Phosphatidylethanolamine and phosphatidylglycerol are segregated into different domains in bacterial membrane. A study with pyrene‐labelled phospholipids

Abstract

SummaryTo detect and characterize membrane domains that have been proposed to exist in bacteria, two kinds of pyrene-labelled phospholipids, 2-pyrene-decanoylphosphatidylethanolamine (PY-PE) and 2-pyrenedecanoyl-phosphatidylglycerol (PY-PG) were inserted into Escherichia coli or Bacillus subtilis membrane. The excimerization rate coefficient, calculated from the excimer-to-monomer ratio dependencies on the probe concentration, was two times higher for PY-PE than for PY-PG at 37 ∞ ∞ ∞ ∞ C. This was ascribed to different local concentrations rather than to differences in mobility. The extent of mixing between the two fluorescent phospholipids, estimated by formation of their heteroexcimer, was found very low both in E. coli and B. subtilis , in contrast to model membranes. In addition, these two pyrene derivatives exhibited different temperature phase transitions and different detergent extractability, indicating that the surroundings of these phospholipids in bacterial membrane differ in organization and order. Inhibition of protein synthesis, leading to condensation of nucleoid and presumably to dissipation of membrane domains, indeed resulted in increased formation of heteroexcimers, broadening of phase transitions and equal detergent extractability of both probes. It is proposed that in bacterial membranes these phospholipids are segregated into distinct domains that differ in composition, proteo-lipid interaction and degree of order; the proteo-lipid domain being enriched by PE.

Lipids in the inner membrane of dormant spores of Bacillus species are largely immobile

“…There is at least one report that the spore's inner membrane has a significantly higher protein content than the growing cell membrane (48), and a high level of protein in the spore's inner membrane might serve to organize large areas of ordered domains under the special conditions of dehydration of the spore core. Evidence consistent with the existence of distinct domains in the membrane of growing cells of B. subtilis has been presented (49). It was also reported that the inner membrane of B. megaterium spores could be resolved into approximately equivalent amounts of two fractions of similar lipid composition, but markedly different protein content and composition (50).…”

Lipids Trigger a Conformational Switch That Regulates Signal Recognition Particle (SRP)-mediated Protein Targeting

“…This supports the idea that the MTS of FtsY is tuned to the anionic phospholipid content of the E. coli membrane. Lipid segregation in bacterial membranes is well documented (37) and might restrict binding of FtsY to specific sites at the inner membrane. Indeed, anionic phospholipids have been found to be enriched at the SecYEG translocation channel (38).…”

Dynamic localization of membrane proteins in Bacillus subtilis

“…In particular, the use of specific fluorescent probes has indicated that the phospholipid cardiolipin localizes preferentially to the cell poles and division sites (mid-cell regions) of both Gram-positive and Gram-negative bacteria (Mileykovskaya & Dowhan, 2000;Kawai et al, 2004). Further experiments using 2-pyrene derivatives of the phospholipids phosphatidylethanolamine (PE) and phosphatidyleglycerol (PG) indicated that the two lipids segregate into distinct domains in both Grampositive and Gram-negative cell membranes, and that the PE domains were enriched for protein content (Vanounou et al, 2003). Despite the similarity of results obtained with Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) model systems, the two organisms have quite different proportions of common phospholipids in their cytoplasmic membranes.…”