A two-component system serves as a central hub for connecting energy metabolism and plasmid dissemination in bacteria

Mobile genetic elements such as conjugative plasmids play a key role in the acquisition of antibiotic resistance by pathogenic bacteria. Resistance genes on plasmids can be transferred between bacteria using specialized conjugation machinery. Acinetobacter baumannii, the most common bacterium associated with nosocomial infections, harbors a large conjugative plasmid that encodes a type IV secretion system (T4SS). Feng et al. recently found that the A. baumannii T4SS is specialized for plasmid transfer, suggesting that it may be involved in multidrug resistance (Z. Feng, L. Wang, Q. Guan, X. Chu, and Z.-Q. Luo, mBio e02276-23, 2023, https://doi.org/10.1128/mbio.02276-23), T4SS-encoding genes are shown to be controlled by a versatile GacA/S two-component regulatory system. GacA/S is also found to regulate genes involved in central metabolism. The coordinated regulation of metabolism and plasmid conjugation may be a bacterial strategy for adapting to selective pressure from antibiotics.

Bacterial usurpation of the OTU deubiquitinase fold

The extensive cellular signalling events controlled by posttranslational ubiquitination are tightly regulated through the action of specialized proteases termed deubiquitinases. Among them, the OTU family of deubiquitinases can play very specialized roles in the regulation of discrete subtypes of ubiquitin signals that control specific cellular functions. To exert control over host cellular functions, some pathogenic bacteria have usurped the OTU deubiquitinase fold as a secreted virulence factor that interferes with ubiquitination inside infected cells. Herein, we provide a review of the function of bacterial OTU deubiquitinases during infection, the structural basis for their deubiquitinase activities and the bioinformatic approaches leading to their identification. Understanding bacterial OTU deubiquitinases holds the potential for discoveries not only in bacterial pathogenesis but in eukaryotic biology as well.

Mechanism of Lys6 poly-ubiquitin specificity by the L. pneumophila deubiquitinase LotA

The versatility of ubiquitination to control vast domains of eukaryotic biology is due, in part, to diversification through differently linked poly-ubiquitin chains. Deciphering signaling roles for some chain types, including those linked via K6, has been stymied by a lack of specificity among the implicated regulatory proteins. Forged through strong evolutionary pressures, pathogenic bacteria have evolved intricate mechanisms to regulate host ubiquitin during infection. Herein, we identify and characterize a deubiquitinase domain of the secreted effector LotA from Legionella pneumophila that specifically regulates K6-linked poly-ubiquitin. We demonstrate the utility of LotA for studying K6 poly-ubiquitin signals. We identify the structural basis of LotA activation and poly-ubiquitin specificity and describe an essential "adaptive" ubiquitin-binding domain. Without LotA activity during infection, the Legionella-containing vacuole becomes decorated with K6 poly-ubiquitin as well as the AAA ATPase VCP/p97/Cdc48. We propose that LotA's deubiquitinase activity guards Legionella-containing vacuole components from ubiquitin-dependent extraction.

Requirement of phosphatidic acid binding for distribution of bacterial protein targeting syntaxin 17

A gram-negative bacterium, Legionella pneumophila is known to manipulate the host cellular functions. In these manipulations, bacterial proteins called Legionella effectors that L. pneumophila secretes into the host cytosol are necessary. A Legionella effector, Lpg1137, was identified as a serine protease responsible for degradation of syntaxin 17 (Stx17). However, how Lpg1137 can specifically recognize and degrade Stx17 remains unknown. Given that Stx17 is localized in the ER/mitochondria-associated membrane (MAM)/mitochondria, Lpg1137 likely distributes to these compartments to recognize Stx17. Here we show that the C-terminal region of Lpg1137 binds to phosphatidic acid (PA), a MAM/mitochondria-enriched phospholipid, and that this binding is required for the correct intracellular distribution of Lpg1137. Two basic residues in the C-terminal region are required for PA binding and their mutation causes mislocalization of Lpg1137. This mutant fails to degrade Stx17 while retaining a protease activity. Taken together, our data reveal that Lpg1137 utilizes PA for its distribution to the membranous compartments in which Stx17 is localized.

Recent advances in structural studies of the Legionella pneumophila Dot/Icm type IV secretion system

The intracellular bacterial pathogen Legionella pneumophila utilizes the Dot/Icm type IV secretion system to translocate approximately 300 effector proteins to establish a replicative niche known as the Legionella‐containing vacuole. The Dot/Icm system is classified as a type IVB secretion system, which is evolutionarily closely related to the I‐type conjugation systems and is distinct from type IVA secretion systems, such as the Agrobacterium VirB/D4 system. Although both type IVA and IVB systems directly transport nucleic acids or proteins into the cytosol of recipient cells, the components and architecture of type IVB systems are much more complex than those of type IVA systems. Taking full advantage of rapidly developing cryo‐electron microscopy techniques, the structural details of the transport apparatus and coupling complexes in the Dot/Icm system have been clarified in the past few years. In this review, we summarize recent progress in the structural studies of the L. pneumophila type IVB secretion system and the insights gained into the mechanisms of substrate recognition and transport.

Legionella Manipulates Non-canonical SNARE Pairing Using a Bacterial Deubiquitinase

The intracellular bacterial pathogen Legionella pneumophila uses many effector proteins delivered by the bacterial type IV secretion system (T4SS) to hijack the early secretory pathway to establish its replicative niche, known as the Legionella-containing vacuole (LCV). On LCV biogenesis, the endoplasmic reticulum (ER) vesicular soluble N-ethylmaleimide-sensitive factor attachment protein receptors (v-SNARE) Sec22b is recruited to the bacterial phagosome and forms non-canonical pairings with target membrane SNAREs (t-SNAREs) from the plasma membrane. Here, we identify a Legionella deubiquitinase (DUB), LotB, that can modulate the early secretory pathway by interacting with coatomer protein complex I (COPI) vesicles when ectopically expressed. We show that Sec22b is ubiquitinated upon L. pneumophila infection in a T4SS-dependent manner and that, subsequently, LotB deconjugates K63-linked ubiquitins from Sec22b. The DUB activity of LotB stimulates dissociation of the t-SNARE syntaxin 3 (Stx3) from Sec22b, which resides on the LCV. Our study highlights a bacterial strategy manipulating the dynamics of infection-induced SNARE pairing using a bacterial DUB.

Protocol for imaging proteins associated with Legionella-containing vacuoles in host cells

The intracellular bacterial pathogen Legionella pneumophila exploits host cellular systems using approximately 300 effector proteins to establish a replicative niche known as the Legionella-containing vacuole (LCV). During infection, both host and bacterial proteins interactively function on the LCVs. Here, we describe a detailed step-by-step protocol to visualize proteins associated with LCVs in host cells. This protocol can aid in analyzing whether a protein of interest influences the subcellular localization of LCV-associated proteins during infection.

For complete details on the use and execution of this protocol, please refer to Kitao et al. (2020).

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Step-by-step workflow describing how to infect host cells with intracellular bacteria

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Identification of subcellular localization of bacterial proteins in host cells

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Analysis of cellular reorganization of host proteins as a result of infection

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Protocol is applicable to any intracellular bacteria

Isolation and Characterization of a Novel Phage SaGU1 that Infects Staphylococcus aureus Clinical Isolates from Patients with Atopic Dermatitis

The bacterium Staphylococcus aureus, which colonizes healthy human skin, may cause diseases, such as atopic dermatitis (AD). Treatment for such AD cases involves antibiotic use; however, alternate treatments are preferred owing to the development of antimicrobial resistance. This study aimed to characterize the novel bacteriophage SaGU1 as a potential agent for phage therapy to treat S. aureus infections. SaGU1 that infects S. aureus strains previously isolated from the skin of patients with AD was screened from sewage samples in Gifu, Japan. Its genome was sequenced and analyzed using bioinformatics tools, and the morphology, lytic activity, stability, and host range of the phage were determined. The SaGU1 genome was 140,909 bp with an average GC content of 30.2%. The viral chromosome contained 225 putative protein-coding genes and four tRNA genes, carrying neither toxic nor antibiotic resistance genes. Electron microscopy analysis revealed that SaGU1 belongs to the Myoviridae family. Stability tests showed that SaGU1 was heat-stable under physiological and acidic conditions. Host range testing revealed that SaGU1 can infect a broad range of S. aureus clinical isolates present on the skin of AD patients, whereas it did not kill strains of Staphylococcus epidermidis, which are symbiotic resident bacteria on human skin. Hence, our data suggest that SaGU1 is a potential candidate for developing a phage therapy to treat AD caused by pathogenic S. aureus.

Staphylococcal Phage in Combination with Staphylococcus Epidermidis as a Potential Treatment for Staphylococcus Aureus-Associated Atopic Dermatitis and Suppressor of Phage-Resistant Mutants

Atopic dermatitis is accompanied by the abnormal overgrowth of Staphylococcus aureus, a common cause of skin infections and an opportunistic pathogen. Although administration of antibiotics is effective against S. aureus, the resulting reduction in healthy microbiota and the emergence of drug-resistant bacteria are of concern. We propose that phage therapy can be an effective strategy to treat atopic dermatitis without perturbing the microbiota structure. In this study, we examined whether the S. aureus phage SaGU1 could be a tool to counteract the atopic exacerbation induced by S. aureus using an atopic mouse model. Administration of SaGU1 to the back skin of mice reduced both S. aureus counts and the disease exacerbation caused by S. aureus. Furthermore, the S. aureus-mediated exacerbation of atopic dermatitis with respect to IgE plasma concentration and histopathological findings was ameliorated by the application of SaGU1. We also found that Staphylococcus epidermidis, a typical epidermal symbiont in healthy skin, significantly attenuated the emergence of SaGU1-resistant S. aureus under co-culture with S. aureus and S. epidermidis in liquid culture infection experiments. Our results suggest that phage therapy using SaGU1 could be a promising clinical treatment for atopic dermatitis.

Divergence of Legionella Effectors Reversing Conventional and Unconventional Ubiquitination

The intracellular bacterial pathogen Legionella pneumophila employs bacteria-derived effector proteins in a variety of functions to exploit host cellular systems. The ubiquitination machinery constitutes a crucial eukaryotic system for the regulation of numerous cellular processes, and is a representative target for effector-mediated bacterial manipulation. L. pneumophila transports over 300 effector proteins into host cells through its Dot/Icm type IV secretion system. Among these, several effector proteins have been found to function as ubiquitin ligases, including unprecedented enzymes that catalyze ubiquitination through unconventional mechanisms. Recent studies have identified many L. pneumophila effector proteins that can interfere with ubiquitination. These effectors include proteins that are distantly related to the ovarian tumor protein superfamily described as deubiquitinases (DUBs), which regulate important signaling cascades in human cells. Intriguingly, L. pneumophila DUBs are not limited to enzymes that exhibit canonical DUB activity. Some L. pneumophila DUBs can catalyze the cleavage of the unconventional linkage between ubiquitin and substrates. Furthermore, novel mechanisms have been found that adversely affect the function of specific ubiquitin ligases; for instance, effector-mediated posttranslational modifications of ubiquitin ligases result in the inhibition of their activity. In the context of L. pneumophila infection, the existence of enzymes that reverse ubiquitination primarily relates to a fine tuning of biogenesis and remodeling of the Legionella-containing vacuole as a replicative niche. The complexity of the effector arrays reflects sophisticated strategies that bacteria have adopted to adapt their host environment and enable their survival in host cells. This review summarizes the current state of knowledge on the divergent mechanisms of the L. pneumophila effectors that can reverse ubiquitination, which is mediated by other effectors as well as the host ubiquitin machinery.

Structural basis for effector protein recognition by the Dot/Icm Type IVB coupling protein complex

The Legionella pneumophila Dot/Icm type IVB secretion system (T4BSS) is extremely versatile, translocating ~300 effector proteins into host cells. This specialized secretion system employs the Dot/Icm type IVB coupling protein (T4CP) complex, which includes IcmS, IcmW and LvgA, that are known to selectively assist the export of a subclass of effectors. Herein, the crystal structure of a four-subunit T4CP subcomplex bound to the effector protein VpdB reveals an interaction between LvgA and a linear motif in the C-terminus of VpdB. The same binding interface of LvgA also interacts with the C-terminal region of three additional effectors, SidH, SetA and PieA. Mutational analyses identified a FxxxLxxxK binding motif that is shared by VpdB and SidH, but not by SetA and PieA, showing that LvgA recognizes more than one type of binding motif. Together, this work provides a structural basis for how the Dot/Icm T4CP complex recognizes effectors, and highlights the multiple substrate-binding specificities of its adaptor subunit.

Subversion of Host Membrane Dynamics by the Legionella Dot/Icm Type IV Secretion System

Legionella species are Gram-negative ubiquitous environmental bacteria, which thrive in biofilms and parasitize protozoa. Employing an evolutionarily conserved mechanism, the opportunistic pathogens also replicate intracellularly in mammalian macrophages. This feature is a prerequisite for the pathogenicity of Legionella pneumophila, which causes the vast majority of clinical cases of a severe pneumonia, termed "Legionnaires' disease." In macrophages as well as in amoeba, L. pneumophila grows in a distinct membrane-bound compartment, the Legionella-containing vacuole (LCV). Formation of this replication-permissive pathogen compartment requires the bacterial Dot/Icm type IV secretion system (T4SS). Through the T4SS as many as 300 different "effector" proteins are injected into host cells, where they presumably subvert pivotal processes. Less than 40 Dot/Icm substrates have been characterized in detail to date, a number of which show unprecedented biological activities. Some of these effector proteins target host cell small GTPases, phosphoinositide lipids, the chelator phytate, the ubiquitination machinery, the retromer complex, the actin cytoskeleton, or the autophagy pathway. A recently discovered class of L. pneumophila effectors modulates the activity of other effectors and is termed "metaeffectors." Here, we summarize recent insight into the cellular functions and biochemical activities of L. pneumophila effectors and metaeffectors targeting the host's endocytic, retrograde, or autophagic pathways.

LotA, a Legionella deubiquitinase, has dual catalytic activity and contributes to intracellular growth

The intracellular bacterial pathogen, Legionella pneumophila, establishes the replicative niche as a result of the actions of a large array of effector proteins delivered via the Legionella Type 4 secretion system. Many effector proteins are expected to be involved in biogenesis and regulation of the Legionella-containing vacuole (LCV) that is highly decorated with ubiquitin. Here, we identified a Legionella deubiquitinase, designated LotA, by carrying out a genome analysis to find proteins resembling the eukaryotic ovarian tumour superfamily of cysteine proteases. LotA exhibits a dual ability to cleave ubiquitin chains that is dependent on 2 distinctive catalytic cysteine residues in the eukaryotic ovarian tumour domains. One cysteine dominantly contributes to the removal of ubiquitin from the LCVs by its polyubiquitin cleavage activity. The other specifically cleaves conjugated Lys6-linked ubiquitin. After delivered by the Type 4 secretion system, LotA localises on the LCVs via its PI(3)P-binding domain. The lipid-binding ability of LotA is crucial for ubiquitin removal from the vacuoles. We further analysed the functional interaction of the protein with the recently reported noncanonical ubiquitin ligases of L. pneumophila, revealing that the effector proteins are involved in coordinated regulation that contributes to bacterial growth in the host cells.

Legionella RavZ Plays a Role in Preventing Ubiquitin Recruitment to Bacteria-Containing Vacuoles

Bacterial pathogens like Salmonella and Legionella establish intracellular niches in host cells known as bacteria-containing vacuoles. In these vacuoles, bacteria can survive and replicate. Ubiquitin-dependent selective autophagy is a host defense mechanism to counteract infection by invading pathogens. The Legionella effector protein RavZ interferes with autophagy by irreversibly deconjugating LC3, an autophagy-related ubiquitin-like protein, from a phosphoglycolipid phosphatidylethanolamine. Using a co-infection system with Salmonella, we show here that Legionella RavZ interferes with ubiquitin recruitment to the Salmonella-containing vacuoles. The inhibitory activity is dependent on the same catalytic residue of RavZ that is involved in LC3 deconjugation. In semi-permeabilized cells infected with Salmonella, external addition of purified RavZ protein, but not of its catalytic mutant, induced removal of ubiquitin associated with Salmonella-containing vacuoles. The RavZ-mediated restriction of ubiquitin recruitment to Salmonella-containing vacuoles took place in the absence of the host system required for LC3 conjugation. These observations suggest the possibility that the targets of RavZ deconjugation activity include not only LC3, but also ubiquitin.

Isolation of the Dot/Icm Type IV Secretion System Core Complex from Legionella pneumophila for Negative Stain Electron Microscopy Studies

Legionella possesses a pivotal secretion machinery to deliver virulence factors to eukaryotic host cells. In this protocol, we describe the procedure for isolation of the native core complex of the Dot/Icm type IV secretion system from L. pneumophila aiming to perform biochemical and transmission electron microscopy analyses.

Hijacking the host proteasome for the temporal degradation of bacterial effectors

To establish infection, intracellular pathogens need to modulate host cellular processes. Modulation of host processes is achieved by the action of various "effector proteins" which are delivered from the bacteria to the host cell cytosol. In order to orchestrate host cell reprogramming, the function of effectors inside host cells is regulated both temporally and spatially. In eukaryotes one of the most prominent processes used to degrade proteins is the ubiquitin-proteasome system. Recently it has emerged that the intracellular pathogen Legionella pneumophila is able to achieve temporal regulation of an effector using the ubiquitin-proteasome system. After establishing its replicative niche, the L. pneumophila effector SidH is degraded by the host proteasome. Most remarkably another effector protein LubX is able to mimic the function of an eukaryotic E3 ubiquitin ligase and polyubiquitinates SidH, targeting it for degradation. In this paper we describe a method to detect the polyubiquitin-modified forms of SidH in vitro and in vivo. Analyzing the temporal profile of polyubiquitination and degradation of bacterial effectors aids towards our understanding of how bacteria hijack host systems.

Purification and characterization of legionella U-box-type E3 ubiquitin ligase

Bacterial virulence proteins often mimic host eukaryotic proteins to modify or disturb host cellular -pathways. Increasing lines of evidence show that many bacterial effector proteins have E3 ubiquitin ligase activity. The effector protein LubX is one such bacterial E3 ubiquitin ligase. We describe here the method to purify soluble LubX protein using GST-tag and Escherichia coli overexpression systems. Using the purified protein together with recombinant ubiquitin, E1, and E2 enzymes, ubiquitin ligase activity is analyzed by the in vitro ubiquitination assay.

Bacterial effector-involved temporal and spatial regulation by hijack of the host ubiquitin pathway

Ubiquitination is one of the most conserved post-translational modifications of proteins, and is involved in essential eukaryotic cellular processes. These include protein degradation, transcriptional regulation, cell-cycle progression, and signaling. Microbial pathogens have evolved sophisticated systems to hijack host cellular functions for their own benefit. Central to these systems are protein transport machineries; many pathogenic bacteria inject "effector proteins" to modulate host cellular processes including the ubiquitin pathway. Numerous bacterial pathogens have been found to modulate the host ubiquitin system in various ways. In this review, we focus on three examples of temporal and spatial regulation of bacterial effectors, which are mediated by the host ubiquitin system. Subversion of the host ubiquitin system must be a widespread strategy among pathogenic bacteria to accomplish successful infection.

Type IVB Secretion Systems of Legionella and Other Gram-Negative Bacteria

Type IV secretion systems (T4SSs) play a central role in the pathogenicity of many important pathogens, including Agrobacterium tumefaciens, Helicobacter pylori, and Legionella pneumophila. The T4SSs are related to bacterial conjugation systems, and are classified into two subgroups, type IVA (T4ASS) and type IVB (T4BSS). The T4BSS, which is closely related to conjugation systems of IncI plasmids, was originally found in human pathogen L. pneumophila; pathogenesis by L. pneumophila infection requires functional Dot/Icm T4BSS. A zoonotic pathogen, Coxiella burnetii, and an arthropod pathogen, Rickettsiella grylli – both of which carry T4BSSs highly similar to the Legionella Dot/Icm system – are evolutionarily closely related and comprise a monophyletic group. A growing body of bacterial genomic information now suggests that T4BSSs are not limited to Legionella and related bacteria and IncI plasmids. Here, we review the current knowledge on T4BSS apparatus and component proteins, gained mainly from studies on L. pneumophila Dot/Icm T4BSS. Recent structural studies, along with previous findings, suggest that the Dot/Icm T4BSS contains components with primary or higher-order structures similar to those in other types of secretion systems – types II, III, IVA, and VI, thus highlighting the mosaic nature of T4BSS architecture.

Legionella metaeffector exploits host proteasome to temporally regulate cognate effector

Pathogen-associated secretion systems translocate numerous effector proteins into eukaryotic host cells to coordinate cellular processes important for infection. Spatiotemporal regulation is therefore important for modulating distinct activities of effectors at different stages of infection. Here we provide the first evidence of "metaeffector," a designation for an effector protein that regulates the function of another effector within the host cell. Legionella LubX protein functions as an E3 ubiquitin ligase that hijacks the host proteasome to specifically target the bacterial effector protein SidH for degradation. Delayed delivery of LubX to the host cytoplasm leads to the shutdown of SidH within the host cells at later stages of infection. This demonstrates a sophisticated level of coevolution between eukaryotic cells and L. pneumophila involving an effector that functions as a key regulator to temporally coordinate the function of a cognate effector protein.

Crystal structure of Legionella DotD: insights into the relationship between type IVB and type II/III secretion systems

The Dot/Icm type IVB secretion system (T4BSS) is a pivotal determinant of Legionella pneumophila pathogenesis. L. pneumophila translocate more than 100 effector proteins into host cytoplasm using Dot/Icm T4BSS, modulating host cellular functions to establish a replicative niche within host cells. The T4BSS core complex spanning the inner and outer membranes is thought to be made up of at least five proteins: DotC, DotD, DotF, DotG and DotH. DotH is the outer membrane protein; its targeting depends on lipoproteins DotC and DotD. However, the core complex structure and assembly mechanism are still unknown. Here, we report the crystal structure of DotD at 2.0 Å resolution. The structure of DotD is distinct from that of VirB7, the outer membrane lipoprotein of the type IVA secretion system. In contrast, the C-terminal domain of DotD is remarkably similar to the N-terminal subdomain of secretins, the integral outer membrane proteins that form substrate conduits for the type II and the type III secretion systems (T2SS and T3SS). A short β-segment in the otherwise disordered N-terminal region, located on the hydrophobic cleft of the C-terminal domain, is essential for outer membrane targeting of DotH and Dot/Icm T4BSS core complex formation. These findings uncover an intriguing link between T4BSS and T2SS/T3SS.

Bacterial pathogens deliver virulence factors such as exotoxins and effector proteins to host cells. To accomplish this bacteria utilize specialized secretion systems such as type III and type IV secretion systems. The type IV secretion systems (T4SS) play a central role in pathogenesis by many important pathogens including Agrobacterium tumefaciens, Helicobacter pylori and Legionella pneumophila. T4SS is ancestrally related to the bacterial conjugation system and is divided into two subgroups, type IVA (T4ASS) and type IVB (T4BSS), which are derived from distinct conjugation systems. In spite of its pivotal role in bacterial pathogenesis, the structural bases and molecular mechanisms of the type IVB secretion still remain largely unknown. Here we show the crystal structure of DotD, one of the core components of Legionella T4BSS. Surprisingly, the structure of DotD is not related to those of T4ASS core components. In contrast, the structure of DotD is remarkably similar to that of a subdomain of secretin family proteins, which form substrate conduits for other types of secretion systems. This finding provides intriguing insights into the nature and the evolution of bacterial secretion systems essential for pathogenesis.

Dementia in Parkinson's disease: diffusion tensor imaging

OBJECTIVE

Dementia occurs frequently in patients with Parkinson's disease (PD). However, the nature of the dementing process remains controversial. We evaluated various cognitive functions in patients with PD, compared fractional anisotropy (FA) values between PD patients with and without dementia.

METHODS

Thirty-seven consecutive patients with Hoehn-Yahr stage III or IV PD participated in this study. Patients were divided into two groups: (i) PD with dementia group (PDD) and (ii) PD without dementia group (PDND). There were 11 PDD and 26 PDND cases. Ten controls were also studied.

RESULTS

The PDD group showed significant FA reduction in the bilateral posterior cingulate bundles compared with PDND. FA values in the left posterior cingulate bundle showed significant correlations with many cognitive parameters.

INTERPRETATION

Our results showed that the posterior cingulate areas play some important roles in the dementing process in PDD. However, as the pathological processes responsible for dementia in PD patients may be multifaceted, further studies are necessary.

Wisconsin Card Sorting Test in Parkinson's disease: diffusion tensor imaging

INTRODUCTION

It is generally assumed that executive dysfunctions in Parkinson's disease (PD) are caused by degeneration of the basal ganglia or frontal cortex or both. However, there have been few studies investigating the relationship between executive dysfunctions and cerebral pathological change. The objective of this study was to evaluate various cognitive functions in non-demented patients with PD, and to compare the fractional anisotropy (FA) values of PD patients with and without executive dysfunction.

MATERIALS AND METHODS

Twenty-one consecutive non-demented patients with PD were enrolled in this study. Patients were divided into two groups on the basis of their Wisconsin Card Sorting Test score.

RESULTS

There was significant FA reduction in the left parietal white matter in the group in which the number of categories achieved was <or=2 relative to the group that achieved >2.

CONCLUSION

Accumulating evidence suggests that conventional 'frontal' tasks correlate with both frontal lobe and parietal lobe function, and we suggest that pathological changes in the left parietal lobe may cause, in part, disturbances in executive tasks in PD.

Assembly of the inner rod determines needle length in the type III secretion injectisome

Assembly of multi-component supramolecular machines is fundamental to biology, yet in most cases, assembly pathways and their control are poorly understood. An example is the type III secretion machine, which mediates the transfer of bacterial virulence proteins into host cells. A central component of this nanomachine is the needle complex or injectisome, an organelle associated with the bacterial envelope that is composed of a multi-ring base, an inner rod, and a protruding needle. Assembly of this organelle proceeds in sequential steps that require the reprogramming of the secretion machine. Here we provide evidence that, in Salmonella typhimurium, completion of the assembly of the inner rod determines the size of the needle substructure. Assembly of the inner rod, which is regulated by the InvJ protein, triggers conformational changes on the cytoplasmic side of the injectisome, reprogramming the secretion apparatus to stop secretion of the needle protein.

A pathway branching in transcription initiation in Escherichia coli

In transcription initiation, all RNA polymerase molecules bound to a promoter have been conventionally supposed to proceed into elongation of transcript. However, for Escherichia coli RNA polymerase, evidence has been accumulated for a view that only its fraction can proceed into elongation and the rest is retained at a promoter in non-productive form: a pathway branching in transcription initiation. Proteins such as GreA and GreB affect these fractions at several promoters in vitro. To reveal the ubiquitous existence of the branched mechanism in E. coli, we searched for candidate genes whose transcription decreased by disruption of greA and greB using a DNA array. Among the arbitrarily selected 11 genes from over 100, the atpC, cspA and rpsA passed the test by Northern blotting. The Gre factors activated transcription initiation from their promoters in vitro, and the results demonstrated that the branched mechanism is exploited in vivo regulation. Consistently, decrease in the level of the GreA in an anaerobic stationary condition accompanied a decrease in the levels of transcripts of these genes.

Three-dimensional stereotactic surface projection study of orthostatic hypotension and brain perfusion image in Parkinson's disease

OBJECTIVE

To compare brain perfusion image using three-dimensional stereotactic surface projection (3D-SSP) analysis of N-isopropyl-p-123I iodoamphetamine (123I-IMP) single photon emission computed tomography (SPECT) between patients with Parkinson's disease with orthostatic hypotension and those without orthostatic hypotension.

MATERIALS AND METHODS

Fifteen patients with Parkinson's disease and orthostatic hypotension and 13 patients with Parkinson's disease without orthostatic hypotension were studied. We compared brain perfusion image between the two groups by 3D-SSP.

RESULTS

Bilateral anterior cingulate gyrus perfusion of the patients with orthostatic hypotension was significantly decreased compared to that of the patients without orthostatic hypotension.

CONCLUSIONS

The disorder of anterior cingulate gyrus may participate in the autonomic failure in Parkinson's disease.

CD16+CD57– Natural Killer Cells in Multifocal Motor Neuropathy

We analyzed the CD16+CD57- lymphocyte subset, which is considered to have strong natural killer (NK) cell activity, in peripheral blood from patients with chronic immune-mediated neuropathies and patients with other neurological diseases. We found that the ratio of CD16+CD57- NK cells to total lymphocytes was increased in 4 of 6 patients with multifocal motor neuropathy (MMN) with persistent conduction block. Since the CD16 molecule is an Fc receptor for immunoglobulin G (IgG), high-dose intravenous immunoglobulin (IVIg) may interfere with CD16+CD57- NK cells via Fc receptor blockade. In addition, cyclophosphamide (Cy) is often used to suppress NK cells. Therefore, our findings may partly account for the effectiveness of IVIg or Cy, which is the current treatment of choice for MMN.

Structural insights into the assembly of the type III secretion needle complex

Type III secretion systems (TTSSs) mediate translocation of virulence factors into host cells. We report the 17-angstrom resolution structures of a central component of Salmonella typhimurium TTSS, the needle complex, and its assembly precursor, the bacterial envelope-anchored base. Both the base and the fully assembled needle complex adopted multiple oligomeric states in vivo, and needle assembly was accompanied by recruitment of the protein PrgJ as a structural component of the base. Moreover, conformational changes during needle assembly created scaffolds for anchoring both PrgJ and the needle substructure and may provide the basis for substrate-specificity switching during type III secretion.

Disruption of type III secretion in Salmonella enterica serovar Typhimurium by external guide sequences

The type III secretion system involved in Salmonella enterica serovar Typhimurium invasion of host cells has been disrupted using inducibly expressed oligonucleotide external guide sequences (EGSs) complementary to invB or invC mRNA. These EGSs direct single site cleavage in these mRNAs by endogenous RNase P, and their expression in Salmonella results in invC mRNA and InvC protein depletion, decreased type III secretion and interference with host cell invasion. Comparison of these effects with those from studies of Salmonella invB and invC mutants suggests that invB EGSs have polar effects on invC mRNA.

Temporal regulation of salmonella virulence effector function by proteasome-dependent protein degradation

Salmonella enterica invasion of host cells requires the reversible activation of the Rho-family GTPases Cdc42 and Rac1 by the bacterially encoded GEF SopE and the GAP SptP, which exert their function at different times during infection and are delivered into host cells by a type III secretion system. We found that SopE and SptP are delivered in equivalent amounts early during infection. However, SopE is rapidly degraded through a proteosome-mediated pathway, while SptP exhibits much slower degradation kinetics. The half-lives of these effector proteins are determined by their secretion and translocation domains. Chimeric protein analysis indicated that delivery of SptP into host cells by the SopE secretion and translocation domain drastically shortened its half-life. Conversely, delivery of SopE by the SptP secretion and translocation signals significantly increased its half-life, resulting in persistent actin cytoskeleton rearrangements. This regulatory mechanism constitutes a remarkable example of a pathogen's adaptation to modulate cellular functions.

Synthesis and localization of the Salmonella SPI-1 type III secretion needle complex proteins PrgI and PrgJ

An essential component of type III secretion systems (TTSS) is a supramolecular structure termed the needle complex. In Salmonella enterica, at least four proteins make up this structure: InvG, PrgH, PrgK, and PrgI. Another protein, PrgJ, is thought to play a role in the assembly of this structure, but its function is poorly understood. We have analyzed the expression and localization of PrgJ and the needle protein PrgI in different S. enterica serovar Typhimurium mutant strains. We found that the levels of PrgI and PrgJ were significantly reduced in a TTSS-deficient invA mutant strain and that the decreased levels were due to protein instability. In addition, we found that PrgJ, although associated with the needle complex in wild-type S. enterica serovar Typhimurium, was absent from needle complexes obtained from an invJ mutant strain, which exhibits very long needle substructures. We suggest that PrgJ is involved in capping the needle substructure of the needle complex.

Molecular and functional analysis of the type III secretion signal of the Salmonella enterica InvJ protein

Central to the pathogenicity of Salmonella enterica is the function of a type III secretion system (TTSS) encoded within a pathogenicity island at centisome 63 (SPI-1). An essential component of this system is a supramolecular structure termed the needle complex. Proteins to be delivered into host cells possess specific signals that route them to the type III secretion pathway. In addition, some bacterial proteins have signals that deliver them to the secretion complex to either become their structural components or exert their function at that location. One of these proteins is InvJ, which controls the length of the needle substructure of the needle complex. In this study, we have analysed the signal that targets InvJ to the TTSS. We found that amino acid residues 4 to 7 of InvJ are necessary and sufficient to mediate secretion of InvJ or a reporter protein in a TTSS-dependent manner. InvJ secretion was found to be essential for its function in needle length determination, effector protein secretion and bacterial invasion of epithelial cells. Frameshift mutagenesis analysis indicated that the InvJ type III secretion signal sequence tolerates significant alterations in its amino acid sequence without affecting InvJ secretion. Introduction of silent mutations in the secretion signal coding sequence that result in drastically different predicted mRNA folds had no effect on InvJ secretion or expression.

Salmonella type III secretion-associated protein InvE controls translocation of effector proteins into host cells

Salmonella enterica encodes a type III secretion system (TTSS) within a pathogenicity island located at centisome 63 (SPI-1), which is essential for its pathogenicity. This system mediates the transfer of a battery of bacterial proteins into the host cell with the capacity to modulate cellular functions. The transfer process is dependent on the function of protein translocases SipB, SipC, and SipD. We report here that Salmonella protein InvE, which is also encoded within SPI-1, is essential for the translocation of bacterial proteins into host cells. An S. enterica serovar Typhimurium mutant carrying a loss-of-function mutation in invE shows reduced secretion of SipB, SipC, and SipD while exhibiting increased secretion of other TTSS effector proteins. We also demonstrate that InvE interacts with a protein complex formed by SipB, SipC, and their cognate chaperone, SicA. We propose that InvE controls protein translocation by regulating the function of the Sip protein translocases.

Genetic analysis of assembly of the Salmonella enterica serovar Typhimurium type III secretion-associated needle complex

Several pathogenic bacteria have evolved a specialized protein secretion system termed type III to secrete and deliver effector proteins into eukaryotic host cells. Salmonella enterica serovar Typhimurium uses one such system to mediate entry into nonphagocytic cells. This system is composed of more than 20 proteins which are encoded within a pathogenicity island (SPI-1) located at centisome 63 of its chromosome. A subset of these components form a supramolecular structure, termed the needle complex, that resembles the flagellar hook-basal body complex. The needle complex is composed of a multiple-ring cylindrical base that spans the bacterial envelope and a needle-like extension that protrudes from the bacterial outer surface. Although the components of this structure have been identified, little is known about its assembly. In this study we examined the effect of loss-of-function mutations in each of the type III secretion-associated genes encoded within SPI-1 on the assembly of the needle complex. This analysis indicates that the assembly of this organelle occurs in discrete, genetically separable steps. A model for the assembly pathway of this important organelle is proposed that involves a sec-dependent step leading to the assembly of the base substructure followed by a sec-independent process resulting in the assembly of the needle portion.

[Cerebral infarction presenting pure motor monoparesis: diagnosis by diffusion-weighted MR imaging]

We studied 10 patients with acute ischemic cerebrovascular disorders presenting paralysis confined to one limb, unaccompanied by sensory signs(pure motor monoparesis, PMM) on diffusion-weighted MR imaging(DWI). DWI revealed fresh ischemic lesions in all patients, except for 2 cases of transient ischemic attack. On DWI, acute infarction in multiple lesions was identified, and small superficial lesions were clearly described. Superficial lesions were seen in 4 patients, and deep lesions were also seen in 4 patients. DWI is useful for lesion analysis in cerebral infarction with PMM.

Molecular characterization and assembly of the needle complex of the Salmonella typhimurium type III protein secretion system

Many bacterial pathogens of plants and animals have evolved a specialized protein-secretion system termed type III to deliver bacterial proteins into host cells. These proteins stimulate or interfere with host cellular functions for the pathogen's benefit. The Salmonella typhimurium pathogenicity island 1 encodes one of these systems that mediates this bacterium's ability to enter nonphagocytic cells. Several components of this type III secretion system are organized in a supramolecular structure termed the needle complex. This structure is made of discrete substructures including a base that spans both membranes and a needle-like projection that extends outward from the bacterial surface. We demonstrate here that the type III secretion export apparatus is required for the assembly of the needle substructure but is dispensable for the assembly of the base. We show that the length of the needle segment is determined by the type III secretion associated protein InvJ. We report that InvG, PrgH, and PrgK constitute the base and that PrgI is the main component of the needle of the type III secretion complex. PrgI homologs are present in type III secretion systems from bacteria pathogenic for animals but are absent from bacteria pathogenic for plants. We hypothesize that the needle component may establish the specificity of type III secretion systems in delivering proteins into either plant or animal cells.

[A case of acute motor sensory axonal polyneuropathy after Haemophilus influenzae infection]

A 47-year-old woman developed consciousness disturbance, and experienced hallucinations while traveling abroad, and then went into critical condition. She was placed in the critical care unit, and had flaccid tetraparesis requiring mechanical ventilation. Haemophilus influenzae was cultured from the sputum. The level of protein of the cerebrospinal fluid was elevated to 114 mg/dl, nerve conduction study showed findings of pure axonal damage, and the sural nerve biopsy revealed severe axonal degeneration. She improved gradually by plasma exchange. The diagnosis of acute motor sensory axonal polyneuropathy (AMSAN) based on autoimmune mechanism was made. We speculate that H. influenzae infection may have elicited AMSAN in this case.

[A juvenile case of chronic inflammatory demyelinating polyradiculoneuropathy with severe onion bulb-like change mimicking hereditary neuropathy]

A 15-year-old male developed symmetrical weakness of the limb muscles. He had not had any previous developmental disorders except delayed initiation of walking. Flexion contraction of ankle joint and pes cavus deformity were seen. The cerebrospinal fluid protein concentration was elevated. Nerve conduction study showed severe conduction block and temporal dispersion. A sural nerve biopsy revealed remarkable onion bulb-like changes and perivascular infiltration of inflammatory cells. After high-dose corticosteroid treatment, he showed improvement in muscle strength. Although there were no abnormalities of genes related to hereditary neuropathy, the atypical findings of severe demyelinating changes of peripheral nerves mimicked hereditary neuropathy.

Combined use of type A and F botulinum toxins for blepharospasm: a double-blind controlled trial

Type A botulinum toxin has widened its clinical range of applications, but the risk of developing antibodies limits the repeated use of high-dose injection. To minimize the risk, mixing different types of toxin might reduce the antigenic presentation of a specific toxin and associated proteins. At the same time, inhibition of the neuromuscular release process at the multiple sites might potentiate the clinical response or the duration of action. We compared the effectiveness of a mixture of type A and type F botulinum toxins with that of type A or type F toxin alone for treating patients with blepharospasm in a double-blind study. Fifty-four patients had 10 units of toxin injection, a mixture of type A and F toxins (including 5 units of each) on one side and either type A or F toxin on the other side of the orbicularis oculi muscle. Clinical evaluation at 4 and 10 weeks after the injection revealed that the peak clinical effect at 4 weeks was similar among the three preparations. The duration of action of the mixture was intermediate between type A and type F alone, as assessed at 10 weeks, when there was a tendency of conserving the beneficial effect on one eye at the expense of that on the other. Although there was no apparent potentiation of the clinical efficacy, the combination of these different types of toxin might be used for decreasing the risk of antibody development.

Abnormal cortical processing of voluntary muscle relaxation in patients with focal hand dystonia studied by movement-related potentials

In order to clarify the abnormality in cortical motor preparation for voluntary muscle relaxation of the hand in patients with focal hand dystonia, Bereitschaftspotentials (BPs) preceding voluntary muscle contraction and relaxation were recorded in eight patients (three with simple writer's cramp and five with dystonic writer's cramp), and were compared with those from 10 normal subjects. Voluntary muscle relaxation: after keeping the right wrist in an extended position for > 5 s, the subject let the hand drop by voluntarily terminating muscle contraction of the wrist extensor without any associated muscle contraction. Voluntary muscle contraction: the right wrist was flexed by voluntarily contracting the wrist flexor muscle. Scalp EEGs were recorded from 11 electrodes placed over the frontal, central and parietal areas. In the control group, the BP measured at the movement onset was maximal at the left central area (C1), and distributed predominantly over the left hemisphere equally in both the contraction and relaxation tasks. In the focal hand dystonia group, BP was maximal at C1 in the contraction task, whereas, in the relaxation task, it was maximal at the midline central area (Cz) and symmetrically distributed. At the left central area, the BP amplitude in the focal hand dystonia group was diminished significantly in the relaxation task compared with the contraction task (P < 0.05). The present results demonstrate for the first time that the cortical preparatory process for voluntary muscle relaxation, or motor inhibition, is abnormal in focal hand dystonia.

Abnormal contingent negative variation in writer's cramp

OBJECTIVE

To investigate the physiological abnormality in writer's cramp, a focal dystonia which specifically affects writing.

METHODS

We recorded brain potentials that precede hand and neck movements (contingent negative variation or CNV) in 11 patients and 11 age-matched normal subjects. A 1000 Hz tone burst (S1) was delivered to the right or left ear in random sequence, and 2 s after, a 2000 Hz tone burst (S2) was delivered to both ears simultaneously. For the response task to S2, the subjects were instructed to extend their fingers ipsilateral to the ear to which S1 was given in one experiment or to rotate the head to the side of the S1 presentation in another. All the patients had symptoms in the right hand only, and performed both tasks normally. CNV amplitudes were compared between normals and patients using unpaired t test.

RESULTS

They showed normal CNV for neck movement but significantly decreased CNV amplitudes for movements both in the affected and unaffected hands.

CONCLUSIONS

Our findings suggest that motor programming is specifically abnormal for the affected body part, including the asymptomatic contralateral limb, and that the clinical symptom may result from a deficient compensatory mechanism for abnormal motor programs or subroutines.

[The clinical usefulness of high-dose intravenous immunoglobulin therapy for chronic inflammatory demyelinating polyneuropathy and multifocal motor neuropathy]

To explore the optimum dose of intravenous immunoglobulin (i.v.Ig) for treating patients with chronic inflammatory demyelinating polyrneuropathy and multifocal motor neuropathy, we compared the usefulness of i.v.Ig among 3 treatment doses. Fifty-nine patients were randomly divided into three treatment dosage groups: 20 patients for Group I using 50 mg/kg/day x 5 days, 19 patients Group II using 200 mg/kg/day x 5 days, and 20 patients Group III using 400 mg/kg/day x 5 days. We assessed clinically and electrophysiologically the effectiveness of the treatment at 5 weeks after the initial infusion. For patients in Group I and II who had not improved (or worsened) with the first treatment, we gave a one-step larger dose in the second treatment (i.e. 200 mg/kg/day x 5 days for those who had been given 50 mg/kg/day x 5 days, 400 mg/kg/day x 5 days for those who had been given 200 mg/kg/day x 5 days) after more than 9 weeks. We found that 15% of the patients in Group I, 21% in Group II and 60% in Group III improved dose-dependently with the first intravenous immunoglobulin treatment. Seven (47%) of 16 patients in Group I and 4 (40%) of 11 patients in Group II improved after the second treatment with larger doses. Adverse reactions including chill sensation, fever, skin eruption and increase in blood GOT and GPT levels were transient and mild. One patient in Group III developed left hemiparesis showing the small infarction in the right thalamus during the course of the treatment, but the symptom was mild. In conclusion, the high-dose intravenous immunoglobulin therapy (400 mg/kg/day x 5 days) is useful for treating patients with CIDP and MMN, although care must be taken of the risk of causing cerebral infarctions.

Bacterial flagellation and cell division

The peritrichous flagella of Salmonella are synthesized and function through many cell generations. There are two different aspects in the relationship between flagellar biogenesis and cell division. Filament growth is independent from the cell cycle and the length of filaments appear to be locally controlled at each flagellar base, whereas the number of filaments (or flagellar basal bodies) is dependent on cell cycle. We present a model to explain how the number of filaments is maintained through generations. We will also introduce a new direction for research that might directly connect flagellation and cell division; the global communication between flagellar genes and external factors of a complex regulatory network in a cell.