Fast enantiomeric separation of amino acids using liquid chromatography/mass spectrometry on a chiral crown ether stationary phase

Fast enantiomeric separation of amino acids was studied by liquid chromatography/mass spectrometry (LC/MS) on a chiral crown ether stationary phase. A chiral crown ether bonded silica column (3 mm internal diameter (i.d.), 5 cm long) packed with 3 μm particles was employed instead of a 15 cm column packed with 5 μm particles used in our previous study. In addition, the extra-column variance, becoming more serious for smaller columns, was reduced by replacing 0.127 mm i.d. post-column tubes with shorter, smaller-diameter (0.0635 mm i.d.) tubes. The results demonstrated the benefits of using shorter columns packed with smaller particles and the reduction of the extra-column band broadening for fast enantiomeric separation. Finally, the enantiomeric separation of 18 pairs of proteinogenic amino acids was achieved within 2 min with a resolution (Rs) > 1.5 for each pair using an isocratic mobile phase of acetonitrile/water/trifluoroacetic acid (ACN/W/TFA) = 96/4/0.5, and a flow rate 1.2 mL/min at 30°C. This is the highest throughput method for simultaneous chiral separation of all proteinogenic amino acids except proline to date.

Antimicrobial peptide KSL-W and analogues: Promising agents to control plant diseases

Recent strong restrictions on the use of pesticides has prompted the search for safer alternatives, being antimicrobial peptides promising candidates. Herein, with the aim of identifying new agents, 15 peptides reported as plant defense elicitors, promiscuous, multifunctional or antimicrobial were selected and tested against six plant pathogenic bacteria of economic importance. Within this set, KSL-W (KKVVFWVKFK-NH2) displayed high antibacterial activity against all the tested pathogens, low hemolysis and low phytotoxicity in tobacco leaves. This peptide was taken as a lead and 49 analogues were designed and synthesized, including N-terminal deletion sequences, peptides incorporating a d-amino acid and lipopeptides. The screening of these sequences revealed that a nine amino acid length was the minimum for activity. The presence of a d-amino acid significantly decreased the hemolysis and endowed KSL-W with the capacity to induce the expression of defense-related genes in tomato plants. The incorporation of an acyl chain led to sequences with high activity against Xanthomonas strains, low hemolysis and phytotoxicity. Therefore, this study demonstrates that KSL-W constitutes an excellent candidate as new agent to control plant diseases and can be considered as a lead to develop derivatives with multifunctional properties, including antimicrobial and plant defense elicitation.

Isolation of a peptide containing d-amino acid residues that inhibits the α-helix-mediated p53-MDM2 interaction from a one-bead one-compound library

α-Helix-mediated protein-protein interactions (PPIs) are important targets in biological research and drug development. Peptides containing d-amino acid residues are attractive molecules for inhibiting α-helix-mediated PPIs because of their wide surface area and high protease resistance. In this study, a peptide library was constructed using a one-bead one-compound format designed to isolate left-handed α-helical peptides, which are promising molecules as inhibitors of α-helix-mediated PPIs. Screening of the library against an α-helix-mediated PPI between MDM2 and p53 yielded an inhibitor of the PPI. Design and screening of the library, and biochemical and spectroscopic studies of the discovered peptide are presented.

Inhibition of biofilm formation by D-tyrosine: Effect of bacterial type and D-tyrosine concentration

D-Tyrosine inhibits formation and triggers disassembly of bacterial biofilm and has been proposed for biofouling control applications. This study probes the impact of D-tyrosine in different biofilm formation stages in both G+ and G- bacteria, and reveals a non-monotonic correlation between D-tyrosine concentration and biofilm inhibition effect. In the attachment stage, cell adhesion was studied in a flow chamber, where D-tyrosine caused significant reduction in cell attachment. Biofilms formed by Pseudomonas aeruginosa and Bacillus subtilis were characterized by confocal laser scanning microscopy as well as quantitative analysis of cellular biomass and extracellular polymeric substances. D-Tyrosine exhibited strong inhibitive effects on both biofilms with an effective concentration as low as 5 nM; the biofilms responded to D-tyrosine concentration change in a non-monotonic, bi-modal pattern. In addition, D-tyrosine showed notable and different impact on EPS production by G+ and G- bacteria. Extracellular protein was decreased in P. aeruginosa biofilms, but increased in those of B. subtilis. Exopolysaccharides production by P. aeruginosa was increased at low concentrations and reduced at high concentrations while no impact was found in B. subtilis. These results suggest that distinct mechanisms are at play at different D-tyrosine concentrations and they may be species specific. Dosage of D-tyrosine must be carefully controlled for biofouling control applications.

Extra-facile chiral separation of amino acid enantiomers by LC-TOFMS analysis

An extra-facile chiral liquid chromatography-time of flight mass spectrometry (LC-TOFMS) analytical method of amino acid enantiomers has been developed without a derivatization process. The enantioseparation of eighteen proteinogenic amino acids (except for proline) was simultaneously performed using a combination of a chiral column (CROWNPAK CR-I(+)) and a TOFMS within 15 min. An isocratic condition of a simple mobile phase comprising acetonitrile/water/trifluoroacetic acid (96/4/0.5) gave baseline separation of all underivatized amino acid enantiomers on the chiral column.

Enantioselective analysis of D- and L-amino acids from mouse macrophages using high performance liquid chromatography

The intrinsic D-amino acid profile of mouse macrophages extracted from the peritoneal cavity was analyzed using high performance liquid chromatography. Six D-amino acids (D-Asp, D-Ser, D-Ala, D-Leu, D-Gln and D-Lys) were detected in cell lysates of mouse macrophages. The content and the D/D+L ratio differed depending on the type of D-amino acid and were approximately 3.5-22 nmol/g cells, and approximately 1-20%, respectively. The D-amino acid composition of RAW 264.7 cells, which is a model macrophage cell line, was similar to that of the mouse macrophage. These results suggest that macrophages and RAW 264.7 cells with macrophage-like functions have a similar D-amino acid profile.

Immunohistochemical localization of D-β-aspartic acid-containing proteins in pterygium

Biologically uncommon D-β-aspartic acid (D-β-Asp) residues have been reported to accumulate in organs affected by age-related disorders. In the present study, we investigated the localization of D-β-Asp-containing proteins in cases of pterygium, one of the most prominent age-related ocular conditions. Immunohistochemical localization of D-β-Asp-containing proteins was investigated in surgical specimens of pterygium from 20 patients and control specimens from 10 patients. Strong immunoreactivity to D-β-Asp-containing proteins was observed in subepithelial elastotic lesions and surrounding collagenous lesions from all surgical specimens with pterygia. In contrast, no immunoreactivity to D-β-Asp-containing proteins was seen in pterygium-free specimens. D-β-Asp-containing proteins are produced in organs as they are affected by the aging process. In addition, conversion of L- to D-aspartyl residues is accelerated by ultraviolet (UV) irradiation. Since pterygia can form due to aging or UV exposure, it is reasonable to find D-β-Asp-containing proteins in specimens with pterygia. Furthermore, since D-β-Asp is a non-native amino acid, D-β-Asp-containing proteins may be recognized as allogeneic antigens. Therefore, D-β-Asp-containing proteins in pterygia may responsible for the fibrovascular changes seen in the disorder.

Optimization and validation of a chiral GC-MS method for the determination of free D-amino acids ratio in human urine: application to a gestational diabetes mellitus study

Gestational Diabetes Mellitus (GDM) is defined as glucose intolerance with onset or first recognition during pregnancy. It is affecting approximately up to 14% of all pregnancies with an increasing tendency. GDM has been related to relevant short-term and long-term health complications for both mother and offspring. Recent studies strongly emphasized the role of several essential amino acids in the pathogenesis of obesity and highlighted their strong correlation with insulin resistance, but there are no references related to modifications in D-AAs in biological fluids. As D-AA elimination proceeds mainly by renal excretion, urine was the selected sample to evaluate the alterations in free D-AAs ratio in a GDM study. Only 1 mL of first void urine or standard solution was required for purification, by using a Discovery DSC-SCX SPE cartridge (500 mg/3 mL) and derivatization into their N(O)-pentafluoropropionyl amino acid 2-propyl esters. Enantiomeric separation was carried out by GC-MS on a Chirasil-L-Val N-propionyl-L-valine-tert-butylamide polysiloxane fused-silica capillary column (25 m×0.25 mm I.D., 0.12 μm film thickness, Agilent Technologies, Waldbronn, Germany), under programmed temperature elution. Detection was performed with an ion trap mass analyzer, operating in the full scan mode in the m/z 50-350 range. 14 pairs of derivatives of D-and L-AAs were separated. The steps of sample preparation, derivatization and GC-MS conditions were optimized for both urine and standards. Several conditions affecting the SPE procedure, such as sorbent mass/volume ratio of the cartridge, sample dilution and pH, were optimized. Volume of reagents and solvents and reaction temperature and time were also tested for the derivatization. Regarding the GC-MS parameters, split ratio, temperature program and mass range were optimized. The final method was validated in terms of linearity, sensitivity, accuracy and precision for D-Ala, D-Pro, D-Ser, D-Met, D-Phe, D-Glu, D-Orn and D-Lys. Identification of AAs in urine samples was based on retention time and mass spectra. Urine from 20 women with GDM and 20 pregnant women with normal glucose tolerance (after 2-h 75-g oral glucose tolerance test), matched according to the week of gestation and age (22-28 week of gestation and age 24-37 years), were enrolled into the study. %D-Relative amounts were determined for Ala, Val, Thr, Ser, Leu, Asx (Asp+Asn), Glx (Glu+Gln), Met, Phe, Tyr, Orn and Lys. Statistically significant differences (p<0.05) were observed only for D-Phe and higher values were found in the GDM group. It is possible that D-Phe could be involved in metabolic/signaling pathways to compensate early stages of insulin resistance, although further work is necessary to confirm this hypothesis.

Chiral amino acid analysis of Japanese traditional Kurozu and the developmental changes during earthenware jar fermentation processes

Enantioselective amino acid metabolome analysis of the Japanese traditional black vinegars (amber rice vinegar, Kurozu) was performed using two-dimensional high-performance liquid chromatography combining a microbore-monolithic ODS column and narrowbore-enantioselective columns. d-Amino acids, the enantiomers of widely observed l-amino acids, are currently paid attention as novel physiologically active substances, and the foodstuffs and beverages containing high amounts of d-amino acids are the subjects of interest. In the present study, the amino acid enantiomers were determined by two-dimensional HPLC techniques after pre-column fluorescence derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole. In the first dimension, the amino acid enantiomers are separated as their d plus l mixtures by the reversed-phase mode, then the d-amino acids and their l-counterparts are separately determined in the second dimension by the enantioselective columns. As a result, large amounts of d-Ala (800-4000nmol/mL), d-Asp (200-400nmol/mL) and d-Glu (150-500nmol/mL) were observed in some of the traditionally produced Kurozu vinegars. Relatively large or small amounts of d-Ser (50-100nmol/mL), d-Leu (10-50nmol/mL) and d-allo-Ile (less than 20nmol/mL) were also present in these samples. Developmental changes in the d-amino acid amounts during the fermentation and aging processes have also been investigated.

Planarian D-amino acid oxidase is involved in ovarian development during sexual induction

To elucidate the molecular mechanisms underlying switching from asexual to sexual reproduction, namely sexual induction, we developed an assay system for sexual induction in the hermaphroditic planarian species Dugesia ryukyuensis. Ovarian development is the initial and essential step in sexual induction, and it is followed by the formation of other reproductive organs, including the testes. Here, we report a function of a planarian D-amino acid oxidase, Dr-DAO, in the control of ovarian development in planarians. Asexual worms showed significantly more widespread expression of Dr-DAO in the parenchymal space than did sexual worms. Inhibition of Dr-DAO by RNAi caused the formation of immature ovaries. In addition, we found that feeding asexual worms 5 specific D-amino acids could induce the formation of immature ovaries that are similar to those observed in Dr-DAO knockdown worms, suggesting that Dr-DAO inhibits the formation of immature ovaries by degrading these D-amino acids. Following sexual induction, Dr-DAO expression was observed in the ovaries. The knockdown of Dr-DAO during sexual induction delayed the maturation of the other reproductive organs, as well as ovary. These findings suggest that Dr-DAO acts to promote ovarian maturation and that complete sexual induction depends on the production of mature ovaries. We propose that Dr-DAO produced in somatic cells prevents the onset of sexual induction in the asexual state, and then after sexual induction, the female germ cells specifically produce Dr-DAO to induce full maturation. Therefore, Dr-DAO produced in somatic and female germline cells may play different roles in sexual induction.