Bacterial Secreted Proteins: Secretory Mechanisms and Role in Pathogenesis | Book
Caister Academic Press
Karl Wooldridge Centre for Biomolecular Sciences, University of Nottingham, UK
April 2009 Available now!
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Secreted proteins are particularly important in bacterial pathogenesis. These proteins have a range of biological functions ranging from host cell toxicity to more subtle alterations of the host cell for the benefit of the invader. The importance of protein secretion to bacterial pathogens is exemplified by the array of mechanisms that have evolved for this purpose.
This extensive publication on bacterial secreted proteins, the secretory systems of bacteria and the vital role of secreted proteins in bacterial pathogenesis will be of immense value to all microbiologists, molecular biologists, public health scientists and researchers engaged in the study of pathogenesis, drug design and vaccine development. A skillful selection of topics and a panel of acknowledged experts as authors have ensured that this volume will become an important reference source for many years to come.
The book is divided into two sections. The first section describes the various protein secretion systems including mechanisms for secretion across the cytoplasmic membrane of Gram-negative and Gram-positive bacteria, specialized mechanisms for secretion across the Gram-negative outer membrane, systems for transport across both membranes of Gram-negative bacteria, protein secretion systems in Gram-positive bacteria, the secretion of surface fimbrae/pili and a chapter on the less well defined pathways. Section 2 describes the protein secretion mechanisms and secreted proteins of a number of important human, veterinary and plant pathogens and their role in the pathogenicity of these organisms. The pathogens covered have been selected on the basis that there is active research on protein secretion by these pathogens and they employ a diverse array of secreted proteins and protein secretion systems. Each chapter of the book can be read in isolation, particularly the chapters in section 2. The book constitutes a broad and in-depth description of the current knowledge of bacterial protein secretion and its role in pathogenesis. A recommended reference volume for all microbiology libraries.
"This well designed book will provide a clear understanding of how bacterial protein secretion occurs." from Doodys Book Review Service
"This collection of expert reviews provided the reader with a detailed insight into the exotic world of secreted proteins ... well referenced throughout with many chapters being especially up to date ... Dr Wooldridge is to be complimented on assembling such a knowledgeable group of lucid authors who review a rapidly advancing and complex field in an easy to read manner." from Expert Review of Anti-infective Therapy (August 2009)
"This timely collection of reviews ... is excellent coverage of the major transport and secretion systems in Escherichia coli, Salmonella enterica and many other Gram-negative bacteria. ... an extensive and valuable resource for protein secretion ... the volume is indubitably a worthy addition to the personal reference collection of every bacteriologist with an interest in host-pathogen interactions." from Microbiology Today (2009)
"This publication provides a broad and in-depth description of the current knowledge of bacterial protein secretion and its role in pathogenesis" from Food Science and Technology Abstracts (2010) 42(8)
"well designed book" (Doodys); "broad and in-depth" (Food Sci. Technol. Abs.); "timely ... extensive and valuable resource" (Microbiol. Today)
Section 1: Bacterial Protein Secretion Systems
The Sec Protein Secretion System
Koreaki Ito and Hiroyuki Mori
The majority of proteins destined for export across the cytoplasmic membrane or integration into the membrane are handled by the evolutionarily conserved Sec system. The Sec substrates have specific topogenic signals and are targeted to the membrane-embedded SecYEG translocon that serves as a polypeptide-conducting channel either co-translationally by SRP for lipid-phase integration or post-translationally by SecB for complete translocation. The plug helix of SecY that clogs the unused channel and the central constriction that seals around the translocating chain make the translocon function compatible with the permeability barrier of the membrane. The translocon also contains a lateral gate, through which it not only accepts a newly synthesized client protein but also allows its hydrophobic segment, if any, to partition into the lipid phase. The post-translational mode of translocation, characteristic of the bacterial systems, is driven by the SecA ATPase, which interacts with SecY and a preprotein and accordingly undergoes conformational transitions coupled with the ATPase cycles. While recent progress in structural analyses of these components is remarkable, real molecular understanding of their dynamic actions is left for future studies.
The Twin-Arginine Translocation Pathway
Sascha Panahandeh, Eva Holzapfel and Matthias Müller
The twin-arginine translocation (Tat) pathway is a protein transport system in bacteria, archaea and chloroplasts with the ability to export proteins in a fully folded conformation. Proteins are targeted to the Tat pathway by an N-terminal signal peptide containing an almost invariant twin-arginine sequence motif. Pretranslocational folding is necessitated by the incorporation of metallo-cofactors, assembly into oligomeric complexes, and presumably rapid folding kinetics. Many Tat systems comprise three functionally individual membrane proteins, termed TatA, TatB, and TatC, whereas especially Gram-positive bacteria possess minimal TatAC translocases, in which TatA functionally replaces TatB. TatC and TatB form a complex that is involved in recognition of Tat signal sequences and their insertion into the membrane. TatA mediates the actual translocation event, but it is unclear whether it does so by forming the pore-like structures that it displays when purified to homogeneity. Energy is derived from either component of the proton-motive force, ΔpH or ΔΨ, and is required only for late steps following signal sequence cleavage. Substrates that either lack the twin-arginine pair or are in a malfolded conformation in general are not translocated. The mechanisms by which non-functional substrates are rejected are not understood. For cofactor-containing substrates, proof-reading seems to depend on the activity of specific cytosolic chaperones.
Type I Bacterial Secretion Systems
Stefan Jenewein, I. Barry Holland and Lutz Schmitt
Bacteria have developed numerous systems to secrete proteins or DNA in order to modify their immediate surroundings or to obtain an advantage in a competitive and hostile environment. Since Gram-negative bacteria possess two membranes, the inner (cytoplasmic) membrane and the outer membrane, transport machines for protein secretion have the challenging task of circumventing two barriers to reach the exterior. Complex nanomachines like the Type II secretion systems, involving a two stage process with a periplasmic intermediate, have evolved for that purpose. However, a rather simple transport apparatus, the Type I secretion machinery, composed of only three proteins residing in the inner and outer membrane of Gram-negative bacteria achieve the same objective in a single step, with no periplasmic intermediate. The Type I secretion pathway although also present in Gram-positive bacteria, has been analysed in greatest detail in Gram-negative bacteria and this will be the primary focus of this chapter. Almost all Type I transport substrates are polypeptides, varying from the small Escherichia coli
peptide colicin V, (10 kDa) to the impressive size of the Pseudomonas fluorescens
cell adhesion protein LapA of 900 kDa. While these two examples reflect the range of the size of Type I transport substrates, the best characterized are the RTX toxins and the lipases. Note that the terms transport substrates or allocrites, the name we have coined to designate an unprocessed substrate for the ABC transporter, in contrast to the substrate ATP, which is hydrolyzed, will be used interchangeably in this chapter. Type I secretion is also apparently involved in export of non-proteinaceous substrates like cyclic β-glucans or polysaccharides, but definitive studies are lacking. Here, we shall only focus on the fundamental properties of the pathway whereby polypeptides are secreted to the extracellular medium via the Type I secretion mechanism.
The Type II Secretory System (T2SS) in Gram-negative Bacteria: A Molecular Nanomachine for Secretion of Sec and Tat-Dependent Extracellular Proteins
Gérard P.F. Michel and Romé Voulhoux
Gram-negative bacteria have evolved several secretory pathways to release proteins or toxic factors into their surrounding environment. Many virulence determinants, including extracellular toxins and proteases, are secreted by the type II secretion system (T2SS) which is widely conserved and common among γ-proteobacteria. Typical T2SSs are composed of 12 to 16 proteins termed Gsp (General secretion pathway) proteins. These components associate in a multiprotein complex that constitutes a large structure (the secreton) that spans the periplasm and is thought to connect inner and outer membranes. Exoproteins that use the T2SS are characterized by the presence of a leader peptide (or signal peptide) at their N terminus and are secreted in the extracellular medium by a two-step process involving a transient periplasmic intermediate. The T2SS is unique in its ability to promote secretion of large multimeric proteins that are folded in the periplasm. The system is also characterized by a species-specificity, which is mainly related to the GspC and GspD components, the gatekeepers. Although relatively little attention has been payed to the regulation of T2SSs, it was observed that expression of most of the genes encoding T2SS-dependent exoproteins is growth phase-dependent or strictly regulated by environmental signals. In Pseudomonas aeruginosa
, T2SS assembly and most of the T2SS-dependent exoproteins are regulated via quorum sensing, a mechanism that senses the density of a surrounding bacterial population. Besides typical T2SSs, some secretory systems are found which contain all the T2SS components but in a different genetic organization. Some incomplete systems have also been described which contain genes homologous to T2SS but dispersed on the bacterial chromosome. Components of these systems can either associate with classical T2SS components to constitute a functional hybrid machinery or represent peculiar systems with strictly defined functions.
The Type III Secretion System
Isabel Sorg and Guy R. Cornelis
The type-III secretion system (T3SS) is an export machine used by pathogenic Gram-negative bacteria to deliver proteins straight into the eukaryotic cytosol with the aim to subvert the host cell defense. After the discovery of T3S in 1990, significant progress has been made in the understanding of its structure, assembly and function. The basic structure consisting of the membrane-embedded basal body, the needle and the tip structure has been analyzed in more details. In the last years, the structure of several structural components has been solved and important insights into the assembly process have been gained. Furthermore, comparing the T3SS of pathogenic bacteria with the flagellum the relationship between these two structures becomes obvious. Besides the structural similarities, the assembly of these two nanomachines shows some commonalities like for example the length control of external structures like the T3 needle and the flagellar hook. In addition to the export machine the complete T3SS also includes the pore forming translocator proteins, effector proteins and a set of specific chaperones. Here, we review different aspects of the T3SS focusing on the structure and assembly of this fascinating nanomachine.
Mechanistic and Structural Analysis of Type IV Secretion Systems
Type IV secretion systems are multiprotein complexes that mediate the translocation of macromolecules (proteins, DNA or DNA-protein complexes) across the bacterial cell envelope into the extracellular medium or directly into recipient cells. This strategy is exploited for the delivery of effector molecules that modulate host cell interactions by bacterial pathogens and symbionts. Type IV secretion systems also mediate the translocation of DNA molecules from bacteria and the uptake of DNA into bacteria and thereby contribute to horizontal gene transfer. This review will discuss the state of knowledge on individual type IV secretion system components focusing on mechanistic and structural analyses. Based on these data, current models of the assembly of type IV secretion systems and of substrate translocation across the bacterial cell envelope will be presented. The review will conclude with a discussion of the remaining challenges, the future opportunities and novel approaches aimed at deciphering the function of these versatile macromolecule transporters.
Type V Secretion
Anthony Scott-Tucker and Ian R. Henderson
The Type V secretion system was first described twenty years ago. During the intervening years much work has be done to elucidate functional aspects of members of this family and their mechanisms of biogenesis. What was once considered to be a quirky one-off system, with the discovery of the IgA1 protease secretion system of Neisseria gonorrhoeae
, has been revealed as the largest family of secreted proteins amongst the Gram-negative bacteria. Here we review the current state of knowledge in the biogenesis of the T5SS, examining the steps involved in export across the inner membrane, transit through the periplasm, secretion across the outer membrane and folding of the secreted moiety on the cell surface.
Assembly and Secretion of Surface Fibres in Gram-negative Bacteria
David G. Thanassi, Matthew R. Chapman and Subhra Chakraborty
Bacteria assemble a variety of structures on their cell surface, including extended fibers generally termed pili or fimbriae. These fibers mediate interactions with other bacteria, the host, and the environment. Pili often function as adhesins, dictating specific binding to and colonization of biological as well as non-biological surfaces. As such, these fibers are critical virulence factors for pathogenic bacteria, initiating infection and determining how and where bacterial colonization may occur. This chapter will review the biogenesis of surface fibers by Gram-negative bacteria, with a focus on assembly mechanisms and machinery, and the structures of component proteins and the assembled organelles. The specific systems discussed in this chapter are the chaperone/usher pathway, alternate chaperone/usher pathway, extracellular nucleation/precipitation pathway (curli), and type IV pili.
Secretome Mapping in Gram-Positive Pathogens
Mark J.J.B. Sibbald and Jan Maarten van Dijl
Many diseases are caused by bacteria. While most infections are easy to treat with antibiotics, various bacteria seem to gain resistance against these antibiotics very rapidly. During the infective process bacteria need to express proteins that are necessary for colonization and spreading throughout the host tissue. Other proteins are needed for protecting the bacteria against attacks from the immune system or from other bacteria that belong to the normal human microbiota. All these proteins have to be transported across bacterial membrane(s) to be effective in host cell adhesion, function as agents for host cell subversion, and form protective responses to stressful conditions, for example during the process of phagocytosis. In Gram-positive bacteria, several pathways exist to transport these proteins across membranes. The fate of the translocated proteins then depends on the presence or absence of retention signals. This chapter deals with the secretion pathways existing in Gram-positive bacteria. The focus will be on the components of translocation pathways that are known to be involved in the recognition, translocation, and further processing of extracellular proteins and in particular virulence factors. Known pathways and current insights on new pathways will be discussed in relation to the secretion of (known) virulence factors.
Jannick D. Bendtsen and Karl G. Wooldridge
Bacterial secretion of proteins is undertaken by highly complex translocation machineries actively moving the protein to be secreted across the bacterial membrane. Given the complexity of these secretion systems it is not surprising that novel secretions systems are continuously being discovered. Neither is it surprising that we have limited knowledge on the secretory route for many known secretory proteins. Secreted proteins for which we lack information on the secretory route or where the secretory pathway is yet to be discovered are termed non-classical secretory proteins. Identification of new secretory pathways continuously move previously termed non-classical secretory proteins into new well-defined secretion systems. Many proteins secreted via alternative routes are involved in pathogenesis.
Section 2: Secreted Proteins of Bacterial Pathogens
Secreted Proteins and Virulence in Salmonella enterica
Secreted proteins are of major importance for the pathogenesis of infectious diseases caused by the facultative intracellular gastrointestinal pathogen Salmonella enterica
. A remarkable large number of fimbrial and non-fimbrial adhesins are present in Salmonella
and mediate biofilm formation as well as the intimate contact to host cells. The host cell invasion and intracellular proliferation are two hallmarks of Salmonella
deploys two type III secretion systems (T3SS) to translocate complex cocktails of effector proteins. Effectors translocated by the Salmonella
Pathogenicity Island 1 (SPI1)-T3SS mainly act on the host cell actin cytoskeleton resulting in the invasion of non-phagocytic cells. After entry, Salmonella
resides in the so-called Salmonella
-containing vacuole, from which translocation of a second set of effector proteins by the SPI2-T3SS initiated. The function of the SPI2-T3SS results intracellular replication and the modification of host cell vesicular traffic involving microtubules. Although classical exotoxins are not known as major virulence determinants of Salmonella
, recent data suggest a role of toxins encoded by the Salmonella
virulence plasmid. The concerted action of various secreted proteins allows Salmonella
to breach multiple barriers of host defense resulting in systemic infection and be development of a carrier state in some infected individuals.
Secreted and Exported Proteins Important to Mycobacterium tuberculosis Pathogenesis
Jessica R. McCann, Sherry Kurtz, and Miriam Braunstein
As with other bacterial pathogens, surface and secreted proteins of Mycobacterium tuberculosis
are important to virulence. Many of these M. tuberculosis
proteins are now known and significant progress is being made in identifying the systems responsible for their proper localization. There is also an increasing list of extracytoplasmic proteins proven to have a function in the virulence of M. tuberculosis
. In this Chapter, we review the current understanding of the protein transport systems of M. tuberculosis
and discuss some of the better characterized exported virulence factors of this important human pathogen.
Protein Secretion and Pathogenesis in Campylobacter jejuni
Neil J. Oldfield and Karl G. Wooldridge
is an important cause of human food-borne gastroenteritis that frequently colonizes poultry and contaminates their products. The high incidence of clinical disease associated with this bacterium, its low infective dose in humans and its potentially serious sequelae confirm its importance as a major public health hazard. Despite the medical and economic importance of C. jejuni
infection, fundamental aspects of the patho-physiology of colonization and infection remain poorly understood. Here, we present an overview of protein secretion in C. jejuni
and discuss the contribution of protein secretion systems to the pathogenesis and lifestyle of this bacterium. Both Sec dependent and TAT secretion systems are present. Of the protein secretion pathways that are widely disseminated among Gram-negative bacteria, only the type V (autotransporter) and a plasmid-encoded type IV-secretion system have been reported in C. jejuni
. A type II-like system involved in natural competence, a functional flagella export apparatus and an uncharacterized system mediating cytolethal distending toxin secretion are also discussed.
Mickaël Desvaux and Michel Hébraud
As a monoderm prokaryote, protein secretion systems in Listeria monocytogenes
are distinct from those encounter in diderm bacteria, still they remain the gates for expressing protein functions outside the intracellular bacterial cell compartment. Despite the fact that protein secretion is a key factor in virulence of a pathogen, fewer studies have been dedicated to pathogenic Gram-positive bacteria compared to Gram-negative bacteria and L. monocytogenes
is no exception. Among the six protein secretion systems identified in L. monocytogenes
, only proteins putatively translocated via the Sec pathway are indisputably involved in bacterial virulence. The 16 secreted virulence effectors characterised to date are either (i) associated with the cytoplasmic membrane, i.e. as integral membrane proteins or lipoproteins, (ii) associated with the cell wall, i.e. covalently in a sortase-dependent manner or via cell-wall binding domains, or (iii) released in the extracellular milieu. Identification of several candidates as putative secreted virulence factors as well as the availability in the near future of large amount of Listeria
genomic data from different sequencing projects are the promess of very exciting time in the field of listerial protein secretion and should provide further insights on how L. monocytogenes
interacts with its biotic or abiotic surroundings.
Protein Secretion and Pathogenesis in Neisseria meningitidis
David P. Turner, Karl G. Wooldridge and Dlawer A. A. Ala’Aldeen
is the agent of meningococcal meningitis and septicaemia: two devastating human diseases. It is becoming apparent that secreted proteins are likely to play important roles in meningococcal disease and, furthermore, meningococcal secreted proteins may constitute attractive components of vaccines or targets of therapeutic intervention. The meningococcus has been shown to secrete a large number of proteins, some of which are capable of modulating host cell gene expression. Of the major protein secretion pathways identified N. meningitidis
has been shown to secrete proteins via the Type I, autotransporter and two-component secretion pathways. Apart from genes encoding the Type IV pilus, the available meningococcal genomes do not appear to contain genes with homology to those encoding Type II, Type III or Type IV secretion systems, nor the recently described Type VI pathway.
Protein Secretion and Pathogenesis in Helicobacter pylori
Robin M. Delahay and Darren P. Letley
establishes a persistent colonisation of the human stomach which results in a chronic active gastritis. Approximately half the world population is infected with this bacterium, although the majority of infections are asymptomatic. However, persistent H. pylori
colonisation can lead to severe pathological outcomes, such as peptic ulcer disease and gastric adenocarcinoma, in a manner dependent upon host, environmental and bacterial factors. The two most extensively studied H. pylori
virulence factors are secreted products; the vacuolating cytotoxin, VacA, and CagA, an effector protein delivered by the cytotoxin-associated gene (cag) type IV secretion system. In addition to these major virulence determinants, H. pylori
releases many other proteins into its environment which contribute to the colonisation and pathogenesis of this organism. This chapter describes the known pathogenic role of some of these secreted factors with particular emphasis on VacA, CagA and the type IV secretion system encoded by the cag pathogenicity island.
Protein Secretion in Legionella pneumophila
Emmy De Buck, Elke Lammertyn and Jozef Anné
is a Gram-negative facultative intracellular pathogen, which in its natural environment multiplies in protozoa. This bacterium can also cause a severe pneumonia in man, better known as Legionnaires' disease, following infection of alveolar macrophages. L. pneumophila
enters its host cell by phagocytosis, creating a phagosome that does not fuse with lysosomes wherein bacteria can multiply. When nutrients are depleted, the bacteria enter the transmissive phase and express virulence proteins, resulting in lysis of host cells and the initiation of a new infection round. In each of these different stages of infection of host cells, virulence proteins need to be transported to their specific place of action. Several protein secretion systems have been identified in L. pneumophila
and most of them were shown to play an important role in the virulence of this pathogen. An overview will be given of all secretion pathways identified so far and special attention will be paid to those secretion systems involved in virulence.
Zoë E. V. Worthington and Nicholas H. Carbonetti
is a Gram-negative bacterial pathogen that infects the human respiratory tract, causing the disease pertussis or whooping cough. B. pertussis
produces a number of secreted virulence factors whose expression is coordinately regulated in response to environmental signals by the Bvg regulatory system. These virulence factors are secreted by a variety of different export pathways, including Type I, III, IV and V secretion systems. They are either cell-associated or released from the cell, and together they contribute to the pathogenic mechanisms employed by the bacteria to establish infection and cause disease. In this chapter, we discuss several of the better-characterized secreted virulence factors of B. pertussis
with regard to their structure, secretion and role in pathogenesis.
Secreted Proteins of Vibrio cholerae
Bethany Kay Boardman and Karla J. Fullner Satchell
The Gram-negative bacterium Vibrio cholerae
produces both surface-exposed and secreted factors essential for both its survival and growth in the environment and for induction of the diarrheal disease cholera. Surface-exposed factors include three different Type IV pili that mediate persistence in the intestine as well as surface colonization in the environment. In addition, these pili contribute to the evolution of the pathogen by serving as phage receptors or as a structure essential for DNA uptake. Secreted factors associated with disease include the major virulence factor Cholera Toxin (CT) that is responsible for the severe diarrhea associated with cholera disease. Additional secreted toxins, including hemolysin, hemagglutinin/protease, MARTXVc
, and Type III and Type VI effectors, have also been found to function in virulence and may significantly contribute to disease of non-CT producing non-O1/non-O139 strains. Export of some virulence factors is interconnected through signal pathways and secretion machineries with other secreted enzymes such as chitinases that are important for survival in the environment. Thus, V. cholerae
seems to have efficiently evolved to adapt to both intestinal and aquatic environments and utilizes secreted factors to modulate the environment to promote its own growth, survival, and dissemination.
The Secreted Proteins of Pseudomonas aeruginosa: Their Export Machineries, and How They Contribute to Pathogenesis
Kim R Hardie, Stephanie Pommier and Susanne Wilhelm
flourishes in hospital environments, and is a particular problem in this environment since it is the second most common infection in hospitalized patients. Perhaps this is because P. aeruginosa
is one of the most active protein secreting bacteria. Here we summarize this wide range of secretion machineries, detail the numerous protein substrates which they export, and relate this to the pathogenesis of two of the sequenced clinical strains (PAO1 and PA14). We hope that this will prove a useful resource complementing previous comparisons between P. aeruginosa
and the saprophytic plant symbiont P. fluorescens or other Pseudomonas
species including non pathogenic P. putida
Secretion Systems of the Enterobacterial Phytopathogen, Erwinia
Terry J. Evans, Daniel Pérez-Mendoza, Rita E. Monson, Hannah G. Stickland, and George P.C. Salmond
Sequencing of the phytopathogenic bacterium, Erwinia carotovora
revealed the presence of the six main bacterial secretion systems known to exist in Gram negative bacteria. The Erwinias have proven to be good experimental systems for investigating the mechanisms of protein secretion, and this is discussed in relation to Type I and Type II secretion. The physiological and pathogenic importance of the secretion systems is explained. A wide variety of proteins is exported by the Erwinias, and these secreted products play essential roles in adaptation to the environmental niches and lifestyles that the Erwinias are able to exploit. The physiological functions of this wide array of secreted proteins are discussed. A thorough bioinformatic analysis of the Type IV secretion system is presented - a system that impacts on virulence in Erwinia
, but which has not been heavily investigated experimentally. Finally, the contribution of horizontally acquired islands with respect to secretion is discussed.
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(EAN: 9781904455424 Subjects: [bacteriology] [microbiology] [medical microbiology] [molecular microbiology])