scholarly journals Redirection of Metabolism in Response to Fatty Acid Kinase inStaphylococcus aureus

2018 ◽  
Vol 200 (19) ◽  
Author(s):  
Zachary DeMars ◽  
Jeffrey L. Bose
Keyword(s):  
Amino Acids ◽  
Staphylococcus Aureus ◽  
Fatty Acid ◽  
Amino Acid ◽  
Virulence Factor ◽  
Tca Cycle ◽  
Acetate Metabolism ◽  
Adenylate Energy Charge ◽  
Wild Type ◽  
Content Type

ABSTRACTStaphylococcus aureusis capable of phosphorylating exogenous fatty acids for incorporation into the bacterium's membrane via the fatty acid kinase, FakA. Additionally, FakA plays a significant role in virulence factor regulation and skin infections. We previously showed that afakAmutant displays altered growth kineticsin vitro, observed during the late-exponential phase of growth. Here, we demonstrate that the absence of FakA leads to key metabolic changes. First, thefakAmutant has an altered acetate metabolism, with acetate being consumed at an increased rate than in the wild-type strain. Moreover, the growth benefit was diminished with inactivation of the acetate-generating enzyme AckA. Using a mass spectrometry-based approach, we identified altered concentrations of tricarboxylic acid (TCA) cycle intermediates and both intracellular and extracellular amino acids. Together, these data demonstrate a change in carbohydrate carbon utilization and altered amino acid metabolism in thefakAmutant. Energy status analysis revealed the mutant had a similar ADP/ATP ratio to that of the wild type, but a reduced adenylate energy charge. The inactivation offakAchanged the NAD+/NADH and NADP+/NADPH ratios, indicating a more oxidized cellular environment. Evidence points to the global metabolic regulatory proteins CcpA and CodY being important contributors to the altered growth in afakAmutant. Indeed, it was found that directing amino acids from the urea cycle into the TCA cycle via glutamate dehydrogenase was an essential component ofS. aureusgrowth after glucose depletion. Together, these data identify a previously unidentified role of FakA in the global physiology ofS. aureus, linking external fatty acid utilization and central metabolism.IMPORTANCEThe fatty acid kinase, FakA, ofStaphylococcus aureusplays several important roles in the cell. FakA is important for the activation of the SaeRS two-component system and secreted virulence factors like α-hemolysin. However, the contribution of FakA to cellular metabolism has not been explored. Here, we highlight the metabolic consequence of removal of FakA from the cell. The absence of FakA leads to altered acetate metabolism and altered redox balance, as well as a change in intracellular amino acids. Additionally, the use of environmental amino acid sources is affected by FakA. Together, these results demonstrate for the first time that FakA provides a link between the pathways for exogenous fatty acid use, virulence factor regulation, and other metabolic processes.

scholarly journals MetR-Regulated Vibrio cholerae Metabolism Is Required for Virulence

mBio ◽  
2012 ◽  
Vol 3 (5) ◽  
Author(s):  
Ryan W. Bogard ◽  
Bryan W. Davies ◽  
John J. Mekalanos
Keyword(s):  
Amino Acid ◽  
Vibrio Cholerae ◽  
Virulence Factor ◽  
Current Knowledge ◽  
Intestinal Colonization ◽  
Wild Type ◽  
Pathogenic Potential ◽  
Content Type ◽  
Mouse Intestine

ABSTRACTLysR-type transcriptional regulators (LTTRs) are the largest, most diverse family of prokaryotic transcription factors, with regulatory roles spanning metabolism, cell growth and division, and pathogenesis. Using a sequence-defined transposon mutant library, we screened a panel ofV. choleraeEl Tor mutants to identify LTTRs required for host intestinal colonization. Surprisingly, out of 38 LTTRs, only one severely affected intestinal colonization in the suckling mouse model of cholera: the methionine metabolism regulator, MetR. Genetic analysis of genes influenced by MetR revealed thatglyA1andmetJwere also required for intestinal colonization. Chromatin immunoprecipitation of MetR and quantitative reverse transcription-PCR (qRT-PCR) confirmed interaction with and regulation ofglyA1, indicating that misregulation ofglyA1is likely responsible for the colonization defect observed in themetRmutant. TheglyA1mutant was auxotrophic for glycine but exhibited wild-type trimethoprim sensitivity, making folate deficiency an unlikely cause of its colonization defect. MetJ regulatory mutants are not auxotrophic but are likely altered in the regulation of amino acid-biosynthetic pathways, including those for methionine, glycine, and serine, and this misregulation likely explains its colonization defect. However, mutants defective in methionine, serine, and cysteine biosynthesis exhibited wild-type virulence, suggesting that these amino acids can be scavenged in vivo. Taken together, our results suggest that glycine biosynthesis may be required to alleviate an in vivo nutritional restriction in the mouse intestine; however, additional roles for glycine may exist. Irrespective of the precise nature of this requirement, this study illustrates the importance of pathogen metabolism, and the regulation thereof, as a virulence factor.IMPORTANCEVibrio choleraecontinues to be a severe cause of morbidity and mortality in developing countries. Identification ofV. choleraefactors critical to disease progression offers the potential to develop or improve upon therapeutics and prevention strategies. To increase the efficiency of virulence factor discovery, we employed a regulator-centric approach to multiplex our in vivo screening capabilities and allow whole regulons inV. choleraeto be interrogated for pathogenic potential. We identified MetR as a new virulence regulator and serine hydroxymethyltransferase GlyA1 as a new MetR-regulated virulence factor, both required byV. choleraeto colonize the infant mouse intestine. Bacterial metabolism is a prerequisite to virulence, and current knowledge of in vivo metabolism of pathogens is limited. Here, we expand the known role of amino acid metabolism and regulation in virulence and offer new insights into the in vivo metabolic requirements ofV. choleraewithin the mouse intestine.

scholarly journals A Novelmeso-Diaminopimelate Dehydrogenase from Symbiobacterium thermophilum: Overexpression, Characterization, and Potential for d-Amino Acid Synthesis

2012 ◽  
Vol 78 (24) ◽  
pp. 8595-8600 ◽  
Author(s):  
Xiuzhen Gao ◽  
Xi Chen ◽  
Weidong Liu ◽  
Jinhui Feng ◽  
Qiaqing Wu ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Substrate Specificity ◽  
Enantiomeric Excess ◽  
Acid Synthesis ◽  
Amino Acid Residues ◽  
Wild Type ◽  
Gene Encoding ◽  
Amino Acid Synthesis ◽  
Content Type

ABSTRACTmeso-Diaminopimelate dehydrogenase (meso-DAPDH) is an NADP+-dependent enzyme which catalyzes the reversible oxidative deamination on thed-configuration ofmeso-2,6-diaminopimelate to producel-2-amino-6-oxopimelate. In this study, the gene encoding ameso-diaminopimelate dehydrogenase fromSymbiobacterium thermophilumwas cloned and expressed inEscherichia coli. In addition to the native substratemeso-2,6-diaminopimelate, the purified enzyme also showed activity towardd-alanine,d-valine, andd-lysine. This enzyme catalyzed the reductive amination of 2-keto acids such as pyruvic acid to generated-amino acids in up to 99% conversion and 99% enantiomeric excess. Sincemeso-diaminopimelate dehydrogenases are known to be specific tomeso-2,6-diaminopimelate, this is a unique wild-typemeso-diaminopimelate dehydrogenase with a more relaxed substrate specificity and potential ford-amino acid synthesis. The enzyme is the most stablemeso-diaminopimelate dehydrogenase reported to now. Two amino acid residues (F146 and M152) in the substrate binding sites ofS. thermophilum meso-DAPDH different from the sequences of other knownmeso-DAPDHs were replaced with the conserved amino acids in othermeso-DAPDHs, and assay of wild-type and mutant enzyme activities revealed that F146 and M152 are not critical in determining the enzyme's substrate specificity. The high thermostability and relaxed substrate profile ofS. thermophilum meso-DAPDH warrant it as an excellent starting enzyme for creating effectived-amino acid dehydrogenases by protein engineering.

scholarly journals Vibrio fischeriDarR Directs Responses to D-Aspartate and Represents a Group of Similar LysR-Type Transcriptional Regulators

2018 ◽  
Vol 200 (15) ◽  
Author(s):  
Richard M. Jones ◽  
David L. Popham ◽  
Alicia L. Schmidt ◽  
Ellen L. Neidle ◽  
Eric V. Stabb
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Transcriptional Control ◽  
Vibrio Fischeri ◽  
Transcriptional Response ◽  
Control Mechanisms ◽  
Wild Type ◽  
Acinetobacter Baylyi ◽  
Transcriptional Responses ◽  
Content Type

ABSTRACTMounting evidence suggests thatd-amino acids play previously underappreciated roles in diverse organisms. In bacteria, evend-amino acids that are absent from canonical peptidoglycan (PG) may act as growth substrates, as signals, or in other functions. Given these proposed roles and the ubiquity ofd-amino acids, the paucity of knownd-amino-acid-responsive transcriptional control mechanisms in bacteria suggests that such regulation awaits discovery. We found that DarR, a LysR-type transcriptional regulator (LTTR), activates transcription in response tod-Asp. Thed-Glu auxotrophy of aVibrio fischerimurI::Tn mutant was suppressed, with the wild-type PG structure maintained, by a point mutation indarR. ThisdarRmutation resulted in the overexpression of an adjacent operon encoding a putative aspartate racemase, RacD, which compensated for the loss of the glutamate racemase encoded bymurI. Using transcriptional reporters, we found that wild-type DarR activatedracDtranscription in response to exogenousd-Asp but not upon the addition ofl-Asp,l-Glu, ord-Glu. A DNA sequence typical of LTTR-binding sites was identified betweendarRand the divergently orientedracDoperon, and scrambling this sequence eliminated activation of the reporter in response tod-Asp. In several proteobacteria, genes encoding LTTRs similar to DarR are linked to genes with predicted roles ind- and/orl-Asp metabolism. To test the functional similarities in another bacterium,darRandracDmutants were also generated inAcinetobacter baylyi. InV. fischeriandA. baylyi, growth ond-Asp required the presence of bothdarRandracD. Our results suggest that multiple bacteria have the ability to sense and respond tod-Asp.IMPORTANCEd-Amino acids are prevalent in the environment and are generated by organisms from all domains of life. Although some biological roles ford-amino acids are understood, in other cases, their functions remain uncertain. Given the ubiquity ofd-amino acids, it seems likely that bacteria will initiate transcriptional responses to them. Elucidatingd-amino acid-responsive regulators along with the genes they control will help uncover bacterial uses ofd-amino acids. Here, we report the discovery of DarR, a novel LTTR inV. fischerithat mediates a transcriptional response to environmentald-Asp and underpins the catabolism ofd-Asp. DarR represents the founding member of a group of bacterial homologs that we hypothesize control aspects of aspartate metabolism in response tod-Asp and/or tod-Asp-containing peptides.

scholarly journals VfrB Is a Key Activator of the Staphylococcus aureus SaeRS Two-Component System

2016 ◽  
Vol 199 (5) ◽  
Author(s):  
Christina N. Krute ◽  
Kelly C. Rice ◽  
Jeffrey L. Bose
Keyword(s):  
Staphylococcus Aureus ◽  
Fatty Acid ◽  
Virulence Factors ◽  
Virulence Factor ◽  
Class I ◽  
Exponential Growth Phase ◽  
Two Component System ◽  
Component System ◽  
Content Type ◽  
Two Component

ABSTRACT In previous studies, we identified the fatty acid kinase virulence factor regulator B (VfrB) as a potent regulator of α-hemolysin and other virulence factors in Staphylococcus aureus. In this study, we demonstrated that VfrB is a positive activator of the SaeRS two-component regulatory system. Analysis of vfrB, saeR, and saeS mutant strains revealed that VfrB functions in the same pathway as SaeRS. At the transcriptional level, the promoter activities of SaeRS class I (coa) and class II (hla) target genes were downregulated during the exponential growth phase in the vfrB mutant, compared to the wild-type strain. In addition, saePQRS expression was decreased in the vfrB mutant strain, demonstrating a need for this protein in the autoregulation of SaeRS. The requirement for VfrB-mediated activation was circumvented when SaeS was constitutively active due to an SaeS (L18P) substitution. Furthermore, activation of SaeS via human neutrophil peptide 1 (HNP-1) overcame the dependence on VfrB for transcription from class I Sae promoters. Consistent with the role of VfrB in fatty acid metabolism, hla expression was decreased in the vfrB mutant with the addition of exogenous myristic acid. Lastly, we determined that aspartic acid residues D38 and D40, which are predicted to be key to VfrB enzymatic activity, were required for VfrB-mediated α-hemolysin production. Collectively, this study implicates VfrB as a novel accessory protein needed for the activation of SaeRS in S. aureus. IMPORTANCE The SaeRS two-component system is a key regulator of virulence determinant production in Staphylococcus aureus. Although the regulon of this two-component system is well characterized, the activation mechanisms, including the specific signaling molecules, remain elusive. Elucidating the complex regulatory circuit of SaeRS regulation is important for understanding how the system contributes to disease causation by this pathogen. To this end, we have identified the fatty acid kinase VfrB as a positive regulatory modulator of SaeRS-mediated transcription of virulence factors in S. aureus. In addition to describing a new regulatory aspect of SaeRS, this study establishes a link between fatty acid kinase activity and virulence factor regulation.

scholarly journals Characterization of the Candida albicans Amino Acid Permease Family: Gap2 Is the Only General Amino Acid Permease and Gap4 Is an S-Adenosylmethionine (SAM) Transporter Required for SAM-Induced Morphogenesis

mSphere ◽  
2016 ◽  
Vol 1 (6) ◽  
Author(s):  
Lucie Kraidlova ◽  
Sanne Schrevens ◽  
Hélène Tournu ◽  
Griet Van Zeebroeck ◽  
Hana Sychrova ◽  
...  
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Amino Acids ◽  
Candida Albicans ◽  
Amino Acid ◽  
Virulence Factor ◽  
Amino Acid Transporters ◽  
Amino Acid Permease ◽  
Content Type ◽  
Important Virulence Factor ◽  
General Amino Acid Permease

ABSTRACT Candida albicans is a commensal organism that can thrive in many niches in its human host. The environmental conditions at these different niches differ quite a bit, and this fungus must be able to sense these changes and adapt its metabolism to them. Apart from glucose and other sugars, the uptake of amino acids is very important. This is underscored by the fact that the C. albicans genome encodes 6 orthologues of the Saccharomyces. cerevisiae general amino acid permease Gap1 and many other amino acid transporters. In this work, we characterize these six permeases and we show that C. albicans Gap2 is the functional orthologue of ScGap1 and that C. albicans Gap4 is an orthologue of ScSam3, an S-adenosylmethionine (SAM) transporter. Furthermore, we show that Gap4 is required for SAM-induced morphogenesis, an important virulence factor of C. albicans. Amino acids are key sources of nitrogen for growth of Candida albicans. In order to detect and take up these amino acids from a broad range of different and changing nitrogen sources inside the host, this fungus must be able to adapt via its expression of genes for amino acid uptake and further metabolism. We analyzed six C. albicans putative general amino acid permeases based on their homology to the Saccharomyces cerevisiae Gap1 general amino acid permease. We generated single- and multiple-deletion strains and found that, based on growth assays and transcriptional or posttranscriptional regulation, Gap2 is the functional orthologue to ScGap1, with broad substrate specificity. Expression analysis showed that expression of all GAP genes is under control of the Csy1 amino acid sensor, which is different from the situation in S. cerevisiae, where the expression of ScGAP1 is not regulated by Ssy1. We show that Gap4 is the functional orthologue of ScSam3, the only S-adenosylmethionine (SAM) transporter in S. cerevisiae, and we report that Gap4 is required for SAM-induced morphogenesis. IMPORTANCE Candida albicans is a commensal organism that can thrive in many niches in its human host. The environmental conditions at these different niches differ quite a bit, and this fungus must be able to sense these changes and adapt its metabolism to them. Apart from glucose and other sugars, the uptake of amino acids is very important. This is underscored by the fact that the C. albicans genome encodes 6 orthologues of the Saccharomyces. cerevisiae general amino acid permease Gap1 and many other amino acid transporters. In this work, we characterize these six permeases and we show that C. albicans Gap2 is the functional orthologue of ScGap1 and that C. albicans Gap4 is an orthologue of ScSam3, an S-adenosylmethionine (SAM) transporter. Furthermore, we show that Gap4 is required for SAM-induced morphogenesis, an important virulence factor of C. albicans.

scholarly journals Host Response Signature to Staphylococcus aureus Alpha-Hemolysin Implicates Pulmonary Th17 Response

2012 ◽  
Vol 80 (9) ◽  
pp. 3161-3169 ◽  
Author(s):  
Karen M. Frank ◽  
Tong Zhou ◽  
Liliana Moreno-Vinasco ◽  
Brian Hollett ◽  
Joe G. N. Garcia ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Virulence Factor ◽  
Expression Profiling ◽  
Host Response ◽  
Cellular Interactions ◽  
Wild Type ◽  
Th17 Response ◽  
Content Type ◽  
Alpha Hemolysin ◽  
Interleukin 23

ABSTRACTStaphylococcus aureuspneumonia causes significant morbidity and mortality. Alpha-hemolysin (Hla), a pore-forming cytotoxin ofS. aureus, has been identified through animal models of pneumonia as a critical virulence factor that induces lung injury. In spite of considerable molecular knowledge of how this cytotoxin injures the host, the precise host response to Hla in the context of infection remains poorly understood. We employed whole-genome expression profiling of infected lungs to define the host response to wild-typeS. aureuscompared with the response to an Hla-deficient isogenic mutant in experimental pneumonia. These data provide a complete expression profile at 4 and at 24 h postinfection, revealing a unique response to the toxin-expressing strain. Gene ontogeny analysis revealed significant differences in the extracellular matrix and cardiomyopathy pathways, both of which govern cellular interactions in the tissue microenvironment. Evaluation of individual transcript responses to Hla-secreting staphylococci was notable for upregulation of host cytokine and chemokine genes, including the p19 subunit of interleukin-23. Consistent with this observation, the cellular immune response to infection was characterized by a prominent Th17 response to the wild-type pathogen. These findings define specific host mRNA responses to Hla-producingS. aureus, coupling the pulmonary Th17 response to the secretion of this cytotoxin. Expression profiling to define the host response to a single virulence factor proved to be a valuable tool in identifying pathways for further investigation inS. aureuspneumonia. This approach may be broadly applicable to the study of bacterial toxins, defining host pathways that can be targeted to mitigate toxin-induced disease.

scholarly journals Host Fatty Acid Utilization by Staphylococcus aureus at the Infection Site

mBio ◽  
2020 ◽  
Vol 11 (3) ◽  
Author(s):  
Matthew W. Frank ◽  
Jiangwei Yao ◽  
Justin L. Batte ◽  
Jessica M. Gullett ◽  
Chitra Subramanian ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Fatty Acid ◽  
Molecular Species ◽  
De Novo ◽  
New Drugs ◽  
Pentadecanoic Acid ◽  
Infection Site ◽  
Wild Type ◽  
Content Type ◽  
Branched Chain

ABSTRACT Staphylococcus aureus utilizes the fatty acid (FA) kinase system to activate exogenous FAs for membrane synthesis. We developed a lipidomics workflow to determine the membrane phosphatidylglycerol (PG) molecular species synthesized by S. aureus at the thigh infection site. Wild-type S. aureus utilizes both host palmitate and oleate to acylate the 1 position of PG, and the 2 position is occupied by pentadecanoic acid arising from de novo biosynthesis. Inactivation of FakB2 eliminates the ability to assimilate oleate and inactivation of FakB1 reduces the content of saturated FAs and enhances oleate utilization. Elimination of FA activation in either ΔfakA or ΔfakB1 ΔfakB2 mutants does not impact growth. All S. aureus strains recovered from the thigh have significantly reduced branched-chain FAs and increased even-chain FAs compared to that with growth in rich laboratory medium. The molecular species pattern observed in the thigh was reproduced in the laboratory by growth in isoleucine-deficient medium containing exogenous FAs. S. aureus utilizes specific host FAs for membrane biosynthesis but also requires de novo FA biosynthesis initiated by isoleucine (or leucine) to produce pentadecanoic acid. IMPORTANCE The shortage of antibiotics against drug-resistant Staphylococcus aureus has led to the development of new drugs targeting the elongation cycle of fatty acid (FA) synthesis that are progressing toward the clinic. An objection to the use of FA synthesis inhibitors is that S. aureus can utilize exogenous FAs to construct its membrane, suggesting that the bacterium would bypass these therapeutics by utilizing host FAs instead. We developed a mass spectrometry workflow to determine the composition of the S. aureus membrane at the infection site to directly address how S. aureus uses host FAs. S. aureus strains that cannot acquire host FAs are as effective in establishing an infection as the wild type, but strains that require the utilization of host FAs for growth were attenuated in the mouse thigh infection model. We find that S. aureus does utilize host FAs to construct its membrane, but host FAs do not replace the requirement for pentadecanoic acid, a branched-chain FA derived from isoleucine (or leucine) that predominantly occupies the 2 position of S. aureus phospholipids. The membrane phospholipid structure of S. aureus mutants that cannot utilize host FAs indicates the isoleucine is a scarce resource at the infection site. This reliance on the de novo synthesis of predominantly pentadecanoic acid that cannot be obtained from the host is one reason why drugs that target fatty acid synthesis are effective in treating S. aureus infections.

scholarly journals Exogenous Fatty Acids Remodel Staphylococcus aureus Lipid Composition through Fatty Acid Kinase

2020 ◽  
Vol 202 (14) ◽  
Author(s):  
Zachary DeMars ◽  
Vineet K. Singh ◽  
Jeffrey L. Bose
Keyword(s):  
Fatty Acids ◽  
Staphylococcus Aureus ◽  
Oleic Acid ◽  
Fatty Acid ◽  
Lipid Composition ◽  
Unsaturated Fatty Acids ◽  
Mouse Skin ◽  
Membrane Composition ◽  
Wild Type ◽  
Content Type

ABSTRACT Staphylococcus aureus can utilize exogenous fatty acids for phospholipid synthesis. The fatty acid kinase FakA is essential for this utilization by phosphorylating exogenous fatty acids for incorporation into lipids. How FakA impacts the lipid membrane composition is unknown. In this study, we used mass spectrometry to determine the membrane lipid composition and properties of S. aureus in the absence of fakA. We found the fakA mutant to have increased abundance of lipids containing longer acyl chains. Since S. aureus does not synthesize unsaturated fatty acids, we utilized oleic acid (18:1) to track exogenous fatty acid incorporation into lipids. We observed a concentration-dependent incorporation of exogenous fatty acids into the membrane that required FakA. We also tested how FakA and exogenous fatty acids impact membrane-related physiology and identified changes in membrane potential, cellular respiration, and membrane fluidity. To mimic the host environment, we characterized the lipid composition of wild-type and fakA mutant bacteria grown in mouse skin homogenate. We show that wild-type S. aureus can incorporate exogenous unsaturated fatty acids from host tissue, highlighting the importance of FakA in the presence of host skin tissue. In conclusion, FakA is important for maintaining the composition and properties of the phospholipid membrane in the presence of exogenous fatty acids, impacting overall cell physiology. IMPORTANCE Environmental fatty acids can be harvested to supplement endogenous fatty acid synthesis to produce membranes and circumvent fatty acid biosynthesis inhibitors. However, how the inability to use these fatty acids impacts lipids is unclear. Our results reveal lipid composition changes in response to fatty acid addition and when S. aureus is unable to activate fatty acids through FakA. We identify concentration-dependent utilization of oleic acid that, when combined with previous work, provides evidence that fatty acids can serve as a signal to S. aureus. Furthermore, using mouse skin homogenates as a surrogate for in vivo conditions, we showed that S. aureus can incorporate host fatty acids. This study highlights how exogenous fatty acids impact bacterial membrane composition and function.

scholarly journals Staphylococcus aureus Tet38 Efflux Pump Structural Modeling and Roles of Essential Residues in Drug Efflux and Host Cell Internalization

2021 ◽  
Vol 89 (5) ◽  
Author(s):  
Q. C. Truong-Bolduc ◽  
Y. Wang ◽  
D. C. Hooper
Keyword(s):  
Amino Acids ◽  
Staphylococcus Aureus ◽  
Amino Acid ◽  
Host Cell ◽  
Tetracycline Resistance ◽  
Drug Efflux ◽  
Amino Acid Deletion ◽  
Content Type ◽  
Cell Internalization ◽  
External Loop

ABSTRACT The Staphylococcus aureus Tet38 membrane protein has distinct functions, including drug efflux and host cell attachment and internalization mediated by interaction with host cell CD36. Using structural modeling and site-directed mutagenesis, we identified key amino acids involved in different functions. Tet38, a member of the major facilitator superfamily, is predicted to have 14 transmembrane segments (TMS), 6 cytoplasmic loops, and 7 external loops. Cysteine substitutions of arginine 106 situated at the junction of TMS 4 and external loop L2, and glycine 151 of motif C on TMS 5, resulted in complete or near-complete (8- to 16-fold) reductions in Tet38-mediated resistance to tetracycline, with minimal to no effect on A549 host cell internalization. In contrast, a three-amino-acid deletion, F411P412G413, in external loop L7 situated between TMS 13 and 14 led to a decrease of 4-fold in S. aureus internalization by A549 cells and a partial effect on tetracycline resistance (4-fold reduction). A three-amino-acid deletion, D38D39L40, in external loop L1 situated between TMS-1 and TMS-2, had a similar partial effect on tetracycline resistance but did not affect cell internalization. Using an Ni column retention assay, we showed further that the L7, but not the L1, deletion impaired binding to CD36. Thus, the L7 domain of Tet38 is key for interaction with CD36 and host cell internalization, and amino acids R106 and G151 (TMSs 4 and 5) are particularly important for tetracycline resistance without affecting internalization.

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