Topology of the integral membrane form of Escherichia coli SecA protein reveals multiple periplasmically exposed regions and modulation by ATP binding - PubMed (original) (raw)

. 1997 Sep 12;272(37):23239-46.

doi: 10.1074/jbc.272.37.23239.

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Topology of the integral membrane form of Escherichia coli SecA protein reveals multiple periplasmically exposed regions and modulation by ATP binding

V Ramamurthy et al. J Biol Chem. 1997.

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Abstract

SecA insertion and integration into the Escherichia coli inner membrane is a critical step for the catalysis of protein translocation across this layer. To understand this step further, SecA topology was investigated. To determine which regions of SecA are periplasmically exposed, right-side out membrane vesicles were prepared from strains synthesizing monocysteine SecA variants produced by mutagenesis and probed with a membrane-impermeant sulfhydryl-labeling reagent. To determine which regions of SecA contain membrane-integration determinants, inverted inner membrane vesicles were subjected to proteolysis, and integral-membrane fragments of SecA were identified with region-specific antibodies. The membrane association properties of various truncated SecA species produced in vivo were also determined. Our analysis indicates that the membrane topology of SecA is complex with amino-terminal, central, and carboxyl-terminal regions of SecA integrated into the membrane where portions are periplasmically accessible. Furthermore, the insertion and penetration of the amino-terminal third of SecA, which includes the proposed preprotein-binding domain, is subject to modulation by ATP binding. The importance of these studies to the cycle of membrane insertion and de-insertion of SecA that promotes protein translocation and SecA's proximity to the preprotein channel are discussed.

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