Regulation of Bacterial Membrane Lipid Synthesis

This chapter discusses the mechanisms regulating the synthesis of bacterial membrane lipid. The regulation of synthesis of membrane lipid can be achieved by (1) control of membrane phospholipid acyl-group composition and (2) regulation of the rate of phospholipid synthesis. Major progress on the sn-glycerol-3-phosphate acyltransferase is permitted by genetic cloning and by synthesis of native acyl-ACP substrates. A similar combination of genetic and biochemical approaches has led to a detailed knowledge of the mechanism of temperature control. β-ketoacyl-ACP synthase II is required for temperature control. This enzyme is not involved in isothermal control. β-ketoacyl-ACP synthase II therefore seems tailored for its role in temperature regulation, and temperature control seems to be superimposed on the normal (isothermal) regulatory mechanism. E. coli developed temperature control by evolving a temperature-sensitive isozyme to catalyze the synthesis of the required unsaturated fatty acid. Although simple regulatory mechanisms such as that of temperature control explains the phenomenology of the regulation of bacterial lipid synthesis, the regulation of phospholipid synthesis by the relA gene may be an exception. The unreliable nature of results obtained in vitro means that sophisticated approaches must be developed to ascertain the physiological relevance of ppGpp inhibition of a given enzyme.