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Inner Membrane Proteins (inner + membrane_protein)

Distribution by Scientific Domains

Life Sciences	83%

Selected Abstracts

Topological analysis and role of the transmembrane domain in polar targeting of PilS, a Pseudomonas aeruginosa sensor kinase

MOLECULAR MICROBIOLOGY, Issue 4 2000
Julie Ethier
In Pseudomonas aeruginosa, synthesis of pilin, the major protein subunit of the pili, is regulated by a two-component signal transduction system in which PilS is the sensor kinase. PilS is an inner membrane protein found at the poles of the bacterial cell. It is composed of three domains: an N-terminal hydrophobic domain; a central cytoplasmic linker region; and the C-terminal transmitter region conserved among other sensor kinases. The signal that activates PilS and, consequently, pilin transcription remains unknown. The membrane topology of the hydrophobic domain was determined using the lacZ and phoA gene fusion approach. In this report, we describe a topological model for PilS in which the hydrophobic domain forms six transmembrane helices, whereas the N- and C-termini are cytoplasmic. This topology is very stable, and the cytoplasmic C-terminus cannot cross the inner membrane. We also show that two of the six transmembrane segments are sufficient for membrane anchoring and polar localization of PilS. [source]

Proteomic analysis of the response of the human neutrophil-like cell line NB-4 after exposure to anthrax lethal toxin

PROTEOMICS - CLINICAL APPLICATIONS, Issue 10 2007
Jun X. Wheeler
Abstract We used 2-D DIGE to analyze the early response of NB-4 cells, a human promyelotic leukemia cell line, exposed to lethal toxin from Bacillus anthracis at the proteome level. After a 2,h exposure, cells were still viable and 43% of spots (n,=,1042) showed a significant change in protein level. We identified 59 spots whose expression had changed significantly, and these reflected cytoskeleton damage, mitochondrial lysis and endoplasmic reticulum stress. Actin filament assembly was disrupted as evidenced by an increase in both actin subunits and phosphorylated cofilin, whilst levels of tropomyosin, tropomodulin and actin related protein 2/3 complex subunit decreased. Lower levels of ATP synthase subunits and mitochondrial inner membrane protein were identified as markers of mitochondrial lysis. Levels of various stress response proteins rose and, uniquely, levels of Ca2+ binding proteins such as translationally controlled tumor protein rose and hippocalcin-like protein 1 decreased. This response may have mitigated effects brought about by mitochondrial lysis and endoplasmic reticulum stress, and delayed or prevented apoptosis in NB-4 cells. These results resemble findings of similar proteomics studies in murine macrophages, although quantitative differences were observed. [source]

VirE2, a Type IV secretion substrate, interacts with the VirD4 transfer protein at cell poles of Agrobacterium tumefaciens

MOLECULAR MICROBIOLOGY, Issue 6 2003
Krishnamohan Atmakuri
Summary Agrobacterium tumefaciens transfers oncogenic DNA and effector proteins to plant cells during the course of infection. Substrate translocation across the bacterial cell envelope is mediated by a type IV secretion (TFS) system composed of the VirB proteins, as well as VirD4, a member of a large family of inner membrane proteins implicated in the coupling of DNA transfer intermediates to the secretion machine. In this study, we demonstrate with novel cytological screens , a two-hybrid (C2H) assay and bimolecular fluorescence complementation (BiFC) , and by immunoprecipitation of chemically cross-linked protein complexes that the VirE2 effector protein interacts directly with the VirD4 coupling protein at cell poles of A. tumefaciens. Analyses of truncation derivatives showed that VirE2 interacts via its C terminus with VirD4, and, further, an NH2 -terminal membrane-spanning domain of VirD4 is dispensable for complex formation. VirE2 interacts with VirD4 independently of the virB -encoded transfer machine and T pilus, the putative periplasmic chaperones AcvB and VirJ, and the T-DNA transfer intermediate. Finally, VirE2 is recruited to polar-localized VirD4 as a complex with its stabilizing secretion chaperone VirE1, yet the effector,coupling protein interaction is not dependent on chaperone binding. Together, our findings establish for the first time that a protein substrate of a type IV secretion system is recruited to a member of the coupling protein superfamily. [source]

A subset of bacterial inner membrane proteins integrated by the twin-arginine translocase

MOLECULAR MICROBIOLOGY, Issue 5 2003
Kostas Hatzixanthis
Summary A group of bacterial exported proteins are synthesized with N-terminal signal peptides containing a SRRxFLK ,twin-arginine' amino acid motif. Proteins bearing twin-arginine signal peptides are targeted post-translationally to the twin-arginine translocation (Tat) system which transports folded substrates across the inner membrane. In Escherichia coli, most integral inner membrane proteins are assembled by a co-translational process directed by SRP/FtsY, the SecYEG translocase, and YidC. In this work we define a novel class of integral membrane proteins assembled by a Tat-dependent mechanism. We show that at least five E. coli Tat substrate proteins contain hydrophobic C-terminal transmembrane helices (or ,C-tails'). Fusions between the identified transmembrane C-tails and the exclusively Tat-dependent reporter proteins TorA and SufI render the resultant chimeras membrane-bound. Export-linked signal peptide processing and membrane integration of the chimeras is shown to be both Tat-dependent and YidC-independent. It is proposed that the mechanism of membrane integration of proteins by the Tat system is fundamentally distinct from that employed for other bacterial inner membrane proteins. [source]

Fishing new proteins in the twilight zone of genomes: The test case of outer membrane proteins in Escherichia coli K12, Escherichia coli O157:H7, and other Gram-negative bacteria

PROTEIN SCIENCE, Issue 6 2003
Rita Casadio
Abstract We address the problem of clustering the whole protein content of genomes into three different categories,globular, all-,, and all-, membrane proteins,with the aim of fishing new membrane proteins in the pool of nonannotated proteins (twilight zone). The focus is then mainly on outer membrane proteins. This is performed by using an integrated suite of programs (Hunter) specifically developed for predicting the occurrence of signal peptides in proteins of Gram-negative bacteria and the topography of all-, and all-, membrane proteins. Hunter is tested on the well and partially annotated proteins (2160 and 760, respectively) of Escherichia coli K 12 scoring as high as 95.6% in the correct assignment of each chain to the category. Of the remaining 1253 nonannotated sequences, 1099 are predicted globular, 136 are all-,, and 18 are all-, membrane proteins. In Escherichia coli 0157:H7 we filtered 1901 nonannotated proteins. Our analysis classifies 1564 globular chains, 327 inner membrane proteins, and 10 outer membrane proteins. With Hunter, new membrane proteins are added to the list of putative membrane proteins of Gram-negative bacteria. The content of outer membrane proteins per genome (nine are analyzed) ranges from 1.5% to 2.4%, and it is one order of magnitude lower than that of inner membrane proteins. The finding is particularly relevant when it is considered that this is the first large-scale analysis based on validated tools that can predict the content of outer membrane proteins in a genome and can allow cross-comparison of the same protein type between different species. [source]