SecD is involved in the release of translocated secretory proteins from the cytoplasmic membrane of Escherichia coli.
The SecD protein is one of the components that has been suggested from genetic studies to be involved in the protein secretion across the cytoplasmic membrane of Escherichia coli. We examined the effect of anti-SecD IgG on protein secretion using spheroplasts. Inhibition of the secretion of OmpA and maltose-binding protein (MBP) by this IgG was observed with concomitant accumulation of their precursor and mature forms in spheroplasts. This effect was specific to anti-SecD IgG. Anti-SecE and anti-SecY IgGs, of which the epitopes are located at the periplasmic domains of SecE and SecY, respectively, did not interfere with the secretion. Time-course experiments investigating the processing of proMBP and the release of MBP from spheroplasts revealed that anti-SecD IgG interfered with the release of the translocated mature MBP. The mature form of MBP thus accumulated was sensitive to trypsin, which was externally added to spheroplasts, whereas MBP released into the medium was resistant to trypsin as the native MBP is. The precursor form of MBP accumulated in spheroplasts was also trypsin resistant. We conclude that SecD is directly involved in protein secretion and important for the release of proteins that have been translocated across the cytoplasmic membrane.
Matsuyama
S
S
Institute of Applied Microbiology, University of Tokyo, Japan.
Fujita
Y
Y
Mizushima
S
S
D018528:ATP-Binding Cassette Transporters; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D007700:Kinetics; D008320:Maltose; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D013104:Spheroplasts / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D011498:Protein Precursors; C499394:SecD protein, E coli; C461599:maltose transport system, E coli; C075767:secD protein, Bacteria; D008320:Maltose