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Mott PD, Zea AH, Lewis J, Mirzalieva O, Aiyar AA. Serine deamination by human serine racemase synergizes with antibiotics to curtail the replication of Chlamydia trachomatis. J Biol Chem 2024; 300:107350. [PMID: 38718865 PMCID: PMC11140210 DOI: 10.1016/j.jbc.2024.107350] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 04/28/2024] [Accepted: 04/30/2024] [Indexed: 05/28/2024] Open
Abstract
The obligate intracellular bacterium, Chlamydia trachomatis, has evolved to depend on its human host for many metabolites, including most amino acids and three of the four nucleotides. Given this, it is not surprising that depletion of a single amino acid in the host cell growth medium blocks chlamydial replication. Paradoxically, supra-normal levels of some amino acids also block productive replication of Chlamydia. Here, we have determined how elevated serine levels, generated by exogenous supplementation, impede chlamydial inclusion development and reduce the generation of infectious progeny. Our findings reveal that human serine racemase, which is broadly expressed in multiple tissues, potentiates the anti-chlamydial effect of elevated serine concentrations. In addition to reversibly converting l-serine to d-serine, serine racemase also deaminates serine via β-elimination. We have determined that d-serine does not directly impact Chlamydia; rather, ammonia generated by serine deamination limits the productive chlamydial replication. Our findings imply that ammonia produced within host cells can traverse the chlamydial inclusion membrane. Further, this property of serine deaminase can be exploited to sensitize Chlamydia to concentrations of doxycycline that are otherwise not bactericidal. Because exogenously elevated levels of serine can be tolerated over extended periods, the broad expression pattern of serine racemase indicates it to be a host enzyme whose activity can be directed against multiple intracellular bacterial pathogens. From a therapeutic perspective, demonstrating host metabolism can be skewed to generate an anti-bacterial metabolite that synergizes with antibiotics, we believe our results provide a new approach to target intracellular pathogens.
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Affiliation(s)
- Patricia D Mott
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA.
| | - Arnold H Zea
- Department of Microbiology, Immunology, & Parasitology, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA
| | - Jamiya Lewis
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA
| | - Oygul Mirzalieva
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA
| | - Ashok A Aiyar
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA.
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2
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Miyamoto T, Fushinobu S, Saitoh Y, Sekine M, Katane M, Sakai-Kato K, Homma H. Novel tetrahydrofolate-dependent d-serine dehydratase activity of serine hydroxymethyltransferases. FEBS J 2024; 291:308-322. [PMID: 37700610 DOI: 10.1111/febs.16953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2023] [Revised: 08/12/2023] [Accepted: 09/06/2023] [Indexed: 09/14/2023]
Abstract
d-Serine plays vital physiological roles in the functional regulation of the mammalian brain, where it is produced from l-serine by serine racemase and degraded by d-amino acid oxidase. In the present study, we identified a new d-serine metabolizing activity of serine hydroxymethyltransferase (SHMT) in bacteria as well as mammals. SHMT is known to catalyze the conversion of l-serine and tetrahydrofolate (THF) to glycine and 5,10-methylenetetrahydrofolate, respectively. In addition, we found that human and Escherichia coli SHMTs have d-serine dehydratase activity, which degrades d-serine to pyruvate and ammonia. We characterized this enzymatic activity along with canonical SHMT activity. Intriguingly, SHMT required THF to catalyze d-serine dehydration and did not exhibit dehydratase activity toward l-serine. Furthermore, SHMT did not use d-serine as a substrate in the canonical hydroxymethyltransferase reaction. The d-serine dehydratase activities of two isozymes of human SHMT were inhibited in the presence of a high concentration of THF, whereas that of E. coli SHMT was increased. The pH and temperature profiles of d-serine dehydratase and serine hydroxymethyltransferase activities of these three SHMTs were partially distinct. The catalytic efficiency (kcat /Km ) of dehydratase activity was lower than that of hydroxymethyltransferase activity. Nevertheless, the d-serine dehydratase activity of SHMT was physiologically important because d-serine inhibited the growth of an SHMT deletion mutant of E. coli, ∆glyA, more than that of the wild-type strain. Collectively, these results suggest that SHMT is involved not only in l- but also in d-serine metabolism through the degradation of d-serine.
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Affiliation(s)
- Tetsuya Miyamoto
- Graduate School of Pharmaceutical Sciences, Kitasato University, Tokyo, Japan
| | - Shinya Fushinobu
- Department of Biotechnology, The University of Tokyo, Japan
- Collaborative Research Institute for Innovative Microbiology, The University of Tokyo, Japan
| | - Yasuaki Saitoh
- Graduate School of Pharmaceutical Sciences, Kitasato University, Tokyo, Japan
| | - Masae Sekine
- Graduate School of Pharmaceutical Sciences, Kitasato University, Tokyo, Japan
| | - Masumi Katane
- Graduate School of Pharmaceutical Sciences, Kitasato University, Tokyo, Japan
| | - Kumiko Sakai-Kato
- Graduate School of Pharmaceutical Sciences, Kitasato University, Tokyo, Japan
| | - Hiroshi Homma
- Graduate School of Pharmaceutical Sciences, Kitasato University, Tokyo, Japan
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Philip BM, John JS, George M, Kumar KM, M V, HS HK, Devarajegowda H, Kotresh O, Paulose TAP, Sajan D. Synthesis, comprehensive spectroscopic investigation and molecular docking studies of (6-Fluoro-2-oxo-2H-chromen-4-yl) methyl morpholine-4-carbodithioate. J Mol Struct 2022. [DOI: 10.1016/j.molstruc.2022.133694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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4
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Wang S, Ma Y, Li Y, Ge X, Lu C, Cai C, Yang Y, Zhao Y, Liang G, Guo X, Cao G, Li B, Gao P. Long non-coding RNAs in <i>Sus scrofa</i> ileum under starvation stress. Anim Biosci 2022; 35:975-988. [PMID: 35240026 PMCID: PMC9271390 DOI: 10.5713/ab.21.0483] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Accepted: 02/04/2022] [Indexed: 11/27/2022] Open
Abstract
Objective In this study, we aimed to identify long non-coding RNAs (lncRNAs) that play important roles in starvation stress, analyze their functions, and discover potential molecular targets to alleviate starvation stress to provide a theoretical reference for subsequent in-depth research. Methods We generated a piglet starvation stress animal model. Nine Yorkshire weaned piglets were randomly divided into a long-term starvation stress group (starved for 72 h), short-term starvation stress group (starved for 48 h), and the control group. LncRNA libraries were constructed using high-throughput sequencing of piglet ileums. Results We obtained 11,792 lncRNAs, among which, 2,500 lncRNAs were novel. In total, 509 differentially expressed (DE)lncRNAs were identified in this study. Target genes of DElncRNAs were predicted via cis and trans interactions, and functional and pathway analyses were performed. Gene ontology functions and Kyoto encyclopedia of genes and genomes analysis revealed that lncRNA-targeted genes mainly participated in metabolic pathways, cellular processes, immune system processes, digestive systems, and transport activities. To reveal the mechanism underlying starvation stress, the interaction network between lncRNAs and their targets was constructed based on 26 DElncRNAs and 72 DEmRNAs. We performed an interaction network analysis of 121 DElncRNA–DEmRNA pairs with a Pearson correlation coefficient greater than 0.99. Conclusion We found that MSTRG.19894.13, MSTRG.16726.3, and MSTRG.12176.1 might play important roles in starvation stress. This study not only generated a library of enriched lncRNAs in piglets, but its outcomes also provide a strong foundation to screen key lncRNAs involved in starvation stress and a reference for subsequent in-depth research.
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Potter JHT, Davies KTJ, Yohe LR, Sanchez MKR, Rengifo EM, Struebig M, Warren K, Tsagkogeorga G, Lim BK, dos Reis M, Dávalos LM, Rossiter SJ. Dietary Diversification and Specialization in Neotropical Bats Facilitated by Early Molecular Evolution. Mol Biol Evol 2021; 38:3864-3883. [PMID: 34426843 PMCID: PMC8382914 DOI: 10.1093/molbev/msab028] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Dietary adaptation is a major feature of phenotypic and ecological diversification, yet the genetic basis of dietary shifts is poorly understood. Among mammals, Neotropical leaf-nosed bats (family Phyllostomidae) show unmatched diversity in diet; from a putative insectivorous ancestor, phyllostomids have radiated to specialize on diverse food sources including blood, nectar, and fruit. To assess whether dietary diversification in this group was accompanied by molecular adaptations for changing metabolic demands, we sequenced 89 transcriptomes across 58 species and combined these with published data to compare ∼13,000 protein coding genes across 66 species. We tested for positive selection on focal lineages, including those inferred to have undergone dietary shifts. Unexpectedly, we found a broad signature of positive selection in the ancestral phyllostomid branch, spanning genes implicated in the metabolism of all major macronutrients, yet few positively selected genes at the inferred switch to plantivory. Branches corresponding to blood- and nectar-based diets showed selection in loci underpinning nitrogenous waste excretion and glycolysis, respectively. Intriguingly, patterns of selection in metabolism genes were mirrored by those in loci implicated in craniofacial remodeling, a trait previously linked to phyllostomid dietary specialization. Finally, we show that the null model of the widely-used branch-site test is likely to be misspecified, with the implication that the test is too conservative and probably under-reports true cases of positive selection. Our findings point to a complex picture of adaptive radiation, in which the evolution of new dietary specializations has been facilitated by early adaptations combined with the generation of new genetic variation.
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Affiliation(s)
- Joshua H T Potter
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Kalina T J Davies
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Laurel R Yohe
- Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY, USA
- Department of Earth and Planetary Science, Yale University, 210 Whitney Ave, New Haven, CT, USA
| | - Miluska K R Sanchez
- Escuela Profesional de Ciencias Biológicas, Universidad Nacional de Piura, Piura, Peru
| | - Edgardo M Rengifo
- Escola Superior de Agricultura ‘Luiz de Queiroz,’ Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Piracicaba, Brazil
- Centro de Investigación Biodiversidad Sostenible (BioS), Lima, Peru
| | - Monika Struebig
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Kim Warren
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Georgia Tsagkogeorga
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Burton K Lim
- Department of Natural History, Royal Ontario Museum, Toronto, ON, Canada
| | - Mario dos Reis
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
| | - Liliana M Dávalos
- Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY, USA
- Consortium for Inter-Disciplinary Environmental Research, Stony Brook University, Stony Brook, NY, USA
| | - Stephen J Rossiter
- School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom
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Identification of an l-serine/l-threonine dehydratase with glutamate racemase activity in mammals. Biochem J 2020; 477:4221-4241. [DOI: 10.1042/bcj20200721] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 10/12/2020] [Accepted: 10/20/2020] [Indexed: 02/02/2023]
Abstract
Recent investigations have shown that multiple d-amino acids are present in mammals and these compounds have distinctive physiological functions. Free d-glutamate is present in various mammalian tissues and cells and in particular, it is presumably correlated with cardiac function, and much interest is growing in its unique metabolic pathways. Recently, we first identified d-glutamate cyclase as its degradative enzyme in mammals, whereas its biosynthetic pathway in mammals is unclear. Glutamate racemase is a most probable candidate, which catalyzes interconversion between d-glutamate and l-glutamate. Here, we identified the cDNA encoding l-serine dehydratase-like (SDHL) as the first mammalian clone with glutamate racemase activity. This rat SDHL had been deposited in mammalian databases as a protein of unknown function and its amino acid sequence shares ∼60% identity with that of l-serine dehydratase. Rat SDHL was expressed in Escherichia coli, and the enzymatic properties of the recombinant were characterized. The results indicated that rat SDHL is a multifunctional enzyme with glutamate racemase activity in addition to l-serine/l-threonine dehydratase activity. This clone is hence abbreviated as STDHgr. Further experiments using cultured mammalian cells confirmed that d-glutamate was synthesized and l-serine and l-threonine were decomposed. It was also found that SDHL (STDHgr) contributes to the homeostasis of several other amino acids.
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Viola RE. The ammonia-lyases: enzymes that use a wide range of approaches to catalyze the same type of reaction. Crit Rev Biochem Mol Biol 2020; 54:467-483. [PMID: 31906712 DOI: 10.1080/10409238.2019.1708261] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The paradigm that protein structure determines protein function has been clearly established. What is less clear is whether a specific protein structure is always required to carry out a specific function. Numerous cases are now known where there is no apparent connection between the biological function of a protein and the other members of its structural class, and where functionally related proteins can have quite diverse structures. A set of enzymes with these diverse properties, the ammonia-lyases, will be examined in this review. These are a class of enzymes that catalyze a relatively straightforward deamination reaction. However, the individual enzymes of this class possess a wide variety of different structures, utilize a diverse set of cofactors, and appear to catalyze this related reaction through a range of different mechanisms. This review aims to address a basic question: if there is not a specific protein structure and active site architecture that is both required and sufficient to define a catalyst for a given chemical reaction, then what factor(s) determine the structure and the mechanism that is selected to catalyze a particular reaction?
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Affiliation(s)
- Ronald E Viola
- Department of Chemistry and Biochemistry, University of Toledo, Toledo, OH, USA
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Ernst DC, Downs DM. Mmf1p Couples Amino Acid Metabolism to Mitochondrial DNA Maintenance in Saccharomyces cerevisiae. mBio 2018; 9:e00084-18. [PMID: 29487232 PMCID: PMC5829821 DOI: 10.1128/mbio.00084-18] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Accepted: 01/18/2018] [Indexed: 12/11/2022] Open
Abstract
A variety of metabolic deficiencies and human diseases arise from the disruption of mitochondrial enzymes and/or loss of mitochondrial DNA. Mounting evidence shows that eukaryotes have conserved enzymes that prevent the accumulation of reactive metabolites that cause stress inside the mitochondrion. 2-Aminoacrylate is a reactive enamine generated by pyridoxal 5'-phosphate-dependent α,β-eliminases as an obligatory intermediate in the breakdown of serine. In prokaryotes, members of the broadly conserved RidA family (PF14588) prevent metabolic stress by deaminating 2-aminoacrylate to pyruvate. Here, we demonstrate that unmanaged 2-aminoacrylate accumulation in Saccharomyces cerevisiae mitochondria causes transient metabolic stress and the irreversible loss of mitochondrial DNA. The RidA family protein Mmf1p deaminates 2-aminoacrylate, preempting metabolic stress and loss of the mitochondrial genome. Disruption of the mitochondrial pyridoxal 5'-phosphate-dependent serine dehydratases (Ilv1p and Cha1p) prevents 2-aminoacrylate formation, avoiding stress in the absence of Mmf1p. Furthermore, chelation of iron in the growth medium improves maintenance of the mitochondrial genome in yeast challenged with 2-aminoacrylate, suggesting that 2-aminoacrylate-dependent loss of mitochondrial DNA is influenced by disruption of iron homeostasis. Taken together, the data indicate that Mmf1p indirectly contributes to mitochondrial DNA maintenance by preventing 2-aminoacrylate stress derived from mitochondrial amino acid metabolism.IMPORTANCE Deleterious reactive metabolites are produced as a consequence of many intracellular biochemical transformations. Importantly, reactive metabolites that appear short-lived in vitro have the potential to persist within intracellular environments, leading to pervasive cell damage and diminished fitness. To overcome metabolite damage, organisms utilize enzymatic reactive-metabolite defense systems to rid the cell of deleterious metabolites. In this report, we describe the importance of the RidA/YER057c/UK114 enamine/imine deaminase family in preventing 2-aminoacrylate stress in yeast. Saccharomyces cerevisiae lacking the enamine/imine deaminase Mmf1p was shown to experience pleiotropic growth defects and fails to maintain its mitochondrial genome. Our results provide the first line of evidence that uncontrolled 2-aminoacrylate stress derived from mitochondrial serine metabolism can negatively impact mitochondrial DNA maintenance in eukaryotes.
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Affiliation(s)
- Dustin C Ernst
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
| | - Diana M Downs
- Department of Microbiology, University of Georgia, Athens, Georgia, USA
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Qin Z, Yan Q, Ma Q, Jiang Z. Crystal structure and characterization of a novel L-serine ammonia-lyase from Rhizomucor miehei. Biochem Biophys Res Commun 2015; 466:431-7. [PMID: 26367174 DOI: 10.1016/j.bbrc.2015.09.043] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2015] [Accepted: 09/08/2015] [Indexed: 11/16/2022]
Abstract
L-serine ammonia-lyase, as a member of the β-family of pyridoxal-5'-phosphate (PLP) dependent enzymes, catalyzes the conversion of L-serine (L-threonine) to pyruvate (α-ketobutyrate) and ammonia. The crystal structure of L-serine ammonia-lyase from Rhizomucor miehei (RmSDH) was solved at 1.76 Å resolution by X-ray diffraction method. The overall structure of RmSDH had the characteristic β-family PLP dependent enzyme fold. It consisted of two distinct domains, both of which show the typical open twisted α/β structure. A PLP cofactor was located in the crevice between the two domains, which was attached to Lys52 by a Schiff-base linkage. Unique residue substitutions (Gly78, Pro79, Ser146, Ser147 and Thr312) were discovered at the catalytic site of RmSDH by comparison of structures of RmSDH and other reported eukaryotic L-serine ammonia-lyases. Optimal pH and temperature of the purified RmSDH were 7.5 and 40 °C, respectively. It was stable in the pH range of 7.0-9.0 and at temperatures below 40 °C. This is the first crystal structure of a fungal L-serine ammonia-lyase. It will be useful to study the catalytic mechanism of β-elimination enzymes and will provide a basis for further enzyme engineering.
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Affiliation(s)
- Zhen Qin
- College of Food Science and Nutritional Engineering, Beijing Advanced Innovation Center of Food Nutrition and Human Health, China Agricultural University, Beijing 100083, China
| | - Qiaojuan Yan
- College of Engineering, China Agricultural University, Beijing 100083, China
| | - Qingjun Ma
- Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
| | - Zhengqiang Jiang
- College of Food Science and Nutritional Engineering, Beijing Advanced Innovation Center of Food Nutrition and Human Health, China Agricultural University, Beijing 100083, China.
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Montefusco DJ, Newcomb B, Gandy JL, Brice SE, Matmati N, Cowart LA, Hannun YA. Sphingoid bases and the serine catabolic enzyme CHA1 define a novel feedforward/feedback mechanism in the response to serine availability. J Biol Chem 2012; 287:9280-9. [PMID: 22277656 DOI: 10.1074/jbc.m111.313445] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Targets of bioactive sphingolipids in Saccharomyces cerevisiae were previously identified using microarray experiments focused on sphingolipid-dependent responses to heat stress. One of these heat-induced genes is the serine deamidase/dehydratase Cha1 known to be regulated by increased serine availability. This study investigated the hypothesis that sphingolipids may mediate the induction of Cha1 in response to serine availability. The results showed that inhibition of de novo synthesis of sphingolipids, pharmacologically or genetically, prevented the induction of Cha1 in response to increased serine availability. Additional studies implicated the sphingoid bases phytosphingosine and dihydrosphingosine as the likely mediators of Cha1 up-regulation. The yeast protein kinases Pkh1 and Pkh2, known sphingoid base effectors, were found to mediate CHA1 up-regulation via the transcription factor Cha4. Because the results disclosed a role for sphingolipids in negative feedback regulation of serine metabolism, we investigated the effects of disrupting this mechanism on sphingolipid levels and on cell growth. Intriguingly, exposure of the cha1Δ strain to high serine resulted in hyperaccumulation of endogenous serine and in turn a significant accumulation of sphingoid bases and ceramides. Under these conditions, the cha1Δ strain displayed a significant growth defect that was sphingolipid-dependent. Together, this work reveals a feedforward/feedback loop whereby the sphingoid bases serve as sensors of serine availability and mediate up-regulation of Cha1 in response to serine availability, which in turn regulates sphingolipid levels by limiting serine accumulation.
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Affiliation(s)
- David J Montefusco
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina 29403, USA
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Goto M, Yamauchi T, Kamiya N, Miyahara I, Yoshimura T, Mihara H, Kurihara T, Hirotsu K, Esaki N. Crystal structure of a homolog of mammalian serine racemase from Schizosaccharomyces pombe. J Biol Chem 2009; 284:25944-52. [PMID: 19640845 DOI: 10.1074/jbc.m109.010470] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
D-serine is an endogenous coagonist for the N-methyl-D-aspartate receptor and is involved in excitatory neurotransmission in the brain. Mammalian pyridoxal 5'-phosphate-dependent serine racemase, which is localized in the mammalian brain, catalyzes the racemization of L-serine to yield D-serine and vice versa. The enzyme also catalyzes the dehydration of D- and L-serine. Both reactions are enhanced by Mg.ATP in vivo. We have determined the structures of the following three forms of the mammalian enzyme homolog from Schizosaccharomyces pombe: the wild-type enzyme, the wild-type enzyme in the complex with an ATP analog, and the modified enzyme in the complex with serine at 1.7, 1.9, and 2.2 A resolution, respectively. On binding of the substrate, the small domain rotates toward the large domain to close the active site. The ATP binding site was identified at the domain and the subunit interface. Computer graphics models of the wild-type enzyme complexed with L-serine and D-serine provided an insight into the catalytic mechanisms of both reactions. Lys-57 and Ser-82 located on the protein and solvent sides, respectively, with respect to the cofactor plane, are acid-base catalysts that shuttle protons to the substrate. The modified enzyme, which has a unique "lysino-D-alanyl" residue at the active site, also exhibits catalytic activities. The crystal-soaking experiment showed that the substrate serine was actually trapped in the active site of the modified enzyme, suggesting that the lysino-D-alanyl residue acts as a catalytic base in the same manner as inherent Lys-57 of the wild-type enzyme.
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Affiliation(s)
- Masaru Goto
- Department of Chemistry, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan
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