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Related Articles

Structure and Inhibitor Specificity of L,D-Transpeptidase (LdtMt2) from Mycobacterium tuberculosis and Antibiotic Resistance: Calcium Binding Promotes Dimer Formation.

AAPS J. 2018 Mar 09;20(2):44

Authors: Gokulan K, Khare S, Cerniglia CE, Foley SL, Varughese KI

Abstract
The final step of peptidoglycan (PG) synthesis in all bacteria is the formation of cross-linkage between PG-stems. The cross-linking between amino acids in different PG chains gives the peptidoglycan cell wall a 3-dimensional structure and adds strength and rigidity to it. There are two distinct types of cross-linkages in bacterial cell walls. D,D-transpeptidase (D,D-TPs) generate the classical 4➔3 cross-linkages and the L,D-transpeptidase (L,D-TPs) generate the 3➔3 non-classical peptide cross-linkages. The present study is aimed at understanding the nature of drug resistance associated with L,D-TP and gaining insights for designing novel antibiotics against multi-drug resistant bacteria. Penicillin and cephalosporin classes of β-lactams cannot inhibit L,D-TP function; however, carbapenems inactivate its function. We analyzed the structure of L,D-TP of Mycobacterium tuberculosis in the apo form and in complex with meropenem and imipenem. The periplasmic region of L,D-TP folds into three domains. The catalytic residues are situated in the C-terminal domain. The acylation reaction occurs between carbapenem antibiotics and the catalytic Cys-354 forming a covalent complex. This adduct formation mimics the acylation of L,D-TP with the donor PG-stem. A novel aspect of this study is that in the crystal structures of the apo and the carbapenem complexes, the N-terminal domain has a muropeptide unit non-covalently bound to it. Another interesting observation is that the calcium complex crystallized as a dimer through head and tail interactions between the monomers.

PMID: 29524047 [PubMed - in process]

Scientists on the Norwich Research Park have discovered a key mechanism by which gut bacteria colonise and adhere to their specific hosts.

How do microbes maintain their shape? This review takes a closer look at the role played by the actin homolog MreB in controlling rod-shaped bacterial growth.

The C. elegans Proteome Response to Naturally Associated Microbiome Members of the Genus Ochrobactrum.

Proteomics. 2018 Mar 07;:

Authors: Cassidy L, Petersen C, Treitz C, Dierking K, Schulenburg H, Leippe M, Tholey A

Abstract
The nematode Caenorhabditis elegans interacts with a variety of bacteria as it feeds on microbes, and a number of these both associate and persist within the worm's intestine. Host-microbe interactions in C. elegans have been analysed primarily at the transcriptome level with the host response often been monitored after challenge with pathogens. We assessed the proteome of C. elegans after growth on bacteria capable of colonising its gut, via a comparative analysis of the nematode exposed to two naturally associated Ochrobactrum spp. (MYb71, MYb237) versus C. elegans grown on E. coli OP50. A total of 4,677 C. elegans proteins were identified, 3,941 quantified. Significant alterations in protein abundances were observed for 122 proteins, 48 higher and 74 lower in abundance. We observed an increase in abundance of proteins potentially regulated via host signalling pathways, in addition to proteins involved in processing of foreign entities (e.g. lipase, proteases, glutathione metabolism). Decreased in abundance were proteins involved in both degradation and biosynthesis of amino acids, and enzymes associated with the degradation of peptidoglycan (lysozymes). The protein level differences between C. elegans grown on native microbiome members compared to the laboratory food bacterium may help to identify molecular processes involved in host-microbe interactions. This article is protected by copyright. All rights reserved.

PMID: 29513928 [PubMed - as supplied by publisher]

Related Articles

Conserved mechanism of cell-wall synthase regulation revealed by the identification of a new PBP activator in Pseudomonas aeruginosa.

Proc Natl Acad Sci U S A. 2018 Mar 05;:

Authors: Greene NG, Fumeaux C, Bernhardt TG

Abstract
Penicillin-binding proteins (PBPs) are synthases required to build the essential peptidoglycan (PG) cell wall surrounding most bacterial cells. The mechanisms regulating the activity of these enzymes to control PG synthesis remain surprisingly poorly defined given their status as key antibiotic targets. Several years ago, the outer-membrane lipoprotein EcLpoB was identified as a critical activator of Escherichia coli PBP1b (EcPBP1b), one of the major PG synthases of this organism. Activation of EcPBP1b is mediated through the association of EcLpoB with a regulatory domain on EcPBP1b called UB2H. Notably, Pseudomonas aeruginosa also encodes PBP1b (PaPBP1b), which possesses a UB2H domain, but this bacterium lacks an identifiable LpoB homolog. We therefore searched for potential PaPBP1b activators and identified a lipoprotein unrelated to LpoB that is required for the in vivo activity of PaPBP1b. We named this protein LpoP and found that it interacts directly with PaPBP1b in vitro and is conserved in many Gram-negative species. Importantly, we also demonstrated that PaLpoP-PaPBP1b as well as an equivalent protein pair from Acinetobacter baylyi can fully substitute for EcLpoB-EcPBP1b in E. coli for PG synthesis. Furthermore, we show that amino acid changes in PaPBP1b that bypass the PaLpoP requirement map to similar locations in the protein as changes promoting EcLpoB bypass in EcPBP1b. Overall, our results indicate that, although different Gram-negative bacteria activate their PBP1b synthases with distinct lipoproteins, they stimulate the activity of these important drug targets using a conserved mechanism.

PMID: 29507210 [PubMed - as supplied by publisher]

An international research team led by the Institute of Bioengineering and Nanotechnology (IBN) of the Agency for Science, Technology and Research (A*STAR) and IBM Research developed a synthetic molecule that can kill five deadly types of multidrug-resistant bacteria with limited, if any, side effects. Their new material could be developed into an antimicrobial drug to treat patients with antibiotic-resistant infections. This finding was reported in the scientific journal Nature Communications.

In vivo virulence of Mycobacterium tuberculosis depends on a single homologue of the LytR-CpsA-Psr proteins.

Sci Rep. 2018 Mar 02;8(1):3936

Authors: Malm S, Maaß S, Schaible UE, Ehlers S, Niemann S

Abstract
LytR-cpsA-Psr (LCP) domain containing proteins fulfil important functions in bacterial cell wall synthesis. In Mycobacterium tuberculosis complex (Mtbc) strains, the causative agents of tuberculosis (TB), the genes Rv3484 and Rv3267 encode for LCP proteins which are putatively involved in arabinogalactan transfer to peptidoglycan. To evaluate the significance of Rv3484 for Mtbc virulence, we generated a deletion mutant in the Mtbc strain H37Rv and studied its survival in mice upon aerosol infection. The deletion mutant failed to establish infection demonstrating that Rv3484 is essential for growth in mice. Following an initial phase of marginal replication in the lungs until day 21, the Rv3484 deletion mutant was almost eliminated by day 180 post-infectionem. Interestingly, the mutant also showed higher levels of resistance to meropenem/clavulanate and lysozyme, both targeting peptidoglycan structure. We conclude that Rv3484 is essential for Mtbc virulence in vivo where its loss of function cannot be compensated by Rv3267.

PMID: 29500450 [PubMed - in process]

Including microbiome composition in predictions of whether a person is obese can significantly improve their accuracy, according to an analysis.

A molecule produced by a strain of Staphylococcus epidermis interferes with DNA synthesis.

Tuberculosis (TB) is the leading cause of death from an infectious bacterial disease. Poor diagnostic tools to detect active disease plague TB control programs and affect patient care. Accurate detection of live Mycobacterium tuberculosis (Mtb), the causative agent of TB, could improve TB diagnosis and patient treatment. We report that mycobacteria and other corynebacteria can be specifically detected with a fluorogenic trehalose analog. We designed a 4-N,N-dimethylamino-1,8-naphthalimide–conjugated trehalose (DMN-Tre) probe that undergoes >700-fold increase in fluorescence intensity when transitioned from aqueous to hydrophobic environments. This enhancement occurs upon metabolic conversion of DMN-Tre to trehalose monomycolate and incorporation into the mycomembrane of Actinobacteria. DMN-Tre labeling enabled the rapid, no-wash visualization of mycobacterial and corynebacterial species without nonspecific labeling of Gram-positive or Gram-negative bacteria. DMN-Tre labeling was detected within minutes and was inhibited by heat killing of mycobacteria. Furthermore, DMN-Tre labeling was reduced by treatment with TB drugs, unlike the clinically used auramine stain. Lastly, DMN-Tre labeled Mtb in TB-positive human sputum samples comparably to auramine staining, suggesting that this operationally simple method may be deployable for TB diagnosis.

Publication date: October 2018
Source:Current Opinion in Microbiology, Volume 45
Author(s): Joanna C .Evans, Valerie Mizrahi
Claiming close to two million lives each year, tuberculosis is now the leading cause of death from an infectious disease. The rise in number of Mycobacterium tuberculosis (Mtb) strains resistant to existing TB drugs has underscored the urgent need to develop new antimycobacterials with novel mechanisms of action. To meet this need, a drug pipeline has been established that is populated with new and repurposed drugs. Recent advances in identifying molecules with inhibitory activity against Mtb under conditions modelled on those encountered during infection, and in elucidating their mechanisms of action, have primed the pipeline with promising drug/target couples, hit compounds and new targets. In this review, we highlight recent advances and emerging areas of opportunity in this field.

Graphical abstract

Neither Lys- and DAP-type peptidoglycans stimulate mouse or human innate immune cells via Toll-like receptor 2.

PLoS One. 2018;13(2):e0193207

Authors: Langer M, Girton AW, Popescu NI, Burgett T, Metcalf JP, Coggeshall KM

Abstract
Peptidoglycan (PGN), a major component of bacterial cell walls, is a pathogen-associated molecular pattern (PAMP) that causes innate immune cells to produce inflammatory cytokines that escalate the host response during infection. In order to better understand the role of PGN in infection, we wanted to gain insight into the cellular receptor for PGN. Although the receptor was initially identified as Toll-like receptor 2 (TLR2), this receptor has remained controversial and other PGN receptors have been reported. We produced PGN from live cultures of Bacillus anthracis and Staphylococcus aureus and tested samples of PGN isolated during the purification process to determine at what point TLR2 activity was removed, if at all. Our results indicate that although live B. anthracis and S. aureus express abundant TLR2 ligands, highly-purified PGN from either bacterial source is not recognized by TLR2.

PMID: 29474374 [PubMed - in process]

Related Articles

Substrate binding to BamD triggers a conformational change in BamA to control membrane insertion.

Proc Natl Acad Sci U S A. 2018 03 06;115(10):2359-2364

Authors: Lee J, Sutterlin HA, Wzorek JS, Mandler MD, Hagan CL, Grabowicz M, Tomasek D, May MD, Hart EM, Silhavy TJ, Kahne D

Abstract
The β-barrel assembly machine (Bam) complex folds and inserts integral membrane proteins into the outer membrane of Gram-negative bacteria. The two essential components of the complex, BamA and BamD, both interact with substrates, but how the two coordinate with each other during assembly is not clear. To elucidate aspects of this process we slowed the assembly of an essential β-barrel substrate of the Bam complex, LptD, by changing a conserved residue near the C terminus. This defective substrate is recruited to the Bam complex via BamD but is unable to integrate into the membrane efficiently. Changes in the extracellular loops of BamA partially restore assembly kinetics, implying that BamA fails to engage this defective substrate. We conclude that substrate binding to BamD activates BamA by regulating extracellular loop interactions for folding and membrane integration.

PMID: 29463713 [PubMed - indexed for MEDLINE]

Direct observation of the influence of cardiolipin and antibiotics on lipid II binding to MurJ.

Nat Chem. 2018 Mar;10(3):363-371

Authors: Bolla JR, Sauer JB, Wu D, Mehmood S, Allison TM, Robinson CV

Abstract
Translocation of lipid II across the cytoplasmic membrane is essential in peptidoglycan biogenesis. Although most steps are understood, identifying the lipid II flippase has yielded conflicting results, and the lipid II binding properties of two candidate flippases-MurJ and FtsW-remain largely unknown. Here we apply native mass spectrometry to both proteins and characterize lipid II binding. We observed lower levels of lipid II binding to FtsW compared to MurJ, consistent with MurJ having a higher affinity. Site-directed mutagenesis of MurJ suggests that mutations at A29 and D269 attenuate lipid II binding to MurJ, whereas chemical modification of A29 eliminates binding. The antibiotic ramoplanin dissociates lipid II from MurJ, whereas vancomycin binds to form a stable complex with MurJ:lipid II. Furthermore, we reveal cardiolipins associate with MurJ but not FtsW, and exogenous cardiolipins reduce lipid II binding to MurJ. These observations provide insights into determinants of lipid II binding to MurJ and suggest roles for endogenous lipids in regulating substrate binding.

PMID: 29461535 [PubMed - in process]