Dataset Information

Conformational plasticity of the essential membrane-associated mannosyltransferase PimA from mycobacteria.

ABSTRACT: Phosphatidyl-myo-inositol mannosyltransferase A (PimA) is an essential glycosyltransferase (GT) that initiates the biosynthetic pathway of phosphatidyl-myo-inositol mannosides, lipomannan, and lipoarabinomannan, which are key glycolipids/lipoglycans of the mycobacterial cell envelope. PimA belongs to a large family of peripheral membrane-associated GTs for which the understanding of the molecular mechanism and conformational changes that govern substrate/membrane recognition and catalysis remains a major challenge. Here we used single molecule force spectroscopy techniques to study the mechanical and conformational properties of PimA. In our studies, we engineered a polyprotein containing PimA flanked by four copies of the well characterized I27 protein, which provides an unambiguous mechanical fingerprint. We found that PimA exhibits weak mechanical stability albeit displaying ?-sheet topology expected to unfold at much higher forces. Notably, PimA unfolds following heterogeneous multiple step mechanical unfolding pathways at low force akin to molten globule states. Interestingly, the ab initio low resolution envelopes obtained from small angle x-ray scattering of the unliganded PimA and the PimA·GDP complexed forms clearly demonstrate that not only the "open" and "closed" conformations of the GT-B enzyme are largely present in solution, but in addition, PimA experiences remarkable flexibility that undoubtedly corresponds to the N-terminal "Rossmann fold" domain, which has been proved to participate in protein-membrane interactions. Based on these results and on our previous experimental data, we propose a model wherein the conformational transitions are important for the mannosyltransferase to interact with the donor and acceptor substrates/membrane.

SUBMITTER: Giganti D

PROVIDER: S-EPMC3795279 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Conformational plasticity of the essential membrane-associated mannosyltransferase PimA from mycobacteria.

Giganti David D Alegre-Cebollada Jorge J Urresti Saioa S Albesa-Jové David D Rodrigo-Unzueta Ane A Comino Natalia N Kachala Michael M López-Fernández Sonia S Svergun Dmitri I DI Fernández Julio M JM Guerin Marcelo E ME

The Journal of biological chemistry 20130820 41

Phosphatidyl-myo-inositol mannosyltransferase A (PimA) is an essential glycosyltransferase (GT) that initiates the biosynthetic pathway of phosphatidyl-myo-inositol mannosides, lipomannan, and lipoarabinomannan, which are key glycolipids/lipoglycans of the mycobacterial cell envelope. PimA belongs to a large family of peripheral membrane-associated GTs for which the understanding of the molecular mechanism and conformational changes that govern substrate/membrane recognition and catalysis remain ...[more]

PMID: 23963451

Similar Datasets

Project description:UnlabelledIron acquisition at the outer membrane (OM) of Gram-negative bacteria is powered by the proton motive force (PMF) of the cytoplasmic membrane (CM), harnessed by the CM-embedded complex of ExbB, ExbD, and TonB. Its stoichiometry, ensemble structural features, and mechanism of action are unknown. By panning combinatorial phage libraries, periplasmic regions of dimerization between ExbD and TonB were predicted. Using overexpression of full-length His6-tagged exbB-exbD and S-tagged tonB, we purified detergent-solubilized complexes of ExbB-ExbD-TonB from Escherichia coli. Protein-detergent complexes of ∼230 kDa with a hydrodynamic radius of ∼6.0 nm were similar to previously purified ExbB₄-ExbD₂ complexes. Significantly, they differed in electronegativity by native agarose gel electrophoresis. The stoichiometry was determined to be ExbB₄-ExbD₁-TonB₁. Single-particle electron microscopy agrees with this stoichiometry. Two-dimensional averaging supported the phage display predictions, showing two forms of ExbD-TonB periplasmic heterodimerization: extensive and distal. Three-dimensional (3D) particle classification showed three representative conformations of ExbB₄-ExbD₁-TonB₁. Based on our structural data, we propose a model in which ExbD shuttles a proton across the CM via an ExbB interprotein rearrangement. Proton translocation would be coupled to ExbD-mediated collapse of extended TonB in complex with ligand-loaded receptors in the OM, followed by repositioning of TonB through extensive dimerization with ExbD. Here we present the first report for purification of the ExbB-ExbD-TonB complex, molar ratios within the complex (4:1:1), and structural biology that provides insights into 3D organization.ImportanceReceptors in the OM of Gram-negative bacteria allow entry of iron-bound siderophores that are necessary for pathogenicity. Numerous iron-acquisition strategies rely upon a ubiquitous and unique protein for energization: TonB. Complexed with ExbB and ExbD, the Ton system links the PMF to OM transport. Blocking iron uptake by targeting a vital nanomachine holds promise in therapeutics. Despite much research, the stoichiometry, structural arrangement, and molecular mechanism of the CM-embedded ExbB-ExbD-TonB complex remain unreported. Here we demonstrate in vitro evidence of ExbB₄-ExbD₁-TonB₁ complexes. Using 3D EM, we reconstructed the complex in three conformational states that show variable ExbD-TonB heterodimerization. Our structural observations form the basis of a model for TonB-mediated iron acquisition.

Project description:Mycobacteria possess different type VII secretion (T7S) systems to secrete proteins across their unusual cell envelope. One of these systems, ESX-5, is only present in slow-growing mycobacteria and responsible for the secretion of multiple substrates. However, the role of ESX-5 substrates in growth and/or virulence is largely unknown. In this study, we show that esx-5 is essential for growth of both Mycobacterium marinum and Mycobacterium bovis. Remarkably, this essentiality can be rescued by increasing the permeability of the outer membrane, either by altering its lipid composition or by the introduction of the heterologous porin MspA. Mutagenesis of the first nucleotide-binding domain of the membrane ATPase EccC5 prevented both ESX-5-dependent secretion and bacterial growth, but did not affect ESX-5 complex assembly. This suggests that the rescuing effect is not due to pores formed by the ESX-5 membrane complex, but caused by ESX-5 activity. Subsequent proteomic analysis to identify crucial ESX-5 substrates confirmed that all detectable PE and PPE proteins in the cell surface and cell envelope fractions were routed through ESX-5. Additionally, saturated transposon-directed insertion-site sequencing (TraDIS) was applied to both wild-type M. marinum cells and cells expressing mspA to identify genes that are not essential anymore in the presence of MspA. This analysis confirmed the importance of esx-5, but we could not identify essential ESX-5 substrates, indicating that multiple of these substrates are together responsible for the essentiality. Finally, examination of phenotypes on defined carbon sources revealed that an esx-5 mutant is strongly impaired in the uptake and utilization of hydrophobic carbon sources. Based on these data, we propose a model in which the ESX-5 system is responsible for the transport of cell envelope proteins that are required for nutrient uptake. These proteins might in this way compensate for the lack of MspA-like porins in slow-growing mycobacteria.

Dataset Information

Conformational plasticity of the essential membrane-associated mannosyltransferase PimA from mycobacteria.

Publications

Conformational plasticity of the essential membrane-associated mannosyltransferase PimA from mycobacteria.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets