outer membrane protein
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2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Yue Li ◽  
Wanqing Zheng ◽  
Yangyang Lu ◽  
Yanrong Zheng ◽  
Ling Pan ◽  
...  

AbstractMitophagy is a highly conserved cellular process that maintains the mitochondrial quantity by eliminating dysfunctional or superfluous mitochondria through autophagy machinery. The mitochondrial outer membrane protein BNIP3L/Nix serves as a mitophagy receptor by recognizing autophagosomes. BNIP3L is initially known to clear the mitochondria during the development of reticulocytes. Recent studies indicated it also engages in a variety of physiological and pathological processes. In this review, we provide an overview of how BNIP3L induces mitophagy and discuss the biological functions of BNIP3L and its regulation at the molecular level. We further discuss current evidence indicating the involvement of BNIP3L-mediated mitophagy in human disease, particularly in cancer and neurological disorders.


Author(s):  
Tobias Beer ◽  
Sebastian Hänsch ◽  
Klaus Pfeffer ◽  
Sander H.J. Smits ◽  
Stefanie Weidtkamp-Peters ◽  
...  

Secretion systems are essential for Gram-negative bacteria as these nanomachineries allow a communication with the outside world by exporting proteins into the extracellular space or directly into the cytosol of a host cell. For example, type one secretion systems (T1SS) secrete a broad range of substrates across both membranes into the extracellular space. One well-known example is the hemolysin A (HlyA) T1SS from Escherichia coli (E. coli) , which consists of an ABC transporter (HlyB), a membrane fusion protein (HlyD), the outer membrane protein TolC and the substrate HlyA, a member of the family of RTX (repeats in toxins) toxins. Here, we determined the amount of TolC at the endogenous level (parental strain, UTI89) and under conditions of overexpression (T7 expression system, BL21(DE3)-BD). The overall amount of TolC was not influenced by the overexpression of the HlyBD complex. Moving one step further, we determined the localization of the HlyA T1SS by super-resolution microscopy. In contrast to other bacterial secretion systems, no polarization was observed with respect to endogenous or overexpression levels. Additionally, the cell growth and division cycle did not influence the polarization. Most importantly, the size of the observed T1SS clusters did not correlate with the recently proposed outer membrane islands. These data indicate that T1SS cluster at the outer membrane generating domains of so far not described identity. Importance Uropathogenic Escherichia coli (UPEC) strains cause about 110 million urinary tract infections each year worldwide representing a global burden to the healthcare system. UPEC secrete many virulence factors among these the TX toxin hemolysin A via a cognate T1SS into the extracellular space. In this study, we determined the endogenous copy number of the HlyA T1SS in UTI89 and analyzed the surface localization in BL21(DE3)-BD and UTI89, respectively. With approximately 800 copies of the T1SS in UTI89, this is one of the highest expressed bacterial secretion systems. Furthermore and in clear contrast to other secretion systems, no polarized surface localization was detected. Finally, quantitative analysis of the super-resolution data revealed that clusters of the HlyA T1SS are not related to the recently identified outer membrane protein islands. These data provide insights into the quantitative molecular architecture of the HlyA T1SS.


Author(s):  
Junaida M. Ibrahim ◽  
Shanitha A. ◽  
Achuthsankar S. Nair ◽  
Oommen V. Oommen ◽  
Perumana R. Sudhakaran

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
David Pajuelo ◽  
Uday Tak ◽  
Lei Zhang ◽  
Olga Danilchanka ◽  
Anna D. Tischler ◽  
...  

AbstractThe tuberculosis necrotizing toxin (TNT) is the major cytotoxicity factor of Mycobacterium tuberculosis (Mtb) in macrophages. TNT is the C-terminal domain of the outer membrane protein CpnT and gains access to the cytosol to kill macrophages infected with Mtb. However, molecular mechanisms of TNT secretion and trafficking are largely unknown. A comprehensive analysis of the five type VII secretion systems of Mtb revealed that the ESX-4 system is required for export of CpnT and surface accessibility of TNT. Furthermore, the ESX-2 and ESX-4 systems are required for permeabilization of the phagosomal membrane in addition to the ESX-1 system. Thus, these three ESX systems need to act in concert to enable trafficking of TNT into the cytosol of Mtb-infected macrophages. These discoveries establish new molecular roles for the two previously uncharacterized type VII secretion systems ESX-2 and ESX-4 and reveal an intricate link between toxin secretion and phagosomal permeabilization by Mtb.


2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Zehui Yang ◽  
Yingying Chen ◽  
Qiang Zhang ◽  
Xiaodong Chen ◽  
Ze Deng

Legionella pneumophila is an intracellular pathogen that can cause Legionnaire’s disease by invading alveolar epithelial cells and macrophages. The major outer membrane protein (MOMP) plays an important role in the interaction between bacteria and host cells. However, the role of MOMP in the process of L. pneumophila invasion of macrophages and its working mechanism remain unknown. We aimed to explore the effects of MOMP on phagocytosis and chemotaxis of RAW 264.7 macrophages. The chemotactic activity, toxicity, and phagocytosis of RAW 264.7 cocultured with different concentrations of MOMP were determined by Transwell, CCK-8, and neutral red uptake assays, respectively. Target genes were detected by double-luciferase and pull down assays. qRT-PCR and Western blot were performed to analyze the expression of several important proteins involved in the immune response pathway, including coronin-1, interleukins (IL-10), forkhead transcription factor 1 (FOXO1), nucleotide-binding oligomerization domain protein (NOD) 1, NOD2, and receptor-interacting protein (RIP) 2. After coculturing with MOMP, cytological observation indicated a decrease of phagocytosis and a marked increase of chemotaxis in RAW 264.7 macrophages. The phagocytosis degree of RAW 264.7 macrophage varied with the concentration gradient of MOMP in a time-dependent manner. MOMP could increase the expression levels of MCP-1, IL-10, NOD2, and RIP2 and decrease the expression levels of FOXO1 and coronin-1 in cell culture supernatants. In addition, we found that FOXO1 could promote its transcription by binding to the promoter of coronin-1. The results of the present study suggested that MOMP could inhibit phagocytosis and facilitate chemotaxis of RAW 264.7 macrophage, which might be associated with the FOXO1/coronin-1 axis.


2021 ◽  
Vol 9 (11) ◽  
pp. 2338
Author(s):  
Jianxin Gao ◽  
Zhonghui Han ◽  
Ping Li ◽  
Hongyan Zhang ◽  
Xinjun Du ◽  
...  

In some Gram-negative bacteria, ompF encodes outer membrane protein F (OmpF), which is a cation-selective porin and is responsible for the passive transport of small molecules across the outer membrane. However, there are few reports about the functions of this gene in Cronobacter sakazakii. To investigate the role of ompF in detail, an ompF disruption strain (ΔompF) and a complementation strain (cpompF) were successfully obtained. We find that OmpF can affect the ability of biofilm formation in C. sakazakii. In addition, the variations in biofilm composition of C. sakazakii were examined using Raman spectroscopy analyses caused by knocking out ompF, and the result indicated that the levels of certain biofilm components, including lipopolysaccharide (LPS), were significantly decreased in the mutant (ΔompF). Then, SDS-PAGE was used to further analyze the LPS content, and the result showed that the LPS levels were significantly reduced in the absence of ompF. Therefore, we conclude that OmpF affects biofilm formation in C. sakazakii by reducing the amount of LPS. Furthermore, the ΔompF mutant showed decreased (2.7-fold) adhesion to and invasion of HCT-8 cells. In an antibiotic susceptibility analysis, the ΔompF mutant showed significantly smaller inhibition zones than the WT, indicating that OmpF had a positive effect on the influx of antibiotics into the cells. In summary, ompF plays a positive regulatory role in the biofilm formation and adhesion/invasion, which is achieved by regulating the amount of LPS, but is a negative regulator of antibiotic resistance in C. sakazakii.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jacob Tickner ◽  
Sophia Hawas ◽  
Makrina Totsika ◽  
Johanna J. Kenyon

AbstractIdentification of novel therapeutic targets is required for developing alternate strategies to treat infections caused by the extensively drug-resistant bacterial pathogen, Acinetobacter baumannii. As capsular polysaccharide (CPS) is a prime virulence determinant required for evasion of host immune defenses, understanding the pathways for synthesis and assembly of this discrete cell-surface barrier is important. In this study, we assess cell-bound and cell-free CPS material from A. baumannii AB5075 wildtype and transposon library mutants and demonstrate that the Wzi outer membrane protein is required for the proper assembly of the CPS layer on the cell surface. Loss of Wzi resulted in an estimated 4.4-fold reduction in cell-associated CPS with a reciprocal increase in CPS material shed in the extracellular surrounds. Transmission electron microscopy revealed a disrupted CPS layer with sparse patches of CPS on the external face of the outer membrane when Wzi function was lost. However, this genotype did not have a significant effect on biofilm formation. Genetic analysis demonstrated that the wzi gene is ubiquitous in the species, though the nucleotide sequences were surprisingly diverse. Though divergence was not concomitant with variation at the CPS biosynthesis K locus, an association between wzi type and the first sugar of the CPS representing the base of the structure most likely to interact with Wzi was observed.


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