Radioisotope Center, University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
J Bacteriol. 2010 Nov;192(21):5657-62. doi: 10.1128/JB.00821-10. Epub 2010 Aug 27.
LolA accommodates the acyl chains of lipoproteins in its hydrophobic cavity and shuttles between the inner and outer membranes through the hydrophilic periplasm to place lipoproteins in the outer membrane. The LolA(I93C/F140C) derivative, in which Cys replaces Ile at position 93 and Phe at position 140, strongly inhibited growth in the absence of a reducing agent because of the lethal intramolecular disulfide bond between the two Cys residues. Expression of I93C/F140C was found to activate the Cpx two-component system, which responds to cell envelope stress. The inhibition of growth by I93C/F140C was partly suppressed by overproduction of LolCDE, which is an ATP-binding cassette transporter and mediates the transfer of lipoproteins from the inner membrane to LolA. A substantial portion of the oxidized form, but not the reduced one, of I93C/F140C expressed on LolCDE overproduction was recovered in the membrane fraction, whereas wild-type LolA was localized in the periplasm even when LolCDE was overproduced. Moreover, LolCDE overproduction stabilized I93C/F140C and therefore caused an increase in its level. Taken together, these results indicate that oxidized I93C/F140C stably binds to LolCDE, which causes strong envelope stress.
LolA 在其疏水性腔中容纳脂蛋白的酰基链，并通过亲水性周质在内外膜之间穿梭，将脂蛋白放置在外膜中。LolA（I93C/F140C）衍生物中，Cys 取代了位置 93 的 Ile 和位置 140 的 Phe，由于两个 Cys 残基之间的致命分子内二硫键，在没有还原剂的情况下强烈抑制生长。发现 I93C/F140C 的表达激活了 Cpx 双组分系统，该系统对细胞包膜应激作出反应。I93C/F140C 的生长抑制作用部分被 LolCDE 的过度表达所抑制，LolCDE 是一种 ATP 结合盒转运蛋白，介导脂蛋白从内膜转移到 LolA。大量的氧化形式，而不是还原形式，在 LolCDE 过度表达时表达的 I93C/F140C 被回收在膜部分，而野生型 LolA 即使在 LolCDE 过度表达时也定位于周质。此外，LolCDE 的过度表达稳定了 I93C/F140C，因此增加了其水平。总之，这些结果表明，氧化的 I93C/F140C 稳定地结合到 LolCDE，这导致强烈的 envelope stress。
