The mannose transporter complex: an open door for the macromolecular invasion of bacteria

Genome and proteome analyses show the gaseous alkane degrader Desulfosarcina sp. strain BuS5 as an extreme metabolic specialist

The metabolic potential of the sulfate-reducing bacterium Desulfosarcina sp. strain BuS5, currently the only pure culture able to oxidize the volatile alkanes propane and butane without oxygen, was investigated via genomics, proteomics and physiology assays. Complete genome sequencing revealed that strain BuS5 encodes a single alkyl-succinate synthase, an enzyme which apparently initiates oxidation of both propane and butane. The formed alkyl-succinates are oxidized to CO₂ via beta oxidation and the oxidative Wood-Ljungdahl pathways as shown by proteogenomics analyses. Strain BuS5 conserves energy via the canonical sulfate reduction pathway and electron bifurcation. An ability to utilize long-chain fatty acids, mannose and oligopeptides, suggested by automated annotation pipelines, was not supported by physiology assays and in-depth analyses of the corresponding genetic systems. Consistently, comparative genomics revealed a streamlined BuS5 genome with a remarkable paucity of catabolic modules. These results establish strain BuS5 as an exceptional metabolic specialist, able to grow only with propane and butane, for which we propose the name Desulfosarcina aeriophaga BuS5. This highly restrictive lifestyle, most likely the result of habitat-driven evolutionary gene loss, may provide D. aeriophaga BuS5 a competitive edge in sediments impacted by natural gas seeps. Etymology: Desulfosarcina aeriophaga, aério (Greek): gas; phágos (Greek): eater; D. aeriophaga: a gas eating or gas feeding Desulfosarcina.

Pediocin-Like Antimicrobial Peptides of Bacteria

Bacteriocins are bacterial antimicrobial peptides that, unlike classical peptide antibiotics, are products of ribosomal synthesis and usually have a narrow spectrum of antibacterial activity against species closely related to the producers. Pediocin-like bacteriocins (PLBs) belong to the class IIa of the bacteriocins of Gram-positive bacteria. PLBs possess high activity against pathogenic bacteria from Listeria and Enterococcus genera. Molecular target for PLBs is a membrane protein complex - bacterial mannose-phosphotransferase. PLBs can be synthesized by components of symbiotic microflora and participate in the maintenance of homeostasis in various compartments of the digestive tract and on the surface of epithelial tissues contacting the external environment. PLBs could give a rise to a new group of antibiotics of narrow spectrum of activity.

The importance of the glycosylation of antimicrobial peptides: natural and synthetic approaches

Glycosylation is one of the most prevalent post-translational modifications of a protein, with a defining impact on its structure and function. Many of the proteins involved in the innate or adaptive immune response, including cytokines, chemokines, and antimicrobial peptides (AMPs), are glycosylated, contributing to their myriad activities. The current availability of synthetic coupling and glycoengineering technology makes it possible to customise the most beneficial glycan modifications for improved AMP stability, microbicidal potency, pathogen specificity, tissue or cell targeting, and immunomodulation.

The Bacterial Phosphotransferase System: New Frontiers 50 Years after Its Discovery

In 1964, Kundig, Ghosh and Roseman reported the discovery of the phosphoenolpyruvate:sugar phosphotransferase system (PTS), which they subsequently proposed might catalyze sugar transport as well as sugar phosphorylation. What we have learned in the 50 years since its discovery is that, in addition to these primary functions, the PTS serves as a complex protein kinase system that regulates a wide variety of transport, metabolic and mutagenic processes as well as the expression of numerous genes. Recent operon- and genome-sequencing projects have revealed novel PTS protein-encoding genes, many of which have yet to be functionally defined. The current picture of the PTS is that of a complex system with ramifications in all aspects of cellular physiology. Moreover, its mosaic evolutionary history is unusual and intriguing. The PTS can be considered to serve many prokaryotes in capacities of communication and coordination, as do the nervous systems of animals.

Class IIa bacteriocins: diversity and new developments

Class IIa bacteriocins are heat-stable, unmodified peptides with a conserved amino acids sequence YGNGV on their N-terminal domains, and have received much attention due to their generally recognized as safe (GRAS) status, their high biological activity, and their excellent heat stability. They are promising and attractive agents that could function as biopreservatives in the food industry. This review summarizes the new developments in the area of class IIa bacteriocins and aims to provide uptodate information that can be used in designing future research.

An extracellular loop of the mannose phosphotransferase system component IIC is responsible for specific targeting by class IIa bacteriocins

Class IIa bacteriocins target a phylogenetically defined subgroup of mannose-phosphotransferase systems (man-PTS) on sensitive cells. By the use of man-PTS genes of the sensitive Listeria monocytogenes (mpt) and the nonsensitive Lactococcus lactis (ptn) species to rationally design a series of man-PTS chimeras and site-directed mutations, we identified an extracellular loop of the membrane-located protein MptC that was responsible for specific target recognition by the class IIa bacteriocins.

Localization of the substrate-binding site in the homodimeric mannitol transporter, EIImtl, of Escherichia coli

The mannitol transporter from Escherichia coli, EII(mtl), belongs to a class of membrane proteins coupling the transport of substrates with their chemical modification. EII(mtl) is functional as a homodimer, and it harbors one high affinity mannitol-binding site in the membrane-embedded C domain (IIC(mtl)). To localize this binding site, 19 single Trp-containing mutants of EII(mtl) were biosynthetically labeled with 5-fluorotryptophan (5-FTrp) and mixed with azi-mannitol, a substrate analog acting as a Förster resonance energy transfer (FRET) acceptor. Typically, for mutants showing FRET, only one 5-FTrp was involved, whereas the 5-FTrp from the other monomer was too distant. This proves that the mannitol-binding site is asymmetrically positioned in dimeric IIC(mtl). Combined with the available two-dimensional projection maps of IIC(mtl), it is concluded that a second resting binding site is present in this transporter. Active transport of mannitol only takes place when EII(mtl) becomes phosphorylated at Cys(384) in the cytoplasmic B domain. Stably phosphorylated EII(mtl) mutants were constructed, and FRET experiments showed that the position of mannitol in IIC(mtl) remains the same. We conclude that during the transport cycle, the phosphorylated B domain has to move to the mannitol-binding site, located in the middle of the membrane, to phosphorylate mannitol.

Expression, purification, crystallization and preliminary X-ray analysis of the EIICGlc domain of the Escherichia coli glucose transporter

The glucose-import system of Escherichia coli consists of a hydrophilic EIIA(Glc) subunit and a transmembrane EIICB(Glc) subunit. EIICB(Glc) (UniProt P69786) contains two domains: the transmembrane EIIC(Glc) domain (40.6 kDa) and the cytoplasmic EIIB(Glc) domain (8.0 kDa), which are fused by a linker that is strongly conserved among its orthologues. The EIICB(Glc) subunit can be split within this motif by trypsin. Here, the crystallization of the tryptic EIIC(Glc) domain is described. A complete data set was collected to 4.5 A resolution at 100 K.

Involvement of the mannose phosphotransferase system of Lactobacillus plantarum WCFS1 in peroxide stress tolerance

A Lactobacillus plantarum strain with a deletion in the gene rpoN, encoding the alternative sigma factor 54 (sigma(54)), displayed a 100-fold-higher sensitivity to peroxide than its parental strain. This feature could be due to sigma(54)-dependent regulation of genes involved in the peroxide stress response. However, transcriptome analyses of the wild type and the mutant strain during peroxide exposure did not support such a role for sigma(54). Subsequent experiments revealed that the impaired expression of the mannose phosphotransferase system (PTS) operon in the rpoN mutant caused the observed increased peroxide sensitivity.

Contact-dependent growth inhibition requires the essential outer membrane protein BamA (YaeT) as the receptor and the inner membrane transport protein AcrB

Contact-dependent growth inhibition (CDI) is a phenomenon by which bacterial cell growth is regulated by direct cell-to-cell contact via the CdiA/CdiB two-partner secretion system. Characterization of mutants resistant to CDI allowed us to identify BamA (YaeT) as the outer membrane receptor for CDI and AcrB as a potential downstream target. Notably, both BamA and AcrB are part of distinct multi-component machines. The Bam machine assembles outer membrane beta-barrel proteins into the outer membrane and the Acr machine exports small molecules into the extracellular milieu. We discovered that a mutation that reduces expression of BamA decreased binding of CDI+ inhibitor cells, measured by flow cytometry with fluorescently labelled bacteria. In addition, alpha-BamA antibodies, which recognized extracellular epitopes of BamA based on immunofluorescence, specifically blocked inhibitor-target cells binding and CDI. A second class of CDI-resistant mutants identified carried null mutations in the acrB gene. AcrB is an inner membrane component of a multidrug efflux pump that normally forms a cell envelope-spanning complex with the membrane fusion protein AcrA and the outer membrane protein TolC. Strikingly, the requirement for the BamA and AcrB proteins in CDI is independent of their multi-component machines, and thus their role in the CDI pathway may reflect novel, import-related functions.

Ins and outs of glucose transport systems in eubacteria

Glucose is the classical carbon source that is used to investigate the transport, metabolism, and regulation of nutrients in bacteria. Many physiological phenomena like nutrient limitation, stress responses, production of antibiotics, and differentiation are inextricably linked to nutrition. Over the years glucose transport systems have been characterized at the molecular level in more than 20 bacterial species. This review aims to provide an overview of glucose uptake systems found in the eubacterial kingdom. In addition, it will highlight the diverse and sophisticated regulatory features of glucose transport systems.

Molecular dynamics simulation study of interaction between a class IIa bacteriocin and its immunity protein

Molecular dynamics (MD) simulations of carnobacteriocin B2 (CbnB2), a structurally well-characterized class IIa bacteriocin, and its immunity protein (ImB2) in lipid bilayer environment have been conducted to explore the interaction between them. Six 30-ns simulations were conducted in DPPC or POPG bilayer systems. In these simulations, ImB2 was placed in the aqueous layer with different orientations facing CbnB2 to sample all the faces of ImB2. The MD results indicate that (i) while CbnB2 remained embedded in the bilayer, it tends to move toward the interface, and (ii) the presence of CbnB2 in the DPPC bilayer attracts ImB2 toward the bilayer. In one of the orientations in DPPC bilayer system (simulation 1), ImB2 penetrates the bilayer and interacts with CbnB2 by ion-pair interaction. At several instances toward the later half of the simulation (15-30 ns), ImB2 and CbnB2 were found to form salt-bridge between Arg95 of ImB2 and Glu24 of CbnB2. Simulation in POPG bilayer displayed strong interaction between the positively charged ImB2 and the negatively charged polar head groups of the POPG molecules at the lipid-water interface. However, ImB2 was not able to penetrate the bilayer thereby preventing any interaction between ImB2 and CbnB2.