The Lol system, comprising five Lol proteins, transfers lipoproteins from the inner to the outer membrane of Escherichia coli. Periplasmic LolA accepts lipoproteins from LolCDE in the inner membrane and immediately transfers them to LolB, a receptor anchored to the outer membrane. The unclosed ␤-barrel structures of LolA and LolB are very similar to each other and form hydrophobic cavities for lipoproteins. The lipoprotein transfer between these similar structures is unidirectional and very efficient, but requires no energy input. To reveal the mechanisms underlying this lipoprotein transfer, Arg and Phe at positions 43 and 47, respectively, of LolA were systematically mutagenized. The two residues were previously found to affect abilities to accept and transfer lipoproteins. Substitution of Phe-47 with polar residues inhibited the ability to accept lipoproteins from the inner membrane. No derivatives caused periplasmic accumulation of lipoproteins. In contrast, many Arg-43 derivatives caused unusual periplasmic accumulation of lipoproteins to various extents. However, all derivatives, except one having Leu instead of Arg, supported the growth of cells. All Arg-43 derivatives retained the ability to accept lipoproteins from the inner membrane, whereas their abilities to transfer associated lipoproteins to LolB were variously reduced. Assessment of the intensity of the hydrophobic interaction between lipoproteins and Arg-43 derivatives revealed that the LolA-lipoprotein interaction should be weak, otherwise lipoprotein transfer to LolB is inhibited, causing accumulation of lipoproteins in the periplasm.Bacterial lipoproteins are synthesized as precursors and then translocated to the periplasmic side of the inner membrane, where they are processed to mature forms (1, 2). Mature lipoproteins have an N-terminal Cys that is modified by thioether-linked diacylglycerol and aminolinked acyl chains (3). Escherichia coli has at least 90 lipoproteins (4 -6), which are anchored through N-terminal lipids to the periplasmic leaflet of either the inner or outer membrane depending on the sorting signal. When lipoproteins have Asp at position 2 (7), they are retained in the inner membrane, presumably through an interaction between Asp at position 2 and phospholipids (8). Residues other than Asp at position 2 cause outer membrane localization of lipoproteins (9, 10).The Lol system, comprising five Lol proteins, is required for the sorting and outer membrane localization of lipoproteins. The LolCDE complex, an ATP binding cassette transporter, releases outer membranedirected lipoproteins from the inner membrane in an ATP-dependent manner (11, 12), leading to the formation of a water-soluble complex comprising one molecule each of a lipoprotein and LolA in the periplasm (13, 14). Interaction of the LolA-lipoprotein complex with outer membrane receptor LolB induces the energy-independent transfer of lipoproteins from LolA to LolB, and then from LolB to the outer membrane (15,16). LolB is itself a lipoprotein anchored to the outer me...

SummaryThe LolCDE complex of Escherichia coli belongs to the ABC transporter superfamily and initiates the lipoprotein sorting to the outer membrane by catalysing their release from the inner membrane. LolC and/or LolE, membrane subunits, recognize lipoproteins anchored to the outer surface of the inner membrane, while LolD hydrolyses ATP on its inner surface. We report here that ligand-bound LolCDE can be purified from the inner membrane in the absence of ATP.

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The changes in vortical and turbulent structure in the near field (X/D < 3.0) of jet mixing flow caused by a lobed nozzle were investigated experimentally in the present study. The techniques of planar laser induced fluorescence and particle image velocimetry were used to accomplish flow visualization and velocity field measurements. The experimental results showed that, compared with a circular jet flow, lobed jet mixing flow was found to have a shorter laminar region, a smaller scale of the spanwise Kelvin-Helmholtz vortices, earlier appearance of small scale turbulent structures and a larger region of intensive mixing in the near field of the jet mixing flow. The central line velocity decay of the lobed jet mixing flow was also found to be much faster than that in a conventional circular jet. All these indicated that the lobed nozzle provides better mixing performance than does a conventional circular nozzle.

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The C-terminal domain of subunit of the bacterial F o F 1 ATP synthase is reported to be an intrinsic inhibitor of ATP synthesis/hydrolysis activity in vitro, preventing wasteful hydrolysis of ATP under low-energy conditions. Mutants defective in this regulatory domain exhibited no significant difference in growth rate, molar growth yield, membrane potential, or intracellular ATP concentration under a wide range of growth conditions and stressors compared to wild-type cells, suggesting this inhibitory domain is dispensable for growth and survival of Escherichia coli.