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The S. mutans mntE gene encodes a manganese efflux transporter.

ABSTRACT: Streptococcus mutans is a colonizer of the human dentition, and under conditions of dysbiosis is the primary causative agent of dental caries. The pathogenic potential of S. mutans depends, in part, on its ability to regulate the transport of metal ions across the plasma membrane to maintain intracellular metal ion homeostasis. Research in our laboratory has focused on the Mn²⁺ -specific SloC lipoprotein importer and its regulator encoded by the S. mutans sloR gene. Herein, we used a bioinformatics approach to identify a gene on the S. mutans UA159 chromosome, SMU_1176, as a metal ion efflux transporter that contributes to S. mutans manganese ion homeostasis. Metal ion sensitivity assays performed with the wild-type S. mutans UA159 strain and an isogenic SMU_1176 insertion-deletion mutant, called GMS3000, revealed significantly heightened sensitivity of GMS3000 to MnSO₄ challenge. ⁵⁴ Mn uptake experiments support the accumulation of ⁵⁴ Mn in GMS3000 cell pellets when compared to ⁵⁴ Mn concentrations in UA159 or in a complemented strain of GMS3000, called GMS3001. Inductively coupled plasma mass spectrometry (ICP-MS) studies were performed in parallel to quantify intracellular manganese concentrations in these strains, the results of which corroborate the ⁵⁴ Mn uptake studies, and support the SMU_1176 gene product as a Mn²⁺ efflux protein. Expression profiling experiments revealed de-repression of SMU_1176 gene transcription in the SloR-deficient GMS584 strain of S. mutans, especially under high manganese conditions. In conclusion, the S. mutans SMU_1176 gene, which we renamed mntE, is a manganese efflux transporter that contributes to essential metal ion homeostasis as part of the SloR regulon.

SUBMITTER: O'Brien J

PROVIDER: S-EPMC8212816 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The activity of the manganese (Mn) efflux transporter SLC30A10 in the liver and intestines is critical for Mn excretion and preventing Mn toxicity. Homozygous loss-of-function mutations in SLC30A10 are a well-established cause of hereditary Mn toxicity. But, the relationship between more common SLC30A10 polymorphisms, Mn homeostasis, and disease is only recently emerging. In 2021, the first coding SNP in SLC30A10 (T95I) was associated with liver disease raising the hypothesis that the T95I substitution may induce disease by inhibiting the Mn efflux function of SLC30A10. Here, we test this hypothesis using structural, viability, and metal quantification approaches. Analyses of a predicted structure of SLC30A10 revealed that the side chain of T95 pointed away from the putative Mn-binding cavity, raising doubts about the impact of the T95I substitution on SLC30A10 function. In HeLa or HepG2 cells, overexpression of SLC30A10-WT or T95I resulted in comparable reductions of intracellular Mn levels and protection against Mn-induced cell death. Furthermore, ΔSLC30A10 HepG2 cells, generated using CRISPR/Cas9, exhibited elevated Mn levels and heightened sensitivity to Mn-induced cell death, and these phenotypic changes were similarly rescued by expression of SLC30A10-WT or T95I. Finally, turnover rates of SLC30A10-WT or T95I were also comparable. In summary, our results indicate that the Mn transport activity of SLC30A10-T95I is essentially comparable to the WT protein. Our findings imply that SLC30A10-T95I either has a complex association with liver injury that extends beyond the simple reduction in SLC30A10 activity or alternatively the T95I mutation lacks a causal role in liver disease.NEW & NOTEWORTHY This study demonstrates that the T95I polymorphism in the manganese transporter SLC30A10, which has been associated with liver disease in human GWAS studies, does not impact transporter function in cell culture. These findings raise doubts about the causal relationship of the T95I polymorphism with human disease and highlight the importance of validating GWAS findings using mechanistic approaches.

Project description:Manganese (Mn) is an essential micronutrient critical for the pathogenesis of Staphylococcus aureus, a significant cause of human morbidity and mortality. Paradoxically, excess Mn is toxic; therefore, maintenance of intracellular Mn homeostasis is required for survival. Here we describe a Mn exporter in S. aureus, MntE, which is a member of the cation diffusion facilitator (CDF) protein family and conserved among Gram-positive pathogens. Upregulation of mntE transcription in response to excess Mn is dependent on the presence of MntR, a transcriptional repressor of the mntABC Mn uptake system. Inactivation of mntE or mntR leads to reduced growth in media supplemented with Mn, demonstrating MntE is required for detoxification of excess Mn. Inactivation of mntE results in elevated levels of intracellular Mn, but reduced intracellular iron (Fe) levels, supporting the hypothesis that MntE functions as a Mn efflux pump and Mn efflux influences Fe homeostasis. Strains inactivated for mntE are more sensitive to the oxidants NaOCl and paraquat, indicating Mn homeostasis is critical for resisting oxidative stress. Furthermore, mntE and mntR are required for full virulence of S. aureus during infection, suggesting S. aureus experiences Mn toxicity in vivo Combined, these data support a model in which MntR controls Mn homeostasis by balancing transcriptional repression of mntABC and induction of mntE, both of which are critical for S. aureus pathogenesis. Thus, Mn efflux contributes to bacterial survival and virulence during infection, establishing MntE as a potential antimicrobial target and expanding our understanding of Mn homeostasis.IMPORTANCE Manganese (Mn) is generally viewed as a critical nutrient that is beneficial to pathogenic bacteria due to its function as an enzymatic cofactor and its capability of acting as an antioxidant; yet paradoxically, high concentrations of this transition metal can be toxic. In this work, we demonstrate Staphylococcus aureus utilizes the cation diffusion facilitator (CDF) family protein MntE to alleviate Mn toxicity through efflux of excess Mn. Inactivation of mntE leads to a significant reduction in S. aureus resistance to oxidative stress and S. aureus-mediated mortality within a mouse model of systemic infection. These results highlight the importance of MntE-mediated Mn detoxification in intracellular Mn homeostasis, resistance to oxidative stress, and S. aureus virulence. Therefore, this establishes MntE as a potential target for development of anti-S. aureus therapeutics.

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The S. mutans mntE gene encodes a manganese efflux transporter.

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