MIIM30011 Bacterial Metal Ion Acquisition Lecture 2024 PDF

 Bacterial metal ion acquisition Bacterial metal ion acquisition MIIM30011 Dr Stephanie Neville MIIM30011 [email protected] Dr Stephanie Neville Learning objectives Knowledge of key mechanisms of host n...

 Bacterial metal ion acquisition Bacterial metal ion acquisition MIIM30011 Dr Stephanie Neville MIIM30011 [email protected] Dr Stephanie Neville Learning objectives Knowledge of key mechanisms of host nutritional immunity Understanding of bacterial strategies for acquiring essential micronutrients during infection and relevance for disease outcome Appreciation of how essentiality shapes competitive evolution between host and pathogen Roadmap to disease 1) Enter the body 2) Colonise the host 3) Evade host defences 4) Multiply and disseminate 5) Cause damage to the host Biology needs metals! Metal ions facilitate the chemistry that supports life Up to 50% of all cellular proteins require a metal cofactor Structural cofactors: Maintain protein conformational stability Functional cofactors: Lowering activation energy for chemical reactions Electron transfer and redox reactions Metals are essential for life Manganese Oxidative stress tolerance (MnSOD) Natural competence Iron DNA replication Cell division Copper Cellular energy production Oxidative stress tolerance (Cu/ZnSOD) Zinc Carbon source metabolism Structural & functional metalloprotein cofactor The pathogen conundrum Strictly host-adapted pathogens do not have an environmental reservoir Where do bacteria get their essential micronutrients (metal ions)? Steal them from the host Nutritional Immunity Yuki, Marei et al; 2019 https://doi.org/10.1038/s41564-019-0484-8 - Behind the paper Host modulation (sequestration) of essential micronutrients to restrict pathogen acquisition, resulting in reduced virulence and viability of the bacteria Host mechanisms of nutritional immunity All essential metal ions in the host are sequestered! 1) Limit extracellular abundance 2) Secrete metal- binding molecules 3) Direct inactivation of bacterial metal acquisition molecules Surviving the starvation Extracellular metal ion abundance as environmental cues Anatomical niche specific Modulation of bacterial gene expression Activation of alternative, metal-independent pathways Metal ion acquisition pathways are crucial virulence determinants Mechanisms of bacterial metal ion scavenging 1. Lysis of host cells 2. Direct acquisition of host proteins 3. Secreted molecules 4. Direct acquisition of metal ions Bacterial cytoplasm Mechanisms of bacterial metal ion scavenging 1. Lysis of host cells 2. Direct acquisition of host proteins 3. Secreted molecules 4. Direct acquisition of metal ions Bacterial cytoplasm 1. Lysis of host cells Common iron (Fe) acquisition strategy Primarily targets erythrocytes Utilised by multiple pathogenic species Pseudomonas, Staphylococci, Streptococci & Escherichia Requires the release of haemolysins Fe-regulated surface determinant (Isd) system First described in Staphylococcus aureus Consists of 10 genes Cell wall-anchored proteins (IsdABCH) Membrane transport system (IsdDEF) Haem oxygenases (IsdG & IsdI) Transpeptidase (SrtB) Essential for full virulence of numerous bacterial species Grigg et al, 2010 doi.org/10.1016/j.jinorgbio.2009.09.012 Mechanisms of bacterial metal ion scavenging 1. Lysis of host cells 2. Direct acquisition of host proteins 3. Secreted molecules 4. Direct acquisition of metal ions 2. Direct acquisition of host proteins Host proteins bind metal ions with incredibly high affinity Serum transferrin Kf ~1036 for Fe(III) Expression is up-regulated during infection Why compete when you can steal! High affinity membrane-bound receptors Highly abundant on the cell surface Capture host proteins (transferrin/lactoferrin) for transport Metal ion (Fe) is released in the cytoplasm Transferrin binding protein A (TbpA) Found in numerous human pathogens including Neisseria and Haemophilus spp. Able to directly acquire Fe(III)-bound transferrin from the host TbpA driving rapid evolution of transferrin Transferrin (human) TbpA (Neisseria) TbpA (Haemophilus) Barber & Elde, 2014 DOI: (10.1126/science.1259329) Mechanisms of bacterial metal ion scavenging 1. Lysis of host cells 2. Direct acquisition of host proteins 3. Secreted molecules 4. Direct acquisition of metal ions 3. Secreted molecules Released into the extracellular environment by bacterial pathogens Directly compete with host proteins for metal ions Recovered by any bacteria with the correct receptor/transporter Often cargo or compound must be modified to liberate cargo Siderophores Metallophores  Siderophores Iron carriers >500 compounds identified Belong to multiple, structurally-distinct classes Low molecular weight compounds 500-1500 Daltons Primarily synthesised by non-ribosomal peptide synthetases (NRPSs) Hydroxamates Enzymatically driven Catecholates Regulated by intracellular Fe abundance Fe-responsive transcriptional regulator, Fur Not considered to be associated with acquisition of other metal ions Formation constant (Kf) >1030 for Fe(III) Schalk et al, 2011 doi.org/10.1111/j.1462-2920.2011.02556.x The siderophore arms race Enterobactin synthesised by Enterobacteriaceae family Captured by host siderocalins (lipocalin-2) Secreted by neutrophils and epithelial cells during inflammation Potent antimicrobial activity Glycosylated derivatives (salmochelin) can no longer be bound by lipocalin-2. à Continued virulence in the presence of lipocalin-2 Enterobactin Salmochelin Bister et al., 2004 doi.org/10.1023/B:BIOM.0000029432.69418.6a Metallophores Commonly nicotianamine derivatives Originally identified in plants Nicotianamine Enzymatically synthesised by nicotianamine synthase (NAS) Broad specificity for divalent cations Cu(II) > Ni(II) > Co(II) > Zn(II) > Fe(II) Not regulated by cellular Fe abundance First full characterisation of a bacterial metallophore system in 2016 Cnt system in Staphylococcus aureus Cnt system Termed the ‘Staphylopine’ system First report showed association with numerous metal ions Staphylopine Subsequent studies have confirmed regulation primarily by cellular zinc levels Able to compete with host protein Calprotectin for zinc binding (pM-fM affinity) Consequences for promiscuous ligand binding Ghssein et al. 2016 DOI: 10.1126/science.aaf1018 Mechanisms of bacterial metal ion scavenging 1. Lysis of host cells 2. Direct acquisition of host proteins 3. Secreted molecules 4. Direct acquisition of metal ions 4. Direct acquisition of metal ions High affinity metal ion transporters Must be able to acquire metals directly from the host ATP binding cassette (ABC) transporters Comprised of integral membrane channel Substrate binding protein Selectively acquire metals ions from host environment Must achieve specificity for cognate ligand and exclude chemically similar metals Must be able to bind and release ligand in the absence of energy Essential for virulence Pneumococcal Surface Adhesin A (PsaA) Discovered in 1990s as a critical virulence determinant for Streptococcus pneumoniae High affinity manganese (Mn) binding protein PsaBCA ABC transporter Removal of any component results in complete attenuation of virulence W T saB saC psaA Δp Δp Δ Adapted from McAllister et al., 2004 Mol. Micro. Pneumococcal Surface Adhesin A (PsaA) Achieving selectivity for Mn over Zn is chemically complicated Same coordinating ligands (O and N) are used for both PsaA binds both Mn and Zn with nM affinity Crystal structures were largely super-imposable How does PsaA function in only Mn recruitment? Zn-bound (1PSZ) Mn-bound (3ZTT) Lawrence et al., 1998 McDevitt et al., 2011  Pneumococcal Surface Adhesin A (PsaA) Reversibility! Once bound, PsaA is unable to release zinc to the transporter Prevents erroneous transport of non-cognate metal ions PsaA can be inhibited by zinc Zinc is an antimicrobial agent Counago et al., 2014 Therapeutic targeting of metal uptake pathways Metal ion acquisition pathways are essential for bacteria viability and virulence Widely conserved within a species (core genome) Genetic variation is not well tolerated evolutionarily Metal binding proteins are often: Extracellularly located Highly immunogenic To inhibit or vaccinate? Inhibitors Exploiting the specificity of bacterial Fe(III) binding proteins (siderophores) with Ga(III) Showed efficacy against multiple ESKAPE pathogens (S. aureus, A. baumannii, P. aeruginosa) in vitro and in vivo Ga(III) compounds already FDA approved Issues with bioavailability, solubility, off-targets effects (immunosuppression) Research is on-going Antibody-mediated inhibition of haem uptake through inhibition of IsdA and IsdB Prevents haem utilisation as a source of Fe Efficacious in vitro and in vivo against S. aureus To inhibit or vaccinate? Vaccinate Targeting zinc uptake pathways (ZnuD) Neisseria meningitidis and Acinetobacter baumannii Upregulated during host-imposed zinc starvation Hesse et al., 2019 doi.org/10.1128/IAI.00746-19 Shown modest efficacy in reducing bacterial burden during infection Targeting manganese uptake pathways (PsaA) Streptococcus pneumoniae – all serotypes Current vaccines are serotype-dependent (23 of >100 covered) Often requires multiple protein antigens to be used Efficacy limited by capsule Yu et al., 2018 doi.org/10.1128/IAI.00916-17 Summary Metal ions are an essential micronutrient for all forms of life Metal acquisition pathways are crucial for the viability of all organisms Competition at the host-pathogen interface can determine disease outcome Driven evolutionary selective pressure for metal binding proteins/metallophores Near complete conservation and prevalence of these systems renders them good therapeutic targets Many studies showing in vitro and in vivo efficacy, comparatively few clinical trials References Grigg et al., 2010. Structural biology of heme binding in the Staphylococcus aureus Isd system, Journal of Inorganic Biochemistry, Volume 104, Issue 3, Pages 341-348 https://doi.org/10.1016/j.jinorgbio.2009.09.012 Yu et al., 2018. Comparison of immunogenicity and protection of two pneumococcal protein vaccines based on PsaA and PspA. Infection and Immunity 86:e00916-17. https:// doi.org/10.1128/IAI.00916-17. Ghssein et al., 2016. Biosynthesis of a broad-spectrum nicotianamine-like metallophore in Staphylococcus aureus. Science 1105 – 1109 https://doi.org/10.1126/science.aaf1018 Minandri et al., 2014. Promises and failures of gallium as an antibacterial agent. Future Microbiology 9(3), 379–397 https://doi.org/ 10.2217/FMB.14.3 Counago et al., 2014 Imperfect coordination chemistry facilitates metal ion release in the Psa permease. Nature Chemical Biology 10, 35– 41 https://doi.org/10.1038/nchembio.1382 Laffont et al., 2020 The ancient roots of nicotianamine: diversity, role, regulation and evolution of nicotianamine-like Metallophores. Metallomics 12 (10) 1480–1493, https://doi.org/10.1039/d0mt00150c Schalk et al., 2011. New roles for bacterial siderophores in metal transport and tolerance. Environmental Microbiology, 13: 2844 2854. https://doi.org/10.1111/j.1462-2920.2011.02556.x Hesse et al. 2019. The Acinetobacter baumannii Znu system overcomes host-imposed nutrient zinc limitation. Infect Immun 87:e00746- 19. https://doi.org/10.1128/IAI.00746-19. Murdoch and Skaar, 2022 Nutritional immunity: the battle for nutrient metals at the host–pathogen interface. Nat Rev Microbiol 20, 657–670. https://doi.org/10.1038/s41579-022-00745-6 Bister et al., 2004. The structure of salmochelins: C-glucosylated enterobactins of Salmonella enterica. Biometals 17, 471–48 https://doi.org/10.1023/B:BIOM.0000029432.69418.6a McDevitt et al. 2011 A Molecular Mechanism for Bacterial Susceptibility to Zinc. PLOS Pathogens 7(11): e1002357. https://doi.org/10.1371/journal.ppat.1002357 McAllister et al. 2004 Molecular analysis of the psa permease complex of Streptococcus pneumoniae. Mol Microbiol 53: 889–901. Barber & Elde 2014 Escape from bacterial iron piracy through rapid evolution of transferrin. Science 1362 – 1366 https://doi.org/10.1126/science.1259329