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Structure of WbdD: a bifunctional kinase and methyltransferase that regulates the chain length of the O antigen in Escherichia coli O9a.

ABSTRACT: The Escherichia coli serotype O9a O-antigen polysaccharide (O-PS) is a model for glycan biosynthesis and export by the ATP-binding cassette transporter-dependent pathway. The polymannose O9a O-PS is synthesized as a polyprenol-linked glycan by mannosyltransferase enzymes located at the cytoplasmic membrane. The chain length of the O9a O-PS is tightly regulated by the WbdD enzyme. WbdD first phosphorylates the terminal non-reducing mannose of the O-PS and then methylates the phosphate, stopping polymerization. The 2.2 Å resolution structure of WbdD reveals a bacterial methyltransferase domain joined to a eukaryotic kinase domain. The kinase domain is again fused to an extended C-terminal coiled-coil domain reminiscent of eukaryotic DMPK (Myotonic Dystrophy Protein Kinase) family kinases such as Rho-associated protein kinase (ROCK). WbdD phosphorylates 2-α-d-mannosyl-d-mannose (2α-MB), a short mimic of the O9a polymer. Mutagenesis identifies those residues important in catalysis and substrate recognition and the in vivo phenotypes of these mutants are used to dissect the termination reaction. We have determined the structures of co-complexes of WbdD with two known eukaryotic protein kinase inhibitors. Although these are potent inhibitors in vitro, they do not show any in vivo activity. The structures reveal new insight into O-PS chain-length regulation in this important model system.

SUBMITTER: Hagelueken G

PROVIDER: S-EPMC3482155 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Crystallization, dehydration and experimental phasing of WbdD, a bifunctional kinase and methyltransferase from Escherichia coli O9a.

Project description:WbdD is a bifunctional kinase/methyltransferase that is responsible for regulation of lipopolysaccharide O antigen polysaccharide chain length in Escherichia coli serotype O9a. Solving the crystal structure of this protein proved to be a challenge because the available crystals belonging to space group I23 only diffracted to low resolution (>95% of the crystals diffracted to resolution lower than 4 Å and most only to 8 Å) and were non-isomorphous, with changes in unit-cell dimensions of greater than 10%. Data from a serendipitously found single native crystal that diffracted to 3.0 Å resolution were non-isomorphous with a lower (3.5 Å) resolution selenomethionine data set. Here, a strategy for improving poor (3.5 Å resolution) initial phases by density modification and cross-crystal averaging with an additional 4.2 Å resolution data set to build a crude model of WbdD is desribed. Using this crude model as a mask to cut out the 3.5 Å resolution electron density yielded a successful molecular-replacement solution of the 3.0 Å resolution data set. The resulting map was used to build a complete model of WbdD. The hydration status of individual crystals appears to underpin the variable diffraction quality of WbdD crystals. After the initial structure had been solved, methods to control the hydration status of WbdD were developed and it was thus possible to routinely obtain high-resolution diffraction (to better than 2.5 Å resolution). This novel and facile crystal-dehydration protocol may be useful for similar challenging situations.

| S-EPMC3447403 | biostudies-literature

Lipopolysaccharide O antigen size distribution is determined by a chain extension complex of variable stoichiometry in Escherichia coli O9a.

Project description:The lengths of bacterial polysaccharides can be critical for their biological function. Unlike DNA or protein synthesis, where polymer length is implicit in the nucleic acid template, the molecular mechanisms for regulating polysaccharide length are poorly understood. Two models are commonly cited: a "molecular clock" regulates length by controlling the duration of the polymer extension process, whereas a "molecular ruler" determines length by measurement against a physical structure in the biosynthetic complex. Escherichia coli O9a is a prototype for the biosynthesis of O polysaccharides by ATP-binding cassette transporter-dependent processes. The length of the O9a polysaccharide is determined by two proteins: an extension enzyme, WbdA, and a termination enzyme, WbdD. WbdD is known to self-oligomerize and also to interact with WbdA. Changing either enzyme's concentration can alter the polysaccharide length. We quantified the O9a polysaccharide length distribution and the enzyme concentration dependence in vivo, then made mathematical models to predict the polymer length distributions resulting from hypothetical length-regulation mechanisms. Our data show qualitative features that cannot be explained by either a molecular clock or a molecular ruler model. Therefore, we propose a "variable geometry" model, in which a postulated biosynthetic WbdA-WbdD complex assembles with variable stoichiometry dependent on relative enzyme concentration. Each stoichiometry produces polymers with a distinct, geometrically determined, modal length. This model reproduces the enzyme concentration dependence and modality of the observed polysaccharide length distributions. Our work highlights limitations of previous models and provides new insight into the mechanisms of length control in polysaccharide biosynthesis.

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Domain interactions control complex formation and polymerase specificity in the biosynthesis of the Escherichia coli O9a antigen.

Project description:The Escherichia coli O9a O-polysaccharide (O-PS) is a prototype for bacterial glycan synthesis and export by an ATP-binding cassette transporter-dependent pathway. The O9a O-PS possesses a tetrasaccharide repeat unit comprising two α-(1→2)- and two α-(1→3)-linked mannose residues and is extended on a polyisoprenoid lipid carrier by the action of a polymerase (WbdA) containing two glycosyltransferase active sites. The N-terminal domain of WbdA possesses α-(1→2)-mannosyltransferase activity, and we demonstrate in this study that the C-terminal domain is an α-(1→3)-mannosyltransferase. Previous studies established that the size of the O9a polysaccharide is determined by the chain-terminating dual kinase/methyltransferase (WbdD) that is tethered to the membrane and recruits WbdA into an active enzyme complex by protein-protein interactions. Here, we used bacterial two-hybrid analysis to identify a surface-exposed α-helix in the C-terminal mannosyltransferase domain of WbdA as the site of interaction with WbdD. However, the C-terminal domain was unable to interact with WbdD in the absence of its N-terminal partner. Through deletion analysis, we demonstrated that the α-(1→2)-mannosyltransferase activity of the N-terminal domain is regulated by the activity of the C-terminal α-(1→3)-mannosyltransferase. In mutants where the C-terminal catalytic site was deleted but the WbdD-interaction site remained, the N-terminal mannosyltransferase became an unrestricted polymerase, creating a novel polymer comprising only α-(1→2)-linked mannose residues. The WbdD protein therefore orchestrates critical localization and coordination of activities involved in chain extension and termination. Complex domain interactions are needed to position the polymerase components appropriately for assembly into a functional complex located at the cytoplasmic membrane.

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Project description:The O antigen is a polymer with a repeated unit. The chain length in most Escherichia coli strains has a modal value of 10 to 18 O units, but other strains have higher or lower modal values. wzz (cld/rol) mutants have a random chain length distribution, showing that the modal distribution is determined by the Wzz protein. Cloned wzz genes from E. coli strains with short (7 to 16), intermediate (10 to 18), and long (16 to 25) modal chain lengths were transferred to a model system, and their effects on O111 antigen were studied. The O111 chain length closely resembled that of the parent strains. We present data based on the construction of chimeric wzz genes and site-directed mutagenesis of the wzz gene to show that the modal value of O-antigen chain length of E. coli O1, O2, O7, and O157 strains can be changed by specific amino acid substitutions in wzz. It is concluded that the O-antigen chain length heterogeneity in E. coli strains is the result of amino acid sequence variation of the Wzz protein.

| S-EPMC107218 | biostudies-literature

Production of medium chain length fatty alcohols from glucose in Escherichia coli.

Project description:Metabolic engineering offers the opportunity to produce a wide range of commodity chemicals that are currently derived from petroleum or other non-renewable resources. Microbial synthesis of fatty alcohols is an attractive process because it can control the distribution of chain lengths and utilize low cost fermentation substrates. Specifically, primary alcohols with chain lengths of 12 to 14 carbons have many uses in the production of detergents, surfactants, and personal care products. The current challenge is to produce these compounds at titers and yields that would make them economically competitive. Here, we demonstrate a metabolic engineering strategy for producing fatty alcohols from glucose. To produce a high level of 1-dodecanol and 1-tetradecanol, an acyl-ACP thioesterase (BTE), an acyl-CoA ligase (FadD), and an acyl-CoA/aldehyde reductase (MAACR) were overexpressed in an engineered strain of Escherichia coli. Yields were improved by balancing expression levels of each gene, using a fed-batch cultivation strategy, and adding a solvent to the culture for extracting the product from cells. Using these strategies, a titer of over 1.6 g/L fatty alcohol with a yield of over 0.13 g fatty alcohol/g carbon source was achieved. These are the highest reported yield of fatty alcohols produced from glucose in E. coli.

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Substrate recognition by a carbohydrate-binding module in the prototypical ABC transporter for lipopolysaccharide O-antigen from <i>Escherichia coli</i> O9a.

Project description:Escherichia coli serotype O9a provides a model for export of lipopolysaccharide (LPS) O-antigen polysaccharide (O-PS) via ABC transporters. In O9a biosynthesis, a chain-terminator enzyme, WbdD, caps the nonreducing end of the glycan with a methylphosphate moiety and thereby establishes chain-length distribution. A carbohydrate-binding module (CBM) in the ABC transporter recognizes terminated glycans, ensuring that only mature O-PS is exported and incorporated into LPS. Here, we addressed two questions arising from this model. Are both residues in the binary terminator necessary for termination and export? And is a terminal methylphosphate moiety sufficient for export of heterologous glycans? To answer the first question, we uncoupled WbdD kinase and methyltransferase activities. WbdD mutants revealed that although the kinase activity is solely responsible for chain-length regulation, both activities are essential for CBM recognition and export. Consistent with this observation, a saturation transfer difference NMR experiment revealed a direct interaction between the CBM and the terminal methyl group. To determine whether methylphosphate is the sole determinant of substrate recognition by the CBM, we exploited Klebsiella pneumoniae O7, whose O-PS repeat-unit structure differs from O9a, but, as shown here, offers the second confirmed example of a terminal methylphosphate serving in substrate recognition. In vitro and in vivo experiments indicated that each CBM can bind the O-PS only with the native repeat unit, revealing that methylphosphate is essential but not sufficient for substrate recognition and export. Our findings provide important new insight into the structural determinants in a prototypical quality control system for glycan assembly and export.

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Molecular analysis of the O-antigen gene cluster of Escherichia coli O86:B7 and characterization of the chain length determinant gene (wzz).

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Identification of pseudouridine methyltransferase in Escherichia coli.

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| S-EPMC6287193 | biostudies-literature

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