Bacterial and mammal membranes have different glycerolipid composition. In mammals, phosphatidylcholine glycerolipids predomine but glycerolipid composition also accounts for phosphatidylethanolamine, phosphatidylserine and other phospholipids, it depending on the cell type and, as Marquardt says, on the leaftet.

Variability in glycerolipid composition is also higher in bacterial membranes.

Perhaps the recommendation of Marquardt is the best to begin.

Good luck.

My previous and old experience seuggested that the phospholipids mixture to use for bacterial liposomes should be as fresh as possible; i.e, fresh phospholipids should be purified from hen's egg yolk by yourself at 4 - 8 C.   Phospholipids seemed to be very labile to oxidation or peroxidation, and commercial phospholipids seemed insufficient to use.

See the attached Table!

I've often found the attached reference useful, as well as the website at the following URL: http://opm.phar.umich.edu/atlas.php

One of the nice things about bacterial lipids is that they, with few exceptions, do not contain polyunsaturated fatty acids. Thus, they are less prone to oxidation than mammalian lipids. However, unlike mammalian lipids, which do not vary greatly from species to species (an exception is noted below*), bacterial lipids vary greatly among different phylogenetic groups. If you are trying to mimic E. coli and related genera, it is safe to use a mixture of phosphatidylethanolamine (PE), phosphatidylglycerol and cardiolipin. (See Ratledge and Wilkinson, Microbial Lipids vol. 1; Goldfine, H. Current Topics in Membranes and Transport, vol. 17). Many gram positive species do not have PE. Glycosyldiacylglycerols are commonly found.

*  An exception about mammalian lipids is that the ratio of phosphatidylcholine to sphingomyelin can vary.

Italian National Research Council

Institute of Chemistry of Molecular Recognition ICRM

Rome, Latium, Italia

Dear Dr. Alberto Vitali;

I don’t understand why you are studying on the membrane effect of peptides.

I have studied on the high molecular-weight hydrophobic membrane glycoprotein enzymes, and the membrane effect may be larger in the glycoprotein-membrane enzymes.

Hayakawa K, Oizumi J. Effects of surfactants on human serum biotinidase. Clin Chim Acta 168: 109-111, 1987.

Oizumi J, Hayakawa K. Effect of phospholipids on purified lipoamidase. Experientia 46: 459-461, 1990. (file added)

Effects of gangliosides on human serum biotinidase had been also studied with Dr. Claudio De Felice, Siena University, but this research result has been sadly rejected.

However, biotinidase and lipoamidase activity is under the control of glyco-chains, and hydrophobic molecules (phospholipids and glycolipids); i.e., sequence of core protein is not essential for the enzyme activity..

Hayakawa K, Guo L, Terentyeva EA, Li XK, Kimura H, Hirano M, Yoshikawa K, Nagamine T, Katsumata N, Ogata T, Tanaka T. Determination of specific activities and kinetic constants of biotinidase and lipoamidase in LEW rat and Lactobacillus casei (Shirota). J Chromatogr B 844; 240-250, 2006.

Thus, I would be pleased to hear from you of your achievement.

The most important thing for bacterial plasma membranes - the presence of transmembrane potential. Thus, the experiemnts with model lipid membranes, exploiting liposomes, whose lipid composition is mimicking one of the plasma bacterial membranes, are often useless. Because, the liposome lipid bilayer lacks transmembrane potential. For mammalian membranes the transmembrane potential is not so high, as for bacterial ones. In many cases the liposome experiments are suitable for modeling. In many cases, a single species liposomes, composed of zwitterionic phoshatidylcholine (usually POPC) are good enough. This approach is very often used in MD simulations. However, sometimes, plasma membrane of erythrocytes is modeled with pure PE (phosphatidyethanolamine) lipid.

If, for some reason, you decide to model lipid compisition of bacterial plasma membranes, do not forget that Gram-positive and Gram-negative bacteria have different lipid composition. The latter are usually rich with PE (a good model for many cases is: PE/PG/PC, 7:3:1). The former contain a high proportion of PG (a god model could be PG/PC, 1:1).

Good luck.

I don’t like the idea of transmembrane potential together with fluid mosaic model,

since our group has recently found that such a large molecular weight polysaccharide fucoidan (Mr 200,000) is actively transported.   This finding suggests that the other idea of membrane structure may be required; i.e., the presence of hydrophobic membrane glycoprotein associated with phospholipid and/or glycolipid might be the most important issue.   However, I would like to be informed about the result of your work on hydrophobic peptides associated with phospholipids soon.    

Could someone tell me how to prepare liposomes that mimics gram negative bacterial membrane

I tried POPE:POPG (75:25 mol%) LUV as E. coli model. They became pretty unstable and degraded in a few hours. I used 150 mM NaCl,1 mM EDTA, 5 mM Hepes-NaOH, pH 7.4 buffer. I think there should be a relatively simple way to keep them stable as pH/salt/helator changes etc. I would be happy if someone could find the way to do it.

Any suggestions regarding good/suitable liposomal composition to check bac' membrane pore formation. Thanks.