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Biomolecules Apr 2020Spirochetes can be distinguished from other flagellated bacteria by their long, thin, spiral (or wavy) cell bodies and endoflagella that reside within the periplasmic... (Review)
Review
Spirochetes can be distinguished from other flagellated bacteria by their long, thin, spiral (or wavy) cell bodies and endoflagella that reside within the periplasmic space, designated as periplasmic flagella (PFs). Some members of the spirochetes are pathogenic, including the causative agents of syphilis, Lyme disease, swine dysentery, and leptospirosis. Furthermore, their unique morphologies have attracted attention of structural biologists; however, the underlying physics of viscoelasticity-dependent spirochetal motility is a longstanding mystery. Elucidating the molecular basis of spirochetal invasion and interaction with hosts, resulting in the appearance of symptoms or the generation of asymptomatic reservoirs, will lead to a deeper understanding of host-pathogen relationships and the development of antimicrobials. Moreover, the mechanism of propulsion in fluids or on surfaces by the rotation of PFs within the narrow periplasmic space could be a designing base for an autonomously driving micro-robot with high efficiency. This review describes diverse morphology and motility observed among the spirochetes and further summarizes the current knowledge on their mechanisms and relations to pathogenicity, mainly from the standpoint of experimental biophysics.
Topics: Flagella; Movement; Periplasm; Spirochaetales
PubMed: 32260454
DOI: 10.3390/biom10040550 -
Current Opinion in Structural Biology Apr 2021The Ton complex is a molecular motor that uses the proton gradient at the inner membrane of Gram-negative bacteria to apply forces on outer membrane proteins, allowing... (Review)
Review
The Ton complex is a molecular motor that uses the proton gradient at the inner membrane of Gram-negative bacteria to apply forces on outer membrane proteins, allowing active transport of nutrients into the periplasmic space. For decades, contradictory data has been reported on the structure and stoichiometry of the Ton complex. However, recent reports strongly support a subunit stoichiometry of 5:2 for the ExbB-ExbD subcomplex. In this review, we summarize the recent discoveries of the structures and proposed mechanisms of the Ton system, as well as similar protein motor complexes in Gram-negative bacteria.
Topics: Bacterial Proteins; Escherichia coli; Escherichia coli Proteins; Gram-Negative Bacteria; Membrane Proteins; Periplasm
PubMed: 33157479
DOI: 10.1016/j.sbi.2020.09.014 -
Trends in Biochemical Sciences Oct 2016Outer membrane proteins (OMPs) play a central role in the integrity of the outer membrane of Gram-negative bacteria. Unfolded OMPs (uOMPs) transit across the periplasm,... (Review)
Review
Outer membrane proteins (OMPs) play a central role in the integrity of the outer membrane of Gram-negative bacteria. Unfolded OMPs (uOMPs) transit across the periplasm, and subsequent folding and assembly are crucial for biogenesis. Chaperones and the essential β-barrel assembly machinery (BAM) complex facilitate these processes. In vitro studies suggest that some chaperones sequester uOMPs in internal cavities during their periplasmic transit to prevent deleterious aggregation. Upon reaching the outer membrane, the BAM complex acts catalytically to accelerate uOMP folding. Complementary in vivo experiments have revealed the localization and activity of the BAM complex in living cells. Completing an understanding of OMP biogenesis will require a holistic view of the interplay among the individual components discussed here.
Topics: Bacterial Outer Membrane Proteins; Binding Sites; Escherichia coli; Escherichia coli Proteins; Gene Expression; Molecular Chaperones; Molecular Dynamics Simulation; Periplasm; Protein Binding; Protein Conformation, beta-Strand; Protein Folding; Protein Interaction Domains and Motifs; Protein Transport; Protein Unfolding; Thermodynamics
PubMed: 27450425
DOI: 10.1016/j.tibs.2016.06.005 -
Microbiology Spectrum Jul 2019Periplasmic flagella are complex nanomachines responsible for distinctive morphology and motility of spirochetes. Although bacterial flagella have been extensively... (Review)
Review
Periplasmic flagella are complex nanomachines responsible for distinctive morphology and motility of spirochetes. Although bacterial flagella have been extensively studied for several decades in the model systems and , our understanding of periplasmic flagella in many disease-causing spirochetes remains incomplete. Recent advances, including molecular genetics, biochemistry, structural biology, and cryo-electron tomography, have greatly increased our understanding of structure and function of periplasmic flagella. In this chapter, we summarize some of the recent findings that provide new insights into the structure, assembly, and function of periplasmic flagella.
Topics: Bacterial Proteins; Borrelia burgdorferi; Escherichia coli; Flagella; Periplasm; Salmonella enterica
PubMed: 31373267
DOI: 10.1128/microbiolspec.PSIB-0030-2019 -
Applied and Environmental Microbiology Apr 2021Extracellular electron transfer (EET) is an important biological process in microbial physiology as found in dissimilatory metal oxidation/reduction and interspecies... (Review)
Review
Extracellular electron transfer (EET) is an important biological process in microbial physiology as found in dissimilatory metal oxidation/reduction and interspecies electron transfer in syntrophy in natural environments. EET also plays a critical role in microorganisms relevant to environmental biotechnology in metal-contaminated areas, metal corrosion, bioelectrochemical systems, and anaerobic digesters. species exist in a diversity of natural and artificial environments. One of the outstanding features of species is the capability of direct EET with solid electron donors and acceptors, including metals, electrodes, and other cells. Therefore, species are pivotal in environmental biogeochemical cycles and biotechnology applications. , a representative species, has been studied for direct EET as a model microorganism. employs electrically conductive pili (e-pili) and -type cytochromes for the direct EET. The biological function and electronics applications of the e-pili have been reviewed recently, and this review focuses on the cytochromes. species have an unusually large number of cytochromes encoded in their genomes. Unlike most other microorganisms, species localize multiple cytochromes in each subcellular fraction, outer membrane, periplasm, and inner membrane, as well as in the extracellular space, and differentially utilize these cytochromes for EET with various electron donors and acceptors. Some of the cytochromes are functionally redundant. Thus, the EET in is complicated. coordinates the cytochromes with other cellular components in the elaborate EET system to flourish in the environment.
Topics: Bacterial Outer Membrane; Cytochromes; Electron Transport; Geobacter; Intracellular Membranes; Periplasm
PubMed: 33741623
DOI: 10.1128/AEM.03109-20 -
Nature May 2021Mycobacterium tuberculosis is the cause of one of the most important infectious diseases in humans, which leads to 1.4 million deaths every year. Specialized protein...
Mycobacterium tuberculosis is the cause of one of the most important infectious diseases in humans, which leads to 1.4 million deaths every year. Specialized protein transport systems-known as type VII secretion systems (T7SSs)-are central to the virulence of this pathogen, and are also crucial for nutrient and metabolite transport across the mycobacterial cell envelope. Here we present the structure of an intact T7SS inner-membrane complex of M. tuberculosis. We show how the 2.32-MDa ESX-5 assembly, which contains 165 transmembrane helices, is restructured and stabilized as a trimer of dimers by the MycP protease. A trimer of MycP caps a central periplasmic dome-like chamber that is formed by three EccB dimers, with the proteolytic sites of MycP facing towards the cavity. This chamber suggests a central secretion and processing conduit. Complexes without MycP show disruption of the EccB periplasmic assembly and increased flexibility, which highlights the importance of MycP for complex integrity. Beneath the EccB-MycP chamber, dimers of the EccC ATPase assemble into three bundles of four transmembrane helices each, which together seal the potential central secretion channel. Individual cytoplasmic EccC domains adopt two distinctive conformations that probably reflect different secretion states. Our work suggests a previously undescribed mechanism of protein transport and provides a structural scaffold to aid in the development of drugs against this major human pathogen.
Topics: Cryoelectron Microscopy; Cytosol; Models, Molecular; Mycobacterium tuberculosis; Periplasm; Protein Domains; Protein Multimerization; Protein Stability; Tuberculosis; Type VII Secretion Systems
PubMed: 33981042
DOI: 10.1038/s41586-021-03517-z -
Current Topics in Microbiology and... 2018The outer membrane (OM) of Treponema pallidum, the uncultivatable agent of venereal syphilis, has long been the subject of misconceptions and controversy. Decades ago,... (Review)
Review
The outer membrane (OM) of Treponema pallidum, the uncultivatable agent of venereal syphilis, has long been the subject of misconceptions and controversy. Decades ago, researchers postulated that T. pallidum's poor surface antigenicity is the basis for its ability to cause persistent infection, but they mistakenly attributed this enigmatic property to the presence of a protective outer coat of serum proteins and mucopolysaccharides. Subsequent studies revealed that the OM is the barrier to antibody binding, that it contains a paucity of integral membrane proteins, and that the preponderance of the spirochete's immunogenic lipoproteins is periplasmic. Since the advent of recombinant DNA technology, the fragility of the OM, its low protein content, and the lack of sequence relatedness between T. pallidum and Gram-negative outer membrane proteins (OMPs) have complicated efforts to characterize molecules residing at the host-pathogen interface. We have overcome these hurdles using the genomic sequence in concert with computational tools to identify proteins predicted to form β-barrels, the hallmark conformation of OMPs in double-membrane organisms and evolutionarily related eukaryotic organelles. We also have employed diverse methodologies to confirm that some candidate OMPs do, in fact, form amphiphilic β-barrels and are surface-exposed in T. pallidum. These studies have led to a structural homology model for BamA and established the bipartite topology of the T. pallidum repeat (Tpr) family of proteins. Recent bioinformatics has identified several structural orthologs for well-characterized Gram-negative OMPs, suggesting that the T. pallidum OMP repertoire is more Gram-negative-like than previously supposed. Lipoprotein adhesins and proteases on the spirochete surface also may contribute to disease pathogenesis and protective immunity.
Topics: Bacterial Outer Membrane Proteins; Humans; Periplasm; Syphilis; Treponema pallidum
PubMed: 28849315
DOI: 10.1007/82_2017_44 -
MBio Apr 2023Over the billions of years that bacteria have been around, they have evolved several sophisticated protein secretion nanomachines to deliver toxins, hydrolytic enzymes,... (Review)
Review
Over the billions of years that bacteria have been around, they have evolved several sophisticated protein secretion nanomachines to deliver toxins, hydrolytic enzymes, and effector proteins into their environments. Of these, the type II secretion system (T2SS) is used by Gram-negative bacteria to export a wide range of folded proteins from the periplasm across the outer membrane. Recent findings have demonstrated that components of the T2SS are localized in mitochondria of some eukaryotic lineages, and their behavior is consistent with the presence of a mitochondrial T2SS-derived system (miT2SS). This review focuses on recent advances in the field and discusses open questions concerning the function and evolution of miT2SSs.
Topics: Type II Secretion Systems; Bacterial Proteins; Gram-Negative Bacteria; Periplasm; Bacterial Secretion Systems
PubMed: 36971557
DOI: 10.1128/mbio.03145-22 -
Trends in Biochemical Sciences Nov 2016Biochemical processes take place in heterogeneous and highly volume-occupied or crowded environments that can considerably influence the reactivity and distribution of... (Review)
Review
Biochemical processes take place in heterogeneous and highly volume-occupied or crowded environments that can considerably influence the reactivity and distribution of participating macromolecules. We summarize here the thermodynamic consequences of excluded-volume and long-range nonspecific intermolecular interactions for macromolecular reactions in volume-occupied media. In addition, we summarize and compare the information content of studies of crowding in vitro and in vivo. We emphasize the importance of characterizing the behavior not only of labeled tracer macromolecules but also the composition and behavior of unlabeled macromolecules in the immediate vicinity of the tracer. Finally, we propose strategies for extending quantitative analyses of crowding in simple model systems to increasingly complex media up to and including intact cells.
Topics: Bacterial Proteins; Cell Compartmentation; Cell Membrane; DNA, Bacterial; Escherichia coli; Kinetics; Organelles; Periplasm; RNA, Bacterial; Thermodynamics
PubMed: 27669651
DOI: 10.1016/j.tibs.2016.08.013 -
Science Advances Jul 2023Semiconductor-based biointerfaces are typically established either on the surface of the plasma membrane or within the cytoplasm. In Gram-negative bacteria, the...
Semiconductor-based biointerfaces are typically established either on the surface of the plasma membrane or within the cytoplasm. In Gram-negative bacteria, the periplasmic space, characterized by its confinement and the presence of numerous enzymes and peptidoglycans, offers additional opportunities for biomineralization, allowing for nongenetic modulation interfaces. We demonstrate semiconductor nanocluster precipitation containing single- and multiple-metal elements within the periplasm, as observed through various electron- and x-ray-based imaging techniques. The periplasmic semiconductors are metastable and display defect-dominant fluorescent properties. Unexpectedly, the defect-rich (i.e., the low-grade) semiconductor nanoclusters produced in situ can still increase adenosine triphosphate levels and malate production when coupled with photosensitization. We expand the sustainability levels of the biohybrid system to include reducing heavy metals at the primary level, building living bioreactors at the secondary level, and creating semi-artificial photosynthesis at the tertiary level. The biomineralization-enabled periplasmic biohybrids have the potential to serve as defect-tolerant platforms for diverse sustainable applications.
Topics: Periplasm; Biomineralization; Cell Membrane; Cytoplasm; Photosynthesis
PubMed: 37478187
DOI: 10.1126/sciadv.adg5858