Abstract
The mechanisms by which lipid bilayer properties govern or influence membrane protein functions are little understood, but a liquid-crystalline state and the presence of anionic and nonbilayer (NB)-prone lipids seem important. An Escherichia coli mutant lacking the major membrane lipid phosphatidylethanolamine (NB-prone) requires divalent cations for viability and cell integrity and is impaired in several membrane functions that are corrected by introduction of the "foreign" NB-prone neutral glycolipid alpha-monoglucosyldiacylglycerol (MGlcDAG) synthesized by the MGlcDAG synthase from Acholeplasma laidlawii. Dependence on Mg(2+) was reduced, and cellular yields and division malfunction were greatly improved. The increased passive membrane permeability of the mutant was not abolished, but protein-mediated osmotic stress adaptation to salts and sucrose was recovered by the presence of MGlcDAG. MGlcDAG also restored tryptophan prototrophy and active transport function of lactose permease, both critically dependent on phosphatidylethanolamine. Three mechanisms can explain the observed effects: NB-prone MGlcDAG improves the quenched lateral pressure profile across the bilayer; neutral MGlcDAG dilutes the high anionic lipid surface charge; MGlcDAG provides a neutral lipid that can hydrogen bond and/or partially ionize. The reduced dependence on Mg(2+) and lack of correction by high monovalent salts strongly support the essential nature of the NB properties of MGlcDAG.
Highlights
The lipid bilayer of biological membranes acts as a permeability barrier permitting maintenance of essential ion gradients and is the local environment for integral and peripheral membrane proteins
An Escherichia coli mutant lacking the major membrane lipid phosphatidylethanolamine (NBprone) requires divalent cations for viability and cell integrity and is impaired in several membrane functions that are corrected by introduction of the “foreign” NBprone neutral glycolipid ␣-monoglucosyldiacylglycerol (MGlcDAG) synthesized by the MGlcDAG synthase from Acholeplasma laidlawii
To determine whether the affected functions in the E. coli lipid mutant are dependent on the chemical structure of PE or on its NB character we have expressed the gene for the ␣-monoglucosyldiacylglycerol (MGlcDAG) synthase from the mycoplasma Acholeplasma laidlawii [24] in E. coli cells lacking PE
Summary
The lipid bilayer of biological membranes acts as a permeability barrier permitting maintenance of essential ion gradients and is the local environment for integral and peripheral membrane proteins. An alteration in the mutant cell envelope structure or physical properties results in a direct activation of the Cpx stress response pathway [21] Another striking feature of the mutant is a misfolding of the integral membrane transport proteins lactose permease (LacY) and phenylalanine permease; the first six or first two transmembrane helices are inserted in an inverted orientation in the membrane in the former [22] or latter protein [23], respectively. MGlcDAG is an uncharged and major NB-prone lipid that is crucial for bilayer packing properties in the A. laidlawii [25] membrane, varying in amounts from 5 to 50 mol % depending on growth conditions [26] This new E. coli lipid mutant contains up to 55% of the “foreign lipid” MGlcDAG. The MGlcDAG strain compensates for osmotic stress better, and membrane permeability properties are changed but not restored
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
