologies. First, MICP is highly homologous with the human iron-responsive element-binding protein, consistent with the hypothesis that this critical iron-regulatory molecule of humans has a prokaryotic ancestor. Second, MICP is highly homologous with the Escherichia coli aconitase and to a lesser extent with porcine heart mitochondrial aconitase. Consistent with this, we found that MICP exhibits aconitase activity. In contrast to other aconitases, MICP has a single amino acid change of a potentially deleterious type at a site thought to be critical for substrate binding and enzymatic activity. However, the specific activity of MICP is roughly comparable to that of other aconitases, suggesting that the mutation has at most a mild effect on the aconitase activity of MICP. The abundance of MICP in L. pneumophila suggests either that L. pneumophila requires high aconitase and perhaps tricarboxylic acid cycle activity or that the bacterium requires large amounts of this protein to serve an additional role in bacterial physiology. A need for large amounts of MICP, which contains four Fe atoms per molecule when fully loaded, could at least partly explain L. pneumophila's high metabolic requirement for iron.

Dataset Information

The iron-regulated vacuolar Legionella pneumophila MavN protein is a transition-metal transporter.

Publications

The iron-regulated vacuolar <i>Legionella pneumophila</i> MavN protein is a transition-metal transporter.

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