Bacterial membranes lipid synthesis

Cronan, J.E., Jr. 2003. Bacterial membrane lipids where do we stand Annu. Rev. Microbiol. 57 203-224. Schujman, G.E., de Mendoza, D. 2005. Transcriptional control of membrane lipid synthesis in bacteria. Curr. Opin. Microbiol. 8 149-153. 

Many of the proteins of membranes are enzymes. For example, the entire electron transport system of mitochondria (Chapter 18) is embedded in membranes and a number of highly lipid-soluble enzymes have been isolated. Examples are phosphatidylseiine decarboxylase, which converts phosphatidylserine to phosphatidylethanolamine in biosynthesis of the latter, and isoprenoid alcohol phosphokinase, which participates in bacterial cell wall synthesis (Chapter 20). A number of ectoenzymes are present predominantly on the outsides of cell membranes.329 Enzymes such as phospholipases (Chapter 12), which are present on membrane surfaces, often are relatively inactive when removed from the lipid environment but are active in the presence of phospholipid bilay-ers.330 33 The distribution of lipid chain lengths as well as the cholesterol content of the membrane can affect enzymatic activities.332... 

The outer surfaces of bacteria are rich in specialized polysaccharides. These are often synthesized while attached to lipid membrane anchors as indicated in a general way in Eq. 20-20.136/296a One of the specific biosynthetic cycles (Fig. 20-9) that depends upon undeca-prenol phosphate is the formation of the peptidoglycan (murein) layer (Fig. 8-29) of both gram-negative and gram-positive bacterial cell walls. Synthesis begins with attachment of L-alanine to the OH of the lactyl... 

Undecaprenol (bactoprenol) from Salmonella contains eleven isoprene units, and two irons and nine cis double bonds In the form of undecaprenyl phosphate, it acts as a carrier of carbohydrate residues in the biosynthesis of bacterial antigenic polysaccharides synthesis of Murein (see) also depends on undecaprenyl phosphate. In eukaryotes the Dolichol phosphates (see) function in the transfer of carbohydrate residues in the synthesis of glycoproteins and glycoli-pids. Probably the long lipid chains of these P serve to anchor them in membranes, while the phosphate group acts as a carrier by protruding into the cytoplasm. It is not known whether all P. function as carbohydrate carriers. The structural relationship between solanesol and plastoquinone-9 and ubiquinone-9, and the joint occurrence of these compounds suggest a precursor role for P. Biosynthesis of P. proceeds from mevalonic acid and the conformation of all double bonds is predetermined in early precursors. 

We have been interested in the regulation of the synthesis of membrane proteins and lipids. In particular, we have tried to answer several questions Are bacterial membrane proteins synthesized in the absence of lipid synthesis Are these proteins, if synthesized, integrated into the membrane If the proteins are integrated into the membrane, can they function when introduced in the absence of lipid synthesis These questions have been probed with bacterial mutants auxotrophic for glycerol, an essential constituent of all major classes of phospholipids. 

Bacterial lipoproteins are anchored at the membrane by their covalently linked lipid moiety. Although they are first anchored at the inner membrane on their synthesis, some portion of them are then transfered to the outer membrane. Therefore, some sorting machinery must exist. It has been revealed that there is a specific pathway that includes the... 

M Matsuhashi. Utilization of lipid-linked precursors and the formation of peptidoglycan in the process of cell growth and division membrane enzymes involved in the final steps of peptidoglycan synthesis and the mechanism of their regulation. In JM Ghuysen, R Hakenbeck, eds. Bacterial Cell Wall. Amsterdam, The Netherlands Elsevier Science, 1994, pp 55-72. 

Penicillin interferes with the synthesis of the bacterial cell wall. A nucleophilic OH group of the glycopeptide transpeptidase enzyme cleaves the P-lactam ring of penicillin by a nucleophilic acyl substitution reaction. The opened ring of the penicillin molecule remains covalently bonded to the enzyme, thus deactivating the enzyme, halting cell wall construction, and killing the bacterium. Penicillin has no effect on mammalian cells because they are surrounded by a flexible membrane composed of a lipid bilayer (Chapter 3) and not a cell wall. 

---