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Preserving the membrane barrier for small molecules during bacterial protein translocation.

ABSTRACT: Many proteins are translocated through the SecY channel in bacteria and archaea and through the related Sec61 channel in eukaryotes. The channel has an hourglass shape with a narrow constriction approximately halfway across the membrane, formed by a pore ring of amino acids. While the cytoplasmic cavity of the channel is empty, the extracellular cavity is filled with a short helix called the plug, which moves out of the way during protein translocation. The mechanism by which the channel transports large polypeptides and yet prevents the passage of small molecules, such as ions or metabolites, has been controversial. Here, we have addressed this issue in intact Escherichia coli cells by testing the permeation of small molecules through wild-type and mutant SecY channels, which are either in the resting state or contain a defined translocating polypeptide chain. We show that in the resting state, the channel is sealed by both the pore ring and the plug domain. During translocation, the pore ring forms a 'gasket-like' seal around the polypeptide chain, preventing the permeation of small molecules. The structural conservation of the channel in all organisms indicates that this may be a universal mechanism by which the membrane barrier is maintained during protein translocation.

SUBMITTER: Park E

PROVIDER: S-EPMC3093665 | biostudies-literature | 2011 May

REPOSITORIES: biostudies-literature

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Preserving the membrane barrier for small molecules during bacterial protein translocation.

Park Eunyong E Rapoport Tom A TA

Nature 20110501 7346

Many proteins are translocated through the SecY channel in bacteria and archaea and through the related Sec61 channel in eukaryotes. The channel has an hourglass shape with a narrow constriction approximately halfway across the membrane, formed by a pore ring of amino acids. While the cytoplasmic cavity of the channel is empty, the extracellular cavity is filled with a short helix called the plug, which moves out of the way during protein translocation. The mechanism by which the channel transpo ...[more]

PMID: 21562565

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Project description:BACKGROUND: Although clinical and experimental studies have demonstrated a correlation between obstructive jaundice and the development of sepsis, the mechanism has not been fully elucidated. PURPOSE: The aim of this study was to investigate the influence of biliary obstruction on bacterial translocation as a possible source of infection in cases of obstructive jaundice. MATERIAL AND METHODS: Two groups of 12 Wistar rats were examined: rats subjected to common bile duct (CBD) ligation (group A) and rats subjected to a sham operation (group B). After 7 days, blood samples were taken and liver, spleen, and mesenteric lymph nodes (MLNs) from the ileocecal area were removed, divided into small pieces, and cultured. Quantitative culture results were determined by the number of colony-forming units (CFU) per milliliter of homogenate. Bacterial translocation was defined as the presence of a positive culture of MLNs, blood, liver, and/or spleen. Samples for histopathological examination were taken from the mucosa of the ileum and the colon and evaluated for inflammatory and destructive changes. RESULTS: There was no evidence of bacterial translocation to MLNs, blood, spleen, or liver detected in any of the 12 sham-operated control rats. In contrast, bacterial translocation was demonstrated in 8 of the 12 CBD-ligated rats (P < 0.01). In all eight cases in which translocation occurred, Escherichia coli were cultured from the MLNs. There were no histological changes in the mucosal samples of the control animals. In the CBD-ligated rats, hyperemia, vacuolization, reduction of goblet cells, decreased mitotic activity, and infiltration by lymphocytes and polymorphonuclear leukocytes (PMNLs) were detected. Cases in which translocation occurred were significantly associated with decreased mitotic activity in the colon (r = -0.5, P < 0.01) and higher infiltration by PMNLs in the ileum (r = -0.62, P < 0.05). CONCLUSION: Obstructive jaundice in a rat model predisposes to bacterial translocation. This suggests a mechanism whereby jaundiced patients are susceptible to septic complication.

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Preserving the membrane barrier for small molecules during bacterial protein translocation.

Publications

Preserving the membrane barrier for small molecules during bacterial protein translocation.

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