alanyllactate and alanylalanine

Induction of vancomycin resistance in vancomycin-resistant enterococci (VRE) involves replacement of the d-Ala-d-Ala terminus of peptidoglycan (PG) stems with d-Ala-d-Lac, dramatically reducing the binding affinity of vancomycin for lipid II. Effects from vancomycin resistance induction in Enterococcus faecalis (ATCC 51299) were characterized using a combined solid-state nuclear magnetic resonance (NMR) and liquid chromatography-mass spectrometry (LC-MS) analysis. Solid-state NMR directly measured the total amounts of d-Lac and l,d-Ala metabolized from [2-

Topics: Alanine; Anti-Bacterial Agents; Cell Wall; Dipeptides; Endopeptidases; Enterococcus faecalis; Lactates; Magnetic Resonance Spectroscopy; Mass Spectrometry; Peptidoglycan; Uridine Diphosphate N-Acetylmuramic Acid; Vancomycin; Vancomycin Resistance

The total synthesis of two key analogues of vancomycin containing single-atom exchanges in the binding pocket (residue 4 amidine and thioamide) are disclosed as well as their peripherally modified (4-chlorobiphenyl)methyl (CBP) derivatives. Their assessment indicates that combined pocket amidine and CBP peripherally modified analogues exhibit a remarkable spectrum of antimicrobial activity (VSSA, MRSA, VanA and VanB VRE) and impressive potencies (MIC = 0.06-0.005 μg/mL) against both vancomycin-sensitive and -resistant bacteria and likely benefit from two independent and synergistic mechanisms of action. Like vancomycin, such analogues are likely to display especially durable antibiotic activity not prone to rapidly acquired clinical resistance.

Topics: Alanine; Binding Sites; Dipeptides; Lactates; Molecular Conformation; Stereoisomerism; Vancomycin

To seek vancomycin analogs with broader antibacterial activity, effects of backbone modifications for the agylcon 2 on binding with D-Ala-D-Ala- and D-Ala-D-Lac-containing peptides were investigated by Monte Carlo/free energy perturbation (MC/FEP) calculations. The experimental trend in binding affinities for 2 with three tripeptides was well reproduced. Possible modifications of the peptide bond between residues 4 and 5 were then considered, specifically for conversion of the OCNH linkage to CH(2)NH(2)(+) (6), FCCH (7), HCCH (8), and HNCO (9). The MC/FEP results did not yield binding improvements for 7, 8, and 9, though the fluorovinyl replacement is relatively benign. The previously reported analog 6 remains as the only variant that exhibits improved affinity for the D-Ala-D-Lac sequence and acceptable affinity for the D-Ala-D-Ala sequence.

Topics: Alanine; Anti-Bacterial Agents; Dipeptides; Lactates; Models, Molecular; Molecular Structure; Peptides; Stereoisomerism; Structure-Activity Relationship; Vancomycin Resistance

The recent rise of vancomycin-resistant enterococci (VRE) has given new impetus to the study of the binding between glycopeptide antibiotics and bacterial cell wall termini. Here, we report on an extensive first principles investigation of the binding of vancomycin and teicoplanin with d-Ala-d-Lac (characteristic of VREs) and d-Ala-d-Ala (characteristic of non-VREs). Binding of both antibiotics to d-Ala-d-Ala was found to be stronger by about 3-5 kcal/mol and due primarily to the oxygen-oxygen lone-pair repulsion characteristic of the antibiotic/d-Ala-d-Lac complex. These results are in good agreement with recent experimental findings.

Topics: Alanine; Anti-Bacterial Agents; Bacteria; Cell Wall; Dipeptides; Kinetics; Lactates; Teicoplanin; Thermodynamics; Vancomycin

The Gram-positive bacterium Leuconostoc mesenteroides, ATCC 8293, is intrinsically resistant to the antibiotic vancomycin. This phenotype correlates with substitution of D-Ala-D-lactate (D-Ala-D-Lac) termini for D-Ala-D-Ala termini in peptidoglycan intermediates in which the depsipeptide has much lower affinity than the dipeptide for vancomycin binding. Overproduction of the L. mesenteroides D-Ala-D-Ala ligase (LmDdl) 2 in E. coli and its purification to approximately 90% homogeneity allow demonstration that the LmDdl2 does have both depsipeptide and dipeptide ligase activity. Recently, we reported that mutation of an active site tyrosine (Tyr), Tyr216, to phenylalanine (Phe) in the E. coli DdlB leads to gain of D-Ala-D-Lac depsipeptide ligase activity in that enzyme. The vancomycin-resistant LmDdl2 has a Phe at the equivalent site, Phe261. To test the prediction that a Tyr residue predicts dipeptide ligase while an Phe residue predicts both depsipeptide and dipeptide ligase activity, the F261Y mutant protein of LmDdl2 was constructed and purified to approximately 90% purity. F216Y LmDdl2 showed complete loss of the ability to couple D-Lac but retained D-Ala-D-Ala dipeptide ligase activity. The Tyr-->Phe substitution on the active site omega-loop in D-Ala-D-Ala ligases is thus a molecular indicator of both the ability to make D-Ala-D-Lac and intrinsic resistance to the vancomycin class of glycopeptide antibiotics.

Topics: Alanine; Amino Acid Sequence; Binding Sites; Dipeptides; Drug Resistance, Microbial; Lactates; Leuconostoc; Models, Molecular; Molecular Sequence Data; Peptide Synthases; Phenotype; Phenylalanine; Point Mutation; Sequence Alignment; Tyrosine; Vancomycin

Cloning and nucleotide sequencing indicated that transposon Tn1546 from Enterococcus faecium BM4147 encodes a 23,365 Da protein, VanX, required for glycopeptide resistance. The vanX gene was located downstream from genes encoding the VanA ligase and the VanH dehydrogenase which synthesize the depsipeptide D-alanyl-D-lactate (D-Ala-D-Lac). In the presence of ramoplanin, an Enterococcus faecalis JH2-2 derivative producing VanH, VanA and VanX accumulated mainly UDP-MurNAc-L-Ala-gamma-D-Glu-L-Lys-D-Ala-D-Lac (pentadepsipeptide) and small amounts of UDP-MurNAc-L-Ala-gamma-D-Glu-L-Lys-D-Ala-D-Ala (pentapeptide) in the ratio 49:1. Insertional inactivation of vanX led to increased synthesis of pentapeptide with a resulting change in the ratio of pentadepsipeptide: pentapeptide to less than 1:1. Expression of vanX in E. faecalis and Escherichia coli resulted in production of a D,D-dipeptidase that hydrolysed D-Ala-D-Ala. Pentadepsipeptide, pentapeptide and D-Ala-D-Lac were not substrates for the enzyme. These results establish that VanX is required for production of a D,D-dipeptidase that hydrolyses D-Ala-D-Ala, thereby preventing pentapeptide synthesis and subsequent binding of glycopeptides to D-Ala-D-Ala-containing peptidoglycan precursors at the cell surface.

Topics: Alanine; Amino Acid Sequence; Bacterial Proteins; Base Sequence; Carbon-Oxygen Ligases; Dipeptides; DNA Transposable Elements; Drug Resistance, Microbial; Enterococcus faecium; Gene Expression Regulation, Bacterial; Genes, Bacterial; Hydrolysis; Lactates; Ligases; Molecular Sequence Data; Peptidoglycan; Protein Kinases; Pyruvates; Pyruvic Acid; Serine-Type D-Ala-D-Ala Carboxypeptidase; Teicoplanin; Transcription Factors; Vancomycin