Arrangement of phosphatidylethanolamine molecular species in Escherichia coli membranes and reconstituted lipids as determined by dimethyl suberimidate cross-linking of nearest neighbor lipids

Topology and transport of membrane lipids in bacteria

The last two decades have witnessed a break-through in identifying and understanding the functions of both the proteins and lipids of bacterial membranes. This development was parallelled by increasing insights into the biogenesis, topology, transport and sorting of membrane proteins. However, progress in research on the membrane distribution and transport of lipids in bacteria has been slow in that period. The development of novel biochemical in vitro approaches and recent genetic studies have increased our understanding of these subjects. The aim of this review is to present an overview of the current knowledge of the distribution and transport of lipids in both Gram-positive and Gram-negative bacteria. Special attention is paid to recently obtained results, which are expected to inspire further research to finally unravel these poorly understood phenomena.

Structural characterization of molecular phospholipid species in cytoplasmic membranes of the cell wall-less Streptomyces hygroscopicus L form by use of electrospray ionization coupled with collision-induced dissociation mass spectrometry

A comparative analysis of the lipid compositions and fatty acids in the cytoplasmic membranes of Streptomyces hygroscopicus and its stable cell wall-less L form has been carried out to detect the differences which may be involved in the altered properties of the L-form membranes. Because only quantitative differences could be found (8), we analyzed the lipid components at the molecular level. Electrospray ionization (ESI), collision-induced dissociation (CID), and tandem mass spectrometry (MS-MS) were used for qualitative detection and quantitative determination of the molecular lipid species in phosphatidylethanolamine (PE1), lyso-cardiolipin (LCL), and cardiolipin (CL). Each phospholipid, isolated by preparative high-performance liquid chromatography showed several homologous molecular ion groups (PE1, four groups; LCL, six groups; CL, six groups) in the negative ESI-MS spectra. The sizes of the peaks represent their relative amounts in the corresponding phospholipid classes. Structural details about individual components of the molecular ion groups were obtained by mass selection and CID with MS-MS. Product ions derived from CID (daughter ions) give information about the molecular weights of the acyl constituents. The qualitative and quantitative compositions of the molecular species were determined by combining the data from the fatty acid pattern obtained by gas chromatography (GC), the relative quantities of the molecular ion groups, and the acyl constituents detected in these molecular ions. Because the ESI-MS-CID-MS data do not allow us to distinguish between n, iso, and anteiso fatty acids of the same molecular weight, it has been assumed that the ratio of these equal-numbered fatty acids determined by GC analysis of the isolated fatty acids is also present in the CID-MS peaks. In this way, 18 species were found in PE1, 43 species were estimated in LCL, and 59 species were ascertained for CL.

Lipid domains in model and biological membranes

Lipid domains that occur within biological of model membranes encompass a variety of structures with very different lifetimes. The separation of membrane lipids into compositional domains can be due to lateral phase separation, immiscibility within a single phase, or interaction of lipids with integral or peripheral proteins. Lipid domains can affect the extent and rate of reactions in the membrane and provide sites for the activity of specialized proteins. Domains are likely to be involved in the process of lipid sorting to various cellular membranes, as well as in other processes which involve membrane budding or invagination.