Secretins form large multimeric pores in the outer membrane (OM) of Gram-negative bacteria. These pores are part of type II and III secretion systems (T2SS and T3SS, respectively) and are crucial for ...pathogenicity. Recent structural studies indicate that secretins form a structure rich in β-strands. However, little is known about the mechanism by which secretins assemble into the OM. Based on the conservation of the biogenesis of β-barrel proteins in bacteria and mitochondria, we used yeast cells as a model system to study the assembly process of secretins. To that end, we analyzed the biogenesis of PulD (T2SS), SsaC (T3SS) and InvG (T3SS) in wild type cells or in cells mutated for known mitochondrial import and assembly factors. Our results suggest that secretins can be expressed in yeast cells, where they are enriched in the mitochondrial fraction. Interestingly, deletion of mitochondrial import receptors like Tom20 and Tom70 reduces the mitochondrial association of PulD but does not affect that of InvG. SsaC shows another dependency pattern and its membrane assembly is enhanced by the absence of Tom70 and compromised in cells lacking Tom20 or the topogenesis of outer membrane β-barrel proteins (TOB) complex component, Mas37. Collectively, these findings suggest that various secretins can follow different pathways to assemble into the bacterial OM.
Thus far, the role of the Escherichia coli signal recognition particle (SRP) has only been studied using targeted approaches. It has been shown for a handful of cytoplasmic membrane proteins that ...their insertion into the cytoplasmic membrane is at least partially SRP-dependent. Furthermore, it has been proposed that the SRP plays a role in preventing toxic accumulation of mistargeted cytoplasmic membrane proteins in the cytoplasm. To complement the targeted studies on SRP, we have studied the consequences of the depletion of the SRP component Fifty-four homologue (Ffh) in E. coli using a global approach. The steady-state proteomes and the proteome dynamics were evaluated using one- and two-dimensional gel analysis, followed by mass spectrometry-based protein identification and immunoblotting. Our analysis showed that depletion of Ffh led to the following: (i) impaired kinetics of the biogenesis of the cytoplasmic membrane proteome; (ii) lowered steady-state levels of the respiratory complexes NADH dehydrogenase, succinate dehydrogenase, and cytochrome bo3 oxidase and lowered oxygen consumption rates; (iii) increased levels of the chaperones DnaK and GroEL at the cytoplasmic membrane; (iv) a σ32 stress response and protein aggregation in the cytoplasm; and (v) impaired protein synthesis. Our study shows that in E. coli SRP-mediated protein targeting is directly linked to maintaining protein homeostasis and the general fitness of the cell.
Virulence-associated bacterial type III secretion systems are multiprotein molecular machines that promote the pathogenicity of bacteria towards eukaryotic host cells. These machines form needle-like ...structures, named injectisomes, that span both bacterial and host membranes, forming a direct conduit for the delivery of bacterial proteins into host cells. Once within the host, these bacterial effector proteins are capable of manipulating a multitude of host cell functions. In recent years, the knowledge of assembly, structure and function of these machines has grown substantially and is presented and discussed in this review.
The mechanisms underlying discrimination between "self" and "non-self", a central immunological principle, require careful consideration in immune oncology therapeutics where eliciting anti-cancer ...immunity must be weighed against the risk of autoimmunity due to the self origin of tumors. Whole cell vaccines are one promising immunotherapeutic avenue whereby a myriad of tumor antigens are introduced in an immunogenic context with the aim of eliciting tumor rejection. Despite the possibility collateral damage to healthy tissues, cancer immunotherapy can be designed such that off target autoimmunity remains limited in scope and severity or completely non-existent. Here we provide an immunological basis for reconciling the safety of cancer vaccines, focusing on tumor endothelial cell vaccines, by discussing the following topics: (a) Antigenic differences between neoplastic and healthy tissues that can be leveraged in cancer vaccine design; (b) The layers of tolerance that control T cell responses directed against antigens expressed in healthy tissues and tumors; and, (c) The hierarchy of antigenic epitope selection and display in response to whole cell vaccines, and how antigen processing and presentation can afford a degree of selectivity against tumors. We conclude with an example of early clinical data utilizing ValloVax™, an immunogenic placental endothelial cell vaccine that is being advanced to target the tumor endothelium of diverse cancers, and we report on the safety and efficacy of ValloVax™ for inducing immunity against tumor endothelial antigens.
The polytopic inner membrane protein MalF is a constituent of the MalFGK2 maltose transport complex in Escherichia coli. We have studied the biogenesis of MalF using a combination of in vivo and in ...vitro approaches. MalF is targeted via the SRP pathway to the Sec/YidC insertion site. Despite close proximity of nascent MalF to YidC during insertion, YidC is not required for the insertion of MalF into the membrane. However, YidC is required for the stability of MalF and the formation of the MalFGK2 maltose transport complex. Our data indicate that YidC supports the folding of MalF into a stable conformation before it is incorporated into the maltose transport complex.
The self-sufficient autotransporter (AT) pathway, ubiquitous in Gram-negative bacteria, combines a relatively simple protein secretion mechanism with a high transport capacity. ATs consist of a ...secreted passenger domain and a β-domain that facilitates transfer of the passenger across the cell-envelope. They have a great potential for the extracellular expression of recombinant proteins but their exploitation has suffered from the limited structural knowledge of carrier ATs. Capitalizing on its crystal structure, we have engineered the Escherichia coli AT Hemoglobin protease (Hbp) into a platform for the secretion and surface display of heterologous proteins, using the Mycobacterium tuberculosis vaccine target ESAT6 as a model protein.
Based on the Hbp crystal structure, five passenger side domains were selected and one by one replaced by ESAT6, whereas a β-helical core structure (β-stem) was left intact. The resulting Hbp-ESAT6 chimeras were efficiently and stably secreted into the culture medium of E. coli. On the other hand, Hbp-ESAT6 fusions containing a truncated β-stem appeared unstable after translocation, demonstrating the importance of an intact β-stem. By interrupting the cleavage site between passenger and β-domain, Hbp-ESAT6 display variants were constructed that remain cell associated and facilitate efficient surface exposure of ESAT6 as judged by proteinase K accessibility and whole cell immuno-EM analysis. Upon replacement of the passenger side domain of an alternative AT, EspC, ESAT6 was also efficiently secreted, showing the approach is more generally applicable to ATs. Furthermore, Hbp-ESAT6 was efficiently displayed in an attenuated Salmonella typhimurium strain upon chromosomal integration of a single encoding gene copy, demonstrating the potential of the Hbp platform for live vaccine development.
We developed the first structurally informed AT platform for efficient secretion and surface display of heterologous proteins. The platform has potential with regard to the development of recombinant live vaccines and may be useful for other biotechnological applications that require high-level secretion or display of recombinant proteins by bacteria.
To improve understanding and identify novel substrates of the cytoplasmic chaperone SecB in Escherichia coli, we analyzed a secB null mutant using comparative proteomics. The secB null mutation did ...not affect cell growth but caused significant differences at the proteome level. In the absence of SecB, dynamic protein aggregates containing predominantly secretory proteins accumulated in the cytoplasm. Unprocessed secretory proteins were detected in radiolabeled whole cell lysates. Furthermore, the assembly of a large fraction of the outer membrane proteome was slowed down, whereas its steady state composition was hardly affected. In response to aggregation and delayed sorting of secretory proteins, cytoplasmic chaperones DnaK, GroEL/ES, ClpB, IbpA/B, and HslU were up-regulated severalfold, most likely to stabilize secretory proteins during their delayed translocation and/or rescue aggregated secretory proteins. The SecB/A dependence of 12 secretory proteins affected by the secB null mutation (DegP, FhuA, FkpA, OmpT, OmpX, OppA, TolB, TolC, YbgF, YcgK, YgiW, and YncE) was confirmed by “classical” pulse-labeling experiments. Our study more than triples the number of known SecB-dependent secretory proteins and shows that the primary role of SecB is to facilitate the targeting of secretory proteins to the Sec-translocase.
Use of atypical antipsychotics (AA) in combination with an antidepressant is recommended as an augmentation strategy for patients with depression. However, there is a paucity of data comparing ...aripiprazole and other AAs in terms of patient reported outcomes. Therefore, the objective of this study was to examine the levels of HRQoL and health utility scores in patients with depression using aripiprazole compared with patients using olanzapine, quetiapine, risperidone and ziprasidone.
Data were obtained from the 2009, 2010, and 2011 National Health and Wellness Survey (NHWS), a cross-sectional, internet-based survey that is representative of the adult US population. Only those patients who reported being diagnosed with depression and taking an antidepressant and an atypical antipsychotic for depression were included. Patients taking an atypical antipsychotic for less than 2 months or who reported being diagnosed with bipolar disorder or schizophrenia were excluded. Patients taking aripiprazole were compared with patients taking other atypical antipsychotics. Health-related quality of life (HRQoL) and health utilities were assessed using the Short Form 12-item (SF-12) health survey. Differences between groups were analyzed using General Linear Models (GLM) controlling for demographic and health characteristics.
Overall sample size was 426 with 59.9% taking aripiprazole (n=255) and 40.1% (n=171) taking another atypical antipsychotic (olanzapine (n=19), quetiapine (n=127), risperidone (n=14) or ziprasidone (n=11)). Of the SF-12 domains, mean mental component summary (MCS) score (p=.018), bodily pain (p=.047), general health (p=.009) and emotional role limitations (p=.009) were found to be significantly higher in aripiprazole users indicating better HRQoL compared to other atypical antipsychotics. After controlling for demographic and health characteristics, patients taking aripiprazole reported significantly higher mean mental SF-12 component summary (34.10 vs. 31.43, p=.018), bodily pain (55.19 vs. 49.05, p=.047), general health (50.05 vs. 43.07, p=.009), emotional role limitations (49.44 vs. 41.83, p=.009), and SF-6D utility scores (0.59 vs. 0.56, p=.042).
Comparison of patients taking aripiprazole with a cohort of patients using another AA for depression demonstrated that aripiprazole was independently associated with better (both statistically and clinically) HRQoL and health utilities.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Virulence-associated type III secretion systems (T3SS) serve the injection of bacterial effector proteins into eukaryotic host cells. They are able to secrete a great diversity of substrate proteins ...in order to modulate host cell function, and have evolved to sense host cell contact and to inject their substrates through a translocon pore in the host cell membrane. T3SS substrates contain an N-terminal signal sequence and often a chaperone-binding domain for cognate T3SS chaperones. These signals guide the substrates to the machine where substrates are unfolded and handed over to the secretion channel formed by the transmembrane domains of the export apparatus components and by the needle filament. Secretion itself is driven by the proton motive force across the bacterial inner membrane. The needle filament measures 20-150 nm in length and is crowned by a needle tip that mediates host-cell sensing. Secretion through T3SS is a highly regulated process with early, intermediate and late substrates. A strict secretion hierarchy is required to build an injectisome capable of reaching, sensing and penetrating the host cell membrane, before host cell-acting effector proteins are deployed. Here, we review the recent progress on elucidating the assembly, structure and function of T3SS injectisomes.
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