Rietveld A G, Chupin V V, Koorengevel M C, Wienk H L, Dowhan W, de Kruijff B
Department of Biochemistry of Membranes, Utrecht University, The Netherlands.
J Biol Chem. 1994 Nov 18;269(46):28670-5.
Escherichia coli strain AD93 is unable to synthesize the nonbilayer lipid phosphatidylethanolamine and requires high concentrations of specific divalent cations for growth. Previous studies suggested that in this strain, cardiolipin in combination with divalent cations functionally replaces phosphatidylethanolamine, reflecting polymorphic regulation of membrane lipid composition. However, it is also possible that divalent cations are required for regulation of lipid packing or membrane surface potential. 2H NMR was employed to measure the effect of different divalent cations on lipid packing in aqueous dispersions of lipid extracts isolated from AD93 and the wild type parental strain W3899, which were grown with [11,11-2H2]oleic acid. The results indicate that a range of acyl chain order is compatible with growth and that Ba2+, which cannot support growth of AD93, can increase chain packing to the wild type level. By means of microelectrophoresis, it was shown that the growth-promoting cations and Ba2+ have a strong and comparable ability to screen the surface charge of large unilamellar vesicles prepared from AD93 lipid extracts. Therefore, it is unlikely that the growth-promoting capacity of divalent cations is primarily due to their effect on lipid packing or their potency to decrease the surface potential. Furthermore, the addition of small amounts of Ba2+ to a AD93 lipid dispersion with excess Mg2+ diminished HII phase formation. This observation can explain the growth arrest in AD93 cultures upon the addition of Ba2+ and further supports the conclusion that the cation requirement of this strain arises mainly from polymorphic regulation of lipid composition.
大肠杆菌菌株AD93无法合成非双层脂质磷脂酰乙醇胺，并且需要高浓度的特定二价阳离子才能生长。先前的研究表明，在该菌株中，心磷脂与二价阳离子结合在功能上替代了磷脂酰乙醇胺，这反映了膜脂质组成的多态性调节。然而，二价阳离子也可能是调节脂质堆积或膜表面电位所必需的。采用2H NMR来测量不同二价阳离子对从AD93和野生型亲本菌株W3899中分离的脂质提取物的水性分散体中脂质堆积的影响，这两种菌株均用[11,11-2H2]油酸培养。结果表明，一系列酰基链顺序与生长相容，并且不能支持AD93生长的Ba2+可以将链堆积增加到野生型水平。通过微电泳表明，促进生长的阳离子和Ba2+具有很强且相当的能力来屏蔽由AD93脂质提取物制备的大单层囊泡的表面电荷。因此，二价阳离子的促生长能力不太可能主要归因于它们对脂质堆积的影响或它们降低表面电位的能力。此外，向含有过量Mg2+的AD93脂质分散体中添加少量Ba2+会减少HII相的形成。这一观察结果可以解释添加Ba2+后AD93培养物中的生长停滞，并进一步支持该菌株对阳离子的需求主要源于脂质组成的多态性调节这一结论。
