Matsuyama S, Fujita Y, Mizushima S
Institute of Applied Microbiology, University of Tokyo, Japan.
EMBO J. 1993 Jan;12(1):265-70. doi: 10.1002/j.1460-2075.1993.tb05652.x.
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.
SecD蛋白是基因研究中提出的参与大肠杆菌细胞质膜蛋白分泌的成分之一。我们使用原生质球研究了抗SecD IgG对蛋白分泌的影响。观察到该IgG抑制了OmpA和麦芽糖结合蛋白（MBP）的分泌，同时其前体和成熟形式在原生质球中积累。这种作用对抗SecD IgG具有特异性。抗SecE和抗SecY IgG的表位分别位于SecE和SecY的周质结构域，它们不干扰分泌。研究原MBP加工过程和MBP从原生质球释放的时间进程实验表明，抗SecD IgG干扰了易位成熟MBP的释放。如此积累的MBP成熟形式对添加到原生质球外部的胰蛋白酶敏感，而释放到培养基中的MBP对胰蛋白酶具有抗性，如同天然MBP一样。在原生质球中积累的MBP前体形式也对胰蛋白酶具有抗性。我们得出结论，SecD直接参与蛋白分泌，并且对于已跨细胞质膜易位的蛋白的释放很重要。
