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PubMed2006

Three-dimensional structure of the bacterial cell wall peptidoglycan.

The 3D structure of the bacterial peptidoglycan, the major constituent of the cell wall, is one of the most important, yet still unsolved, structural problems in biochemistry. The peptidoglycan comprises alternating N-acetylglucosamine (NAG) and N-acetylmuramic disaccharide (NAM) saccharides, the latter of which has a peptide stem. Adjacent peptide stems are cross-linked by the transpeptidase enzymes of cell wall biosynthesis to provide the cell wall polymer with the structural integrity required by the bacterium. The cell wall and its biosynthetic enzymes are targets of antibiotics. The 3D structure of the cell wall has been elusive because of its complexity and the lack of pure samples. Herein we report the 3D solution structure as determined by NMR of the 2-kDa NAG-NAM(pentapeptide)-NAG-NAM(pentapeptide) synthetic fragment of the cell wall. The glycan backbone of this peptidoglycan forms a right-handed helix with a periodicity of three for the NAG-NAM repeat (per turn of the helix). The first two amino acids of the pentapeptide adopt a limited number of conformations. Based on this structure a model for the bacterial cell wall is proposed.

Amino Acid Sequence↗
PubMed2006

Gordonia soli sp. nov., a novel actinomycete isolated from soil.

A soil isolate, strain CC-AB07T, was characterized using a polyphasic approach. This organism had chemotaxonomic and morphological properties consistent with its classification in the genus Gordonia. 16S rRNA gene sequence analysis showed that the novel strain formed a monophyletic branch at the periphery of the evolutionary radiation occupied by the genus Gordonia, its closest neighbours being the type strains of Gordonia alkanivorans, Gordonia amicalis, Gordonia bronchialis, Gordonia desulfuricans, Gordonia polyisoprenivorans and Gordonia rhizosphera. The novel isolate was distinguished from all of these type strains using a range of phenotypic properties and by gyrB gene sequence analysis. It was evident from the genotypic and phenotypic data that strain CC-AB07T should be classified as representing a novel species in the genus Gordonia, for which the name Gordonia soli sp. nov. is proposed. The type strain is CC-AB07T (=BCRC 16810T=DSM 44995T).

Bacterial Typing Techniques↗
PubMed1979

Cell wall-bridge maintaining three dimensional structure of cell packets formed by the localized suppression of cell separation of a Micrococcus lysodeikticus (luteus) mutant.

Cell packets of Micrococcus lysodeikticus (luteus) mutant strain MT grown in medium supplemented with trypsin consisted of a tetrad as the unit structure. An interstice was observed between the unit-tetrads, and a three dimensional structure of cell packets was maintained by the cell wall-bridge along the rim of the cell packets which linked each unit-tetrad. This unique structure of strain MT cell packets seemed to occur when the cell separation was suppressed locally, i.e., when the cross wall inside the initial site of cell separation was cut off, while the wall outside the initial site of separation was not cut off but remained as a joint of the daughter cells. The mechanism of cell wall-bridge formation is discussed in connection with cell separation.

Amino Acids↗
PubMed2005

Two chemically distinct pools of organic nitrogen accumulate in the ocean.

The chemical dynamics of marine dissolved organic nitrogen (DON), a reservoir featuring surface accumulations even in areas where nitrogen limits productivity, have yet to be resolved. We exploited differences in the acid lability of amide bonds within high-molecular-weight (HMW) DON to show that vertical DON profiles result in part from the presence of two chemically distinct pools of amide. Half of HMWDON in surface waters is present as N-acetyl amino polysaccharides. In contrast, nearly all deep-sea HMWDON, and therefore, most HMWDON, is present in amides that resist both chemical hydrolysis and biological degradation.

Amides↗
PubMed1993

Altered muropeptide composition in Staphylococcus aureus strains with an inactivated femA locus.

Tn551 inactivation of femA, a factor involved in methicillin resistance of Staphylococcus aureus, caused the production of peptidoglycan in which the fraction of monoglycyl- and serine-containing muropeptides was increased at the expense of pentaglycyl muropeptides. femA mutants have a specific block in the biosynthesis of pentaglycine cross bridges after the addition of the first glycine residue.

Amino Acid Sequence↗
PubMed1980

The atypical cell wall composition of Thermomicrobium roseum.

The cell wall of Thermomicrobium roseum, a Gram-negative, obligately thermophilic bacterium, has a composition unlike other Gram-negative thermophilic organisms. The purified cell wall was composed predominantly of a protein with a monomeric molecular weight of 75 000. The amino acid composition of this protein revealed high concentrations of proline, glutamic acid, glycine, and alanine.

Amino Acids↗
PubMed2003

Functional and biochemical analysis of Chlamydia trachomatis MurC, an enzyme displaying UDP-N-acetylmuramate:amino acid ligase activity.

Chlamydiae are unusual obligate intracellular bacteria that cause serious infections in humans. Chlamydiae contain genes that appear to encode products with peptidoglycan biosynthetic activity. The organisms are also susceptible to antibiotics that inhibit peptidoglycan synthesis. However, chlamydiae do not synthesize detectable peptidoglycan. The paradox created by these observations is known as the chlamydial anomaly. The MurC enzyme of chlamydiae, which is synthesized as a bifunctional MurC-Ddl product, is expected to possess UDP-N-acetylmuramate (UDP-MurNAc):L-alanine ligase activity. In this paper we demonstrate that the MurC domain of the Chlamydia trachomatis bifunctional protein is functionally expressed in Escherichia coli, since it complements a conditional lethal E. coli mutant possessing a temperature-sensitive lesion in MurC. The recombinant MurC domain was overexpressed in and purified from E. coli. It displayed in vitro ATP-dependent UDP-MurNAc:L-alanine ligase activity, with a pH optimum of 8.0 and dependence upon magnesium ions (optimum concentration, 20 mM). Its substrate specificity was studied with three amino acids (L-alanine, L-serine, and glycine); comparable Vmax/Km values were obtained. Our results are consistent with the synthesis of a muramic acid-containing polymer in chlamydiae with UDP-MurNAc-pentapeptide as a precursor molecule. However, due to the lack of specificity of MurC activity in vitro, it is not obvious which amino acid is present in the first position of the pentapeptide.

Alanine↗
PubMed1972

Role of the penicillin-sensitive transpeptidation reaction in attachment of newly synthesized peptidoglycan to cell walls of Micrococcus luteus.

Cell-wall preparations of Micrococcus luteus (lysodeikticus) catalyze in vitro peptidoglycan synthesis from UDP N-acetyl-D-glucosamine, UDP N-acetylmuramic acid-pentapeptide, and glycine. Newly synthesized peptidoglycan is partially cross-linked by a transpeptidation reaction with concomitant release of C-terminal D-alanine. Penicillin not only strongly inhibits release of D-alanine (98% at 1 mug/ml), but also markedly inhibits incorporation of acetylglucosamine and N-acetylmuramic acid-pentapeptide into the preformed cell-wall peptidoglycan. The simplest explanation for the results is that incorporation of newly synthesized strands of peptidoglycan and their attachment to "older" cell-wall peptidoglycan proceeds mainly by transpeptidation and that transglycosylation is responsible only for part of the elongation of the pre-existing peptidoglycan. Another possibility is that incorporation occurs by transglycosylation, but it cannot continue without concurrent formation of peptide cross-bridges.

Amino Acids↗
PubMed1972

Regulation of the bacterial cell wall: isolation and characterization of peptidoglycan mutants of Staphylococcus aureus.

Temperature-sensitive mutants of Staphylococcus aureus H which require 1.0 m NaCl for growth at 42 C can be divided into two major classes. Most of the mutants (class A) do not accumulate nucleotide precursors of cell wall biosynthesis in the absence of salt at the nonpermissive temperatures, whereas the class B mutants accumulate these precursors. The most extensively studied mutant RUS 1 (carrying peg-1) is defective in biosynthesis of peptidoglycan at the nonpermissive conditions as evidenced by: (i) reduced incorporation of cell wall precursors into peptidoglycan; (ii) accumulation of the nucleotide, uridine diphosphate (UDP) muramyl-l-alanyl-d-glutamic acid; (iii) reduced specific activity of UDP N-acetylmuramyl (MurNAc)-l-alanyl-d-glutamate: l-lysine ligase (EC 6.3.2.7); and (iv) an increased susceptibility to lysis with sodium dodecyl sulfate. Addition of 1.0 m NaCl reverses these defects with the exception of the specific activity of UDP-MurNAc-l-alanyl-d-glutamate: l-lysine ligase. Nevertheless, the structure of the cell wall is normal at the nonpermissive conditions if 1.0 m NaCl is present. An alteration in the binding of a fluorescent dye, 8-anilino-1-napthalene-4-sulfonic acid at the nonpermissive conditions in the absence of 1.0 m NaCl suggests that there may also be defects in the membrane in this strain.

Amino Acids↗