Chapter 1 Sensory Transduction in Bacteria

Molecular Genetics of Membrane Phospholipid Synthesis

“…As noted above, many types of transmembrane signalling in higher eukaryotes have been attributed to sn-I ,2-diglyceride formation derived from the turnover of minor, phosphorylated metabolites of phosphatidylinositol (14, 65, 157). A prokaryotic counterpart to the "phosphatidylinositol cycle" has not been reported, but in this context, a role for some of the minor lipids of E. coli as modulators of chemotaxis (140,218) deserves consideration. Certain minor lipids might also function as regulators of the enzymes involved in the synthesis of the major components (Figures 3-5) or in other membrane associated processes.…”

Methyl-accepting protein associated with bacterial sensory rhodopsin I

“…Biol.). This behavior, as well as that of Pho72 and its revertants, is analogous to the behavior of E. coli, in which methylation promotes swimming reorientation (tumbling) so that cells are adapted to attractants (6,9,11,20,21). Undermethylation, such as that which occurs after methionine starvation or in a protein methyltransferase mutant, leads to smooth swimming in E. coli.…”

“…This adaptation is essential for the cells to sense gradients, i.e., to respond to changes rather than to absolute levels of light intensity and chemical effectors (11). In chemotactic eubacteria (e.g., Escherichia coli), one mechanism of adaptation is by rarboxylmethylation of transmembrane chemoreceptors (6,9,11,20,21).…”

Sensory rhodopsins I and II modulate a methylation/demethylation system in Halobacterium halobium phototaxis.

“…The 94-kDa protein resembles the chemotaxis signal generators ("transducers") of eubacteria (e.g., Escherichia colt), which transmit chemoreceptor signals from the membrane to a cytoplasmic sensory pathway. In eubacteria methylation of the transducers occurs by carboxylmethyl esterification of glutamate residues in the signal-transmitting domain and mediates adaptation to chemostimuli (17)(18)(19)(20).…”

“…The 94-kDa protein resembles the chemotaxis signal generators ("transducers") of eubacteria (e.g., Escherichia colt), which transmit chemoreceptor signals from the membrane to a cytoplasmic sensory pathway. In eubacteria methylation of the transducers occurs by carboxylmethyl esterification of glutamate residues in the signal-transmitting domain and mediates adaptation to chemostimuli (17)(18)(19)(20).Reversible protein methylation was implicated in phototaxis and chemotaxis adaptation in H. halobium before the identification of specific taxis receptors (21-25). Methylaccepting membrane proteins in the 90-to 150-kDa range can be visualized by autofluorography of protein gels and are lost in taxis-mutants (16,26), are regained upon reversion to taxis' (16), and exhibit changes in extent of methylation induced by chemostimuli (26).…”