Cooperativity of peptidoglycan synthases active in bacterial cell elongation.

in Molecular Microbiology (2012), 85(1), 179-94

Growth of the bacterial cell wall peptidoglycan sacculus requires the co-ordinated activities of peptidoglycan synthases, hydrolases and cell morphogenesis proteins, but the details of these interactions ... [more ▼]

Growth of the bacterial cell wall peptidoglycan sacculus requires the co-ordinated activities of peptidoglycan synthases, hydrolases and cell morphogenesis proteins, but the details of these interactions are largely unknown. We now show that the Escherichia coli peptidoglycan glycosyltrasferase-transpeptidase PBP1A interacts with the cell elongation-specific transpeptidase PBP2 in vitro and in the cell. Cells lacking PBP1A are thinner and initiate cell division later in the cell cycle. PBP1A localizes mainly to the cylindrical wall of the cell, supporting its role in cell elongation. Our in vitro peptidoglycan synthesis assays provide novel insights into the cooperativity of peptidoglycan synthases with different activities. PBP2 stimulates the glycosyltransferase activity of PBP1A, and PBP1A and PBP2 cooperate to attach newly synthesized peptidoglycan to sacculi. PBP2 has peptidoglycan transpeptidase activity in the presence of active PBP1A. Our data also provide a possible explanation for the depletion of lipid II precursors in penicillin-treated cells. [less ▲]

Small molecule inhibitors of peptidoglycan synthesis targeting the lipid II precursor.

in Biochemical Pharmacology (2011), 81(9), 1098-105

Bacterial peptidoglycan glycosyltransferases (GTs) of family 51 catalyze the polymerization of the lipid II precursor into linear peptidoglycan strands. This activity is essential to bacteria and ... [more ▼]

Bacterial peptidoglycan glycosyltransferases (GTs) of family 51 catalyze the polymerization of the lipid II precursor into linear peptidoglycan strands. This activity is essential to bacteria and represents a validated target for the development of new antibacterials. Application of structure-based virtual screening to the National Cancer Institute library using eHits program and the structure of the glycosyltransferase domain of the Staphylococcus aureus penicillin-binding protein 2 resulted in the identification of two small molecules analogues 5, a 2-[1-[(2-chlorophenyl)methyl]-2-methyl-5-methylsulfanylindol-3-yl]ethanamine and 5b, a 2-[1-[(3,4-dichlorophenyl)methyl]-2-methyl-5-methylsulfanylindol-3-yl]ethanamine that exhibit antibacterial activity against several Gram-positive bacteria but were less active on Gram-negative bacteria. The two compounds inhibit the activity of five GTs in the micromolar range. Investigation of the mechanism of action shows that the compounds specifically target peptidoglycan synthesis. Unexpectedly, despite the fact that the compounds were predicted to bind to the GT active site, compound 5b was found to interact with the lipid II substrate via the pyrophosphate motif. In addition, this compound showed a negatively charged phospholipid-dependent membrane depolarization and disruption activity. These small molecules are promising leads for the development of more active and specific compounds to target the essential GT step in cell wall synthesis. [less ▲]

Optimization of conditions for the glycosyltransferase activity of penicillin-binding protein 1a from Thermotoga maritima.

in FEBS Journal (2010), 277(20), 4290-8

Cell wall biosynthesis is a key target for antibacterial drugs. The major constituent of the bacterial wall, peptidoglycan, is a netlike polymer responsible for the size and shape of the cell and for ... [more ▼]

Cell wall biosynthesis is a key target for antibacterial drugs. The major constituent of the bacterial wall, peptidoglycan, is a netlike polymer responsible for the size and shape of the cell and for resisting osmotic pressure. It consists of glycan chains of repeating disaccharide units cross-linked through short peptide chains. Peptidoglycan assembly is catalyzed by the periplasmic domain of bifunctional class A penicillin-binding proteins. Cross-linking of the peptide chains is catalyzed by their transpeptidase module, which can be inhibited by the most widely used antibiotics, the beta-lactams. In contrast, no drug in clinical use inhibits the polymerization of the glycan chains, catalyzed by their glycosyltransferase module, although it is an obvious target. We report here the purification of the ectodomain of the class A penicillin-binding protein 1a from Thermotoga maritima (Tm-1a*), expressed recombinantly in Escherichia coli. A detergent screen showed that detergents with shorter aliphatic chains were better solubilizers. Cyclohexyl-hexyl-beta-D-maltoside-purified Tm-1a* was found to be monomeric and to have improved thermal stability. A miniaturized, multiwell continuous fluorescence assay of the glycosyltransferase activity was used to screen for optimal reaction conditions. Tm-1a* was active as a glycosyltransferase, catalyzing the formation of glycan chains up to 16 disaccharide units long. Our results emphasize the importance of the detergent in preparing a stable monomeric ectodomain of a class A penicillin-binding protein. Our assay could be used to screen collections of compounds for inhibitors of peptidoglycan glycosyltransferases that could serve as the basis for the development of novel antibiotics. [less ▲]

The Monofunctional Glycosyltransferase of Escherichia Coli Localizes to the Cell Division Site and Interacts with Penicillin-Binding Protein 3, FtsW, and FtsN

in Journal of Bacteriology (2008), 190(5), 1831-4

The monofunctional peptidoglycan glycosyltransferase (MtgA) catalyzes glycan chain elongation of the bacterial cell wall. Here we show that MtgA localizes at the division site of Escherichia coli cells ... [more ▼]

The monofunctional peptidoglycan glycosyltransferase (MtgA) catalyzes glycan chain elongation of the bacterial cell wall. Here we show that MtgA localizes at the division site of Escherichia coli cells that are deficient in PBP1b and produce a thermosensitive PBP1a and is able to interact with three constituents of the divisome, PBP3, FtsW, and FtsN, suggesting that MtgA may play a role in peptidoglycan assembly during the cell cycle in collaboration with other proteins. [less ▲]

Peptidoglycan Glycosyltransferase Inhibition: New Perspectives for An Old Target.

in Anti-Infective Agents in Medicinal Chemistry (2008)

The essential cell division protein FtsN interacts with the murein (peptidoglycan) synthase PBP1B in Escherichia coli

in Journal of Biological Chemistry (2007), 282(50), 36394-36402

Bacterial cell division requires the coordinated action of cell division proteins and murein (peptidoglycan) synthases. Interactions involving the essential cell division protein FtsN and murein synthases ... [more ▼]

Bacterial cell division requires the coordinated action of cell division proteins and murein (peptidoglycan) synthases. Interactions involving the essential cell division protein FtsN and murein synthases were studied by affinity chromatography with membrane fraction. The murein synthases PBP1A, PBP1B, and PBP3 had an affinity to immobilized FtsN. FtsN and PBP3, but not PBP1A, showed an affinity to immobilized PBP1B. The direct interaction between FtsN and PBP1B was confirmed by pulldown experiments and surface plasmon resonance. The interaction was also detected by bacterial two-hybrid analysis. FtsN and PBP1B could be cross-linked in intact cells of the wild type and in cells depleted of PBP3 or FtsW. FtsN stimulated the in vitro murein synthesis activities of PBP1B. Thus, FtsN could have a role in controlling or modulating the activity of PBP1B during cell division in Escherichia coli. [less ▲]

Characterization of the bifunctional glycosyltransferase/acyltransferase penicillin-binding protein 4 of Listeria monocytogenes

in Journal of Bacteriology (2006), 188(5), 1875-1881

Multimodular penicillin-binding proteins (PBPs) are essential enzymes responsible for bacterial cell wall peptidoglycan (PG) assembly. Their glycosyltransferase activity catalyzes glycan chain elongation ... [more ▼]

Multimodular penicillin-binding proteins (PBPs) are essential enzymes responsible for bacterial cell wall peptidoglycan (PG) assembly. Their glycosyltransferase activity catalyzes glycan chain elongation from lipid II substrate (undecaprenyl-pyrophosphoryi-N-acetylglucosamine-N-acetylmuramic acid-pentapeptide), and their transpeptidase activity catalyzes cross-linking between peptides carried by two adjacent glycan chains. Listeria monocytogenes is a food-borne pathogen which exerts its virulence through secreted and cell wall PG-associated virulence factors. This bacterium has five PBPs, including two bifunctional glycosyltransferase/transpeptidase class A PBPs, namely, PBP1 and PBP4. We have expressed and purified the latter and have shown that it binds penicillin and catalyzes in vitro glycan chain polymerization with an efficiency of 1,400 M-1 s(-1) from Escherichia coli lipid II substrate. PBP4 also catalyzes the aminolysis (D-Ala as acceptor) and hydrolysis of the thiolester donor substrate benzoyl-Gly-thioglycolate, indicating that PBP4 possesses both transpeptidase and carboxyeptidase activities. Disruption of the gene lmo2229 encoding PBP4 in L. monocytogenes EGD did not. p have any significant effect on growth rate, peptidoglycan composition, cell morphology, or sensitivity to beta-lactam antibiotics but did increase the resistance of the mutant to moenomycin. [less ▲]

The Iq motif defines the conformation of the interacting calmodullin

in Biophysical Journal (2004, January), 86

Structural basis of protein phosphatase 1 regulation

in Nature (2004), 429(6993), 780-4

The coordinated and reciprocal action of serine/threonine (Ser/Thr) protein kinases and phosphatases produces transient phosphorylation, a fundamental regulatory mechanism for many biological processes ... [more ▼]

The coordinated and reciprocal action of serine/threonine (Ser/Thr) protein kinases and phosphatases produces transient phosphorylation, a fundamental regulatory mechanism for many biological processes. The human genome encodes a far greater number of Ser/Thr protein kinases than of phosphatases. Protein phosphatase 1 (PP1), in particular, is ubiquitously distributed and regulates a broad range of cellular functions, including glycogen metabolism, cell-cycle progression and muscle relaxation. PP1 has evolved effective catalytic machinery but lacks substrate specificity. Substrate specificity is conferred upon PP1 through interactions with a large number of regulatory subunits. The regulatory subunits are generally unrelated, but most possess the RVxF motif, a canonical PP1-binding sequence. Here we reveal the crystal structure at 2.7 A resolution of the complex between PP1 and a 34-kDa N-terminal domain of the myosin phosphatase targeting subunit MYPT1. MYPT1 is the protein that regulates PP1 function in smooth muscle relaxation. Structural elements amino- and carboxy-terminal to the RVxF motif of MYPT1 are positioned in a way that leads to a pronounced reshaping of the catalytic cleft of PP1, contributing to the increased myosin specificity of this complex. The structure has general implications for the control of PP1 activity by other regulatory subunits. [less ▲]

Two distinct myosin light chain structures are induced by specific variations within the bound IQ motifs-functional implications

in EMBO Journal (2003), 22(3), 362-71

IQ motifs are widespread in nature. Mlc1p is a calmodulin-like myosin light chain that binds to IQ motifs of a class V myosin, Myo2p, and an IQGAP-related protein, Iqg1p, playing a role in polarized ... [more ▼]

IQ motifs are widespread in nature. Mlc1p is a calmodulin-like myosin light chain that binds to IQ motifs of a class V myosin, Myo2p, and an IQGAP-related protein, Iqg1p, playing a role in polarized growth and cytokinesis in Saccharomyces cerevisiae. The crystal structures of Mlc1p bound to IQ2 and IQ4 of Myo2p differ dramatically. When bound to IQ2, Mlc1p adopts a compact conformation in which both the N- and C-lobes interact with the IQ motif. However, in the complex with IQ4, the N-lobe no longer interacts with the IQ motif, resulting in an extended conformation of Mlc1p. The two light chain structures relate to two distinct subfamilies of IQ motifs, one of which does not interact with the N-lobes of calmodulin-like light chains. The correlation between light chain structure and IQ sequence is demonstrated further by sedimentation velocity analysis of complexes of Mlc1p with IQ motifs from Myo2p and Iqg1p. The resulting 'free' N-lobes of myosin light chains in the extended conformation could mediate the formation of ternary complexes during protein localization and/or partner recruitment. [less ▲]