Role Of Methionine Research Articles

NMR characterization of a Cu(i)-bound peptide model of copper metallochaperones: Insights on the role of methionine

The first NMR structure of a Cu(I)-bound metallochaperone model with the conserved sequence MT/HCXXC revealed that at pH ∼3.0 and ∼6.8 Cu(I) binds through one Cys and the Met rather than the two Cys residues, differently than at pH ∼8.5. This suggests a possible role of Met in metal transport.

The Role of Methionine Oxidation/Reduction in the Regulation of Immune Response

Methionine oxidation by reactive oxygen species and reduction mediated by the methionine sulfoxide reductase (Msr) system may attenuate protein function in signal transduction pathways. This review will focus on two potential protein targets for methionine oxidation involved in signal transduction of the immune response: Ca(2+)/calmodulin-regulated phosphatase calcineurin (Cn) and inhibitor of kappa B-alpha (IkBα). The major known function of Cn is to regulate nuclear localization of the nuclear factor of activated T cells (NFAT), a family of transcription factors during immune stimulus. Like wise, IκBα inhibits the activity of nuclear factor kappa B (NFkB), which is known to regulate the transcription of various genes participating in immunological and oxidative stress response. Modification of Met (45) in IκBα enhances its resistance to protein-degredation; thereby, preventing NFkB from activating transcription in cells of the immune system. Similarly, the human Cn molecule contains several methionine residues that are either located next to a cysteine residue or a methionine residue. Accordingly, it is suggested that oxidation of a specific Cn-methionine may interfere with the proper NFAT nuclear-localization and transcriptional activation in T-cell. Thus, the roles of oxidized-methionine residues and their reduction, by the Msr system, are discussed as potential regulators of cellular immune response.

Toxicity of Methionine in Humans

The literature has been searched to identify evidence relating to the possible toxicity of the amino acid methionine in human subjects. Nutritional and metabolic studies have employed amounts of methionine, including the d and dl isomers, both below and above the requirement and have not reported adverse effects in adults and children. Although methionine is known to exacerbate psychopathological symptoms in schizophrenic patients, there is no evidence of similar effects in healthy subjects. The role of methionine as a precursor of homocysteine is the most notable cause for concern. A "loading dose" of methionine (0.1 g/kg) has been given, and the resultant acute increase in plasma homocysteine has been used as an index of the susceptibility to cardiovascular disease. Although this procedure results in vascular dysfunction, this is acute and unlikely to result in permanent damage. However, a 10-fold larger dose, given mistakenly, resulted in death. Longer-term studies in adults have indicated no adverse consequences of moderate fluctuations in dietary methionine intake, but intakes higher than 5 times normal resulted in elevated homocysteine levels. These effects of methionine on homocysteine and vascular function are moderated by supplements of vitamins B-6, B-12, C, and folic acid. In infants, methionine intakes of 2-5 times normal resulted in impaired growth and extremely high plasma methionine levels, but no adverse long-term consequences were observed.

Carbon source induced yeast-to-hypha transition in Candida albicans is dependent on the presence of amino acids and on the G-protein-coupled receptor Gpr1

Yeast-to-hypha transition in Candida albicans can be induced by a wide variety of factors, including specific nutrients. We have started to investigate the mechanism by which some of these nutrients may be sensed. The G-protein-coupled receptor Gpr1 is required for yeast-to-hypha transition on various solid hypha-inducing media. Recently we have shown induction of Gpr1 internalization by specific amino acids, e.g. methionine. This suggests a possible role for methionine as a ligand of CaGpr1. Here we show that there is a big variation in methionine-induced hypha formation depending on the type of carbon source present in the medium. In addition high glucose concentrations repress hypha formation whereas a concentration of 0.1%, which mimics the glucose concentration present in the bloodstream, results in maximal hypha formation. Hence, it remains unclear whether Gpr1 senses sugars, as in Saccharomyces cerevisiae, or specific amino acids like methionine.

Role of methionine in nocturnal melatonin peak in the pineal gland.

Methionine dose-dependently stimulated O-methylation of hydroxyindoles in the pineal gland and contributed to the nocturnal melatonin peak in adult male Wistar rats. Methionine is involved in the maintenance of diurnal rhythms by regulating biochemical transformations of indoles in pinealocytes. Our findings provide theoretical basis for new applications of methionine.

Selective nitration of Tyr99 in calmodulin as a marker of cellular conditions of oxidative stress.

We examined the possible role of methionines as oxidant scavengers that prevent the peroxynitrite-induced nitration of tyrosines within calmodulin (CaM). We used mass spectrometry to investigate the reactivity of peroxynitrite with CaM at physiological pH. The possible role of methionines in scavenging peroxynitrite (ONOO-) was assessed in wild-type CaM and following substitution of all nine methionines in CaM with leucines. We find that peroxynitrite selectively nitrates Tyr99 at physiological pH, resulting in the formation of between 0.05 and 0.25 mol of nitrotyrosine/mol of CaM when the added molar ratio of peroxynitrite per CaM was varied between 2.5 and 1.5. In wild-type CaM there is a corresponding oxidation of between 0.8 and 2.8 mol of methionine to form methionine sulfoxide. However, following site-directed substitution of all nine methionines in wild-type CaM with leucines, the extent of nitration by peroxynitrite was unchanged. These results indicate that Tyr99 is readily nitrated by peroxynitrite and that methionine side chains do not function as an antioxidant in scavenging peroxynitrite. Thus, separate reactive species are involved in the oxidation of methionine and nitration of Tyr99 whose relative concentrations are determined by solution conditions. The sensitivity of Tyr99 in CaM to nitration suggests that CaM-dependent signaling pathways are sensitive to peroxynitrite formation and that nitration of CaM represents a cellular marker of peroxynitrite-induced changes in cellular function.

Independent roles of methionine and O-acetyl-l-serine in the regulation of the β subunit gene of β-conglycinin

The gene encoding the β subunit of β-conglycinin, one of the major seed storage proteins of soybean (Glycine max [L.] Merr.) , is downregulated by methionine (Met) and upregulated by O-acetyl-l-serine (OAS). We examined the interaction between Met and OAS in the regulation of the expression of the β subunit gene in in vitro-cultured immature soybean cotyledons. Application of Met reduced the accumulation of the β subunit both in the presence and absence of OAS in the media: Application of OAS increased the accumulation of the β subunit both in the presence and absence of Met. We also studied the regulation of the β subunit gene promoter by sulfur in Arabidopsis thaliana (L.) Heynh. mutant mto1-1, that over-accumulates soluble Met, using the β-glucuronidase (GUS) gene as a reporter. When grown under sulfur-deficient conditions, the GUS activity in seeds of the transgenic plants carrying the mto1-1 mutation was lower than that of the plants which do not carry the mutation, suggesting that the β subunit gene promoter was downregulated by the mto1-1 mutation under sulfur deficiency. When the transgenic plants carrying the mto1-1 mutation were grown under control and sulfur-deficient conditions, the GUS activity was higher under sulfur-deficient conditions, suggesting that the β subunit gene promoter was upregulated by sulfur deficiency even in the mto1-1 mutant background. Furthermore, OAS contents in immature siliques were elevated both in the mto1-1 mutant and wild-type plants under sulfur deficiency. Met contents in immature siliques of the mto1-1 mutant plants increased even under sulfur deficiency. There was a strong positive correlation between the GUS activities in seeds and the endogenous [OAS]/[Met] ratio. These results suggest that OAS and Met regulate the β subunit accumulation through independent pathways.

3D0930 PYPにおけるメチオニン100の役割(18.光生物(A)視覚,一般講演,日本生物物理学会第40回年会)

3D0930 PYPにおけるメチオニン100の役割(18.光生物(A)視覚,一般講演,日本生物物理学会第40回年会)

Is Oxidative Damage by β-Amyloid and Prion Peptides Mediated by Hydrogen Atom Transfer from Glycine α-Carbon to Methionine Sulfur within β-Sheets?

Methionine in glycine-rich regions of both β-amyloid peptide and prion peptide is thought to be crucial to their neurotoxic properties. We postulate here a role for methionine in the propagation of oxidative damage. The S−H bond dissociation enthalpies, BDE(S−H)s, of dimethylsulfonium ion (CH3)2SH+ and a S-protonated methionine residue of a polypeptide strand are estimated to be 351 and 326−331 kJ mol-1, respectively, by the application of calculations at the B3LYP level with large basis sets. These species are direct products of H atom abstraction by radical cations of sulfides. The reactions between a glycine residue and the radical cations of (CH3)2S and Met were investigated and the transition structures for H atom transfer located. The results suggest that it is thermodynamically feasible for the S-ionized form of Met to cause oxidative damage at the αC−H site of almost any amino acid residue of a nearby polypeptide strand (BDE(αC−H) = 330−360 kJ mol-1) or to nearby lipids with a bis(allylic) methylene group (BDE(C−H) = 335 kJ mol-1). However, a key observation is that, when the Met residue is incorporated into an antiparallel β-sheet, only a Gly residue is exposed and susceptible to oxidation at the αC−H site. Furthermore, the Gly must lie on a strand of the β-sheet different from that containing Met and must be part of a (5,5) rather than a (3,3) cycle. The same considerations apply to the methyl-deprotonated form of the sulfide radical cation but not the methylene-deprotonated form. These findings suggest a possible mechanism for generating and propagating oxidative damage via a Met residue of the Aβ peptide of Alzheimer's disease and of the prion peptide of Creutzfeldt−Jakob disease. To our knowledge, this is the first proposed mechanism that accounts for the radical damage in either of these diseases and requires peptide β-sheets and amino acids, methionine and glycine.

Incorporation of 14C into methionine as an intermediate for phytosiderophore biosynthesis in barley

In order to verify the precursory role of methionine (Met) in the biosynthesis of the mugineic acid family of phytosiderophores (MAs), feeding experiments of 14C-Iabeled compounds to barley (Hordeum vulgare L. cv. Minorimugi) roots grown hydroponically were conducted. When both l4C-Glucose (Glc) and unlabeled Met were fed to segmented roots, 14C was incorporated into Met and MAs in the roots. Molar-radioactivity of Met was higher than that of the amino-butanoic-acid unit in MAs in the roots. When l4C-Glc and unlabeled homoserine (Hse) were fed to decapitated roots, l4C was incorporated into Met but not into Hse. Therefore, it was considered that Hse might not be a major precursor of MAs. In addition, 14C was incorporated into Met and MAs in the roots when both 14C-glycerol (Gol) and unlabeled Met were fed to segmented roots. It is suggested that MAs may be synthesized from Glc via Met, bypassing Hse, and that the MAs biosynthesis may involve an unknown pathway associated with Gol and leading to Met.

Role of methionine as a methyl group donor in cattle (1999)

Holstein steers were used in two 5 × 5 Latin square experiments to evaluate the sparing of methionine by alternative sources of methyl groups (betaine or choline). Steers were housed in metabolism crates and limit fed a diet high in rumen degradable protein. To increase energy supply, volatile fatty acids were infused into the rumens, and glucose was infused into the abomasum. An amino acid mixture, limiting in methionine, was infused abomasally to ensure that non-sulfur amino acids did not limit protein synthesis. Treatments for Exp. 1 were abomasal infusion of 1) water (control), 2) 2 g/day additional L-methionine, 3) 1.7 g/day Lcysteine, 4) 1.6 g/day betaine, and 5) 1.7 g/day L-cysteine + 1.6 g/day betaine. Treatments for Exp. 2 were abomasal infusion of 1) water (control), 2) 2 g/day additional L-methionine, 3) 8 g/day betaine, 4) 16 g/day betaine, and 5) 8 g/day choline. In both experiments, nitrogen retention increased (P<.05) in response to methionine, demonstrating a deficiency of sulfur amino acids. Responses to cysteine, betaine and choline were small. The low response to cysteine indicates that either the response to methionine is not due to transsulfuration to cysteine, or that cysteine supply does not alter the flux of methionine through transsulfuration. The small responses to betaine and choline suggest that they do not substitute for methionine. Thus, under our experimental conditions, responses to methionine likely were due to a correction of a deficiency of methionine per se rather than of methyl group donors.

Mechanisms of Nutritionally Caused Congenital Malformations: The Role of Methionine in Counteracting Antiserum-Induced Embryopathy • 362

Mechanisms of Nutritionally Caused Congenital Malformations: The Role of Methionine in Counteracting Antiserum-Induced Embryopathy • 362

Lithium toxicity in yeast is due to the inhibition of RNA processing enzymes.

Hal2p is an enzyme that converts pAp (adenosine 3',5' bisphosphate), a product of sulfate assimilation, into 5' AMP and Pi. Overexpression of Hal2p confers lithium resistance in yeast, and its activity is inhibited by submillimolar amounts of Li+ in vitro. Here we report that pAp accumulation in HAL2 mutants inhibits the 5'-->3' exoribonucleases Xrn1p and Rat1p. Li+ treatment of a wild-type yeast strain also inhibits the exonucleases, as a result of pAp accumulation due to inhibition of Hal2p; 5' processing of the 5.8S rRNA and snoRNAs, degradation of pre-rRNA spacer fragments and mRNA turnover are inhibited. Lithium also inhibits the activity of RNase MRP by a mechanism which is not mediated by pAp. A mutation in the RNase MRP RNA confers Li+ hypersensitivity and is synthetically lethal with mutations in either HAL2 or XRN1. We propose that Li+ toxicity in yeast is due to synthetic lethality evoked between Xrn1p and RNase MRP. Similar mechanisms may contribute to the effects of Li+ on development and in human neurobiology.

The role of methionine and cystine in the growth and viability of secondary hair follicles of the Cashmere goat in vitro

A supply of sulphur-containing amino acids is essential for the growth of hair fibre in animals.The main sulphur-containing amino acid quantitatively required for the synthesis of fibre protein is cystine or its monomeric form cysteine,which may be absorbed from the digestive tract or converted from methionine via the transulphuration pathway.The predominant sites of the transulphuration pathway in ruminants are the liver (Radcliffe and Egan,1978)and the heterogenous system in the skin (Downes et al,1964).The aims of the study were to determine the importance of the supply of cystine and methionine for the growth and viability of the cashmere secondary hair follicle in vitro and to investigate whether cystine could successfully be replaced by methionine in this homogenous system.

The role of methionine and cystine in the growth and viability of secondary hair follicles of the Cashmere goat in vitro

A supply of sulphur-containing amino acids is essential for the growth of hair fibre in animals.The main sulphur-containing amino acid quantitatively required for the synthesis of fibre protein is cystine or its monomeric form cysteine,which may be absorbed from the digestive tract or converted from methionine via the transulphuration pathway.The predominant sites of the transulphuration pathway in ruminants are the liver (Radcliffe and Egan,1978)and the heterogenous system in the skin (Downes et al,1964).The aims of the study were to determine the importance of the supply of cystine and methionine for the growth and viability of the cashmere secondary hair follicle in vitro and to investigate whether cystine could successfully be replaced by methionine in this homogenous system.

Role of methionine in the active site of alpha-galactosidase from Trichoderma reesei.

alpha-Galactosidase from Trichoderma reesei when treated with H2O2 shows a 12-fold increase in activity towards p-nitrophenyl alpha-D-galactopyranoside. A similar effect is produced by the treatment of alpha-galactosidase with other non-specific oxidants: NaIO4, KMnO4 and K4S4O8. In addition to the increase in activity, the Michaelis constant rises from 0.2 to 1.4 mM, the temperature coefficient decreases by a factor of 1.5 and the pH-activity curve falls off sharply with increasing pH. Galactose (a competitive inhibitor of alpha-galactosidase; Ki 0.09 mM for the native enzyme at pH 4.4) effectively inhibits oxidative activation of the enzyme, because the observed activity changes are related to oxidation of the catalytically important methionine in the active site. NMR measurements and amino acid analysis show that oxidation to methionine sulphoxide of one of five methionines is sufficient to activate alpha-galactosidase. Binding of galactose prevents this. Oxidative activation does not lead to conversion of other H2O2-sensitive amino acid residues, such as histidine, tyrosine, tryptophan and cysteine. The catalytically important cysteine thiol group is quantitatively titrated after protein oxidative activation. Further oxidation of methionines (up to four of five residues) can be achieved by increasing the oxidation time and/or by prior denaturation of the protein. Obviously, a methionine located in the active site of alpha-galactosidase is more accessible. The oxidative-activation phenomenon can be explained by a conformational change in the active site as a result of conversion of non-polar methionine into polar methionine sulphoxide.

Purification and characterization of alpha 1-antichymotrypsin-like protease inhibitor that regulates prohormone thiol protease involved in enkephalin precursor processing.

Evidence is presented showing that alpha 1-antichymotrypsin (ACT) inhibits a novel prohormone thiol protease (PTP) involved in processing the enkephalin precursor. Colocalization of ACT immunoreactivity with PTP within isolated secretory vesicles of bovine adrenal medulla and pituitary indicated that endogenous ACT could regulate PTP in vivo. The endogenous 60 kDa bovine ACT (bACT)-like protein was purified from pituitary by chromatography on DEAE-Sepharose, chromatofocusing, butyl-Sepharose, and Sephacryl S-200. Characterization showed that the bACT-like protein was a potent inhibitor of PTP (Ki,app value of 2.2 nM) as well as an effective inhibitor of chymotrypsin (Ki,app value of 2.3 nM). Furthermore, the bACT-like protein formed sodium dodecyl sulfate-stable complexes with chymotrypsin, which is typical of serpin protease inhibitors. Importantly, PTP formed sodium dodecyl sulfate-stable complexes with human ACT, suggesting that PTP's cleavage specificity may resemble the reactive center of ACT. PTP cleavage of enkephalin-containing peptides at the NH2-terminal side of paired basic residues (Lys-Arg, Arg-Arg, Lys-Lys), flanking the COOH terminus of (Met)enkephalin (Tyr-Gly-GLy-Phe-Met), indicates methionine at the P1 position. PTP cleavage of peptide-methylcoumarin amide and peptide-p-nitroanilide substrates demonstrated specificity for paired basic and monobasic residues, as well as a role for methionine in PTP's cleavage site. These results showing PTP's ability for processing at a methionine residue which resembles the P1 specificity of ACT are compatible with inhibition of PTP by ACT. These findings are the first demonstration of the involvement of a protease inhibitor in neuropeptide precursor processing. The known developmental regulation of ACT in brain and significant amounts of ACT in amyloid plaques of Alzheimer's disease suggest a possible role for PTP in the maturation of peptidergic neurons.

Incorporation of 15 N and 14 C of methionine into the mugineic acid family of phytosiderophores in iron-deficient barley roots.

The role of methionine as a precursor in mugineic acid (MA) biosynthesis was studied by feeding 15 N-ammonium sulfate, 14 C-amino acids, and [1-14 C, 15 N]-methionine to iron-deficient barley roots (Hordeum vulgare L. cv. Minorimugi), grown hydroponically. The incorporation of isotopes into amino acids was also examined. Methionine appears to be the most efficient precursor of the mugineic acid family (MAs) of phytosiderophores; homoserine was also incorporated into the MAs, but other amino acids such as glutamate, alanine, and γ-amino butyric acid did not act as precursors of MAs. Carbon-14 and 15 N of methionine were incorporated into MAs. This specific incorporation of 14 C and 15 N indicated that the nitrogen atoms of MAs were derived from two molecules of methionine. It is suggested that deoxymugineic acid (DMA) is probably the first phytosiderophore to be synthesized on the biosynthetic pathway of MAs.

Methionine but Not Folinic Acid or Vitamin B-12 Alters the Frequency of Neural Tube Defects in Axd Mutant Mice

AbstractThe Axd (axial defects) mutation, which causes open neural tube defects (NTD) in 25–30% of d 14 mouse embryos of heterozygous (Axd/+) matings and curly tails (CT) in 31%, can be useful in studying neurovertebral morphogenesis. Current interest focuses on the role of methionine in neurulation, because supplementation of dams with this essential amino acid (70 mg/kg body wt) has been shown to reduce by 41% the incidence of NTD among embryos of Axd/+ × Axd/+ crosses when administered on d 8 and 9 of pregnancy. The present experiments were undertaken to determine whether supplementation of dams with a higher dose of methionine could effect a greater level of remediation. At a dose of 180 mg/kg body wt, the amino acid produced a reduction in NTD of 47%, similar to that produced at 70 mg/kg body wt. Supplementation of dams of reciprocal matings of Axd/+ × BALB/cByJ or CF-1 mice allowed assessment of the effects of methionine in heterozygous embryos, which exhibit CT. The amino acid had no effect on Axd/+ embryos from the BALB crosses, but the frequency of CT declined significantly among embryos of the CF-1 outcrosses. Maternal supplements of folinic acid (33 mg/kg) or vitamin B-12 (330 mg/kg) did not alter the incidence of NTD or CT among Axd embryos. No difference in methionine concentration was detected in the serum of Axd/+ and +/+ dams.

Role of methionine and formylation of initiator tRNA in initiation of protein synthesis in Escherichia coli.

We showed recently that a mutant of Escherichia coli initiator tRNA with a CAU-->CUA anticodon sequence change can initiate protein synthesis from UAG by using formylglutamine instead of formylmethionine. We further showed that coupling of the anticodon sequence change to mutations in the acceptor stem that reduced Vmax/Km(app) in formylation of the tRNAs in vitro significantly reduced their activity in initiation in vivo. In this work, we have screened an E. coli genomic DNA library in a multicopy vector carrying one of the mutant tRNA genes and have found that the gene for E. coli methionyl-tRNA synthetase (MetRS) rescues, partially, the initiation defect of the mutant tRNA. For other mutant tRNAs, we have examined the effect of overproduction of MetRS on their activities in initiation and their aminoacylation and formylation in vivo. Some but not all of the tRNA mutants can be rescued. Those that cannot be rescued are extremely poor substrates for MetRS or the formylating enzyme. Overproduction of MetRS also significantly increases the initiation activity of a tRNA mutant which can otherwise be aminoacylated with glutamine and fully formylated in vivo. We interpret these results as follows. (i) Mutant initiator tRNAs that are poor substrates for MetRS are aminoacylated in part with methionine when MetRS is overproduced. (ii) Mutant tRNAs aminoacylated with methionine are better substrates for the formylating enzyme in vivo than mutant tRNAs aminoacylated with glutamine. (iii) Mutant tRNAs carrying formylmethionine are significantly more active in initiation than those carrying formylglutamine. Consequently, a subset of mutant tRNAs which are defective in formylation and therefore inactive in initiation when they are aminoacylated with glutamine become partially active when MetRS is overproduced.