Influence of attractants and repellents on methyl group turnover on methyl-accepting chemotaxis proteins of Bacillus subtilis and role of CheW

Abstract

The ability of attractants and repellents to affect the turnover of methyl groups on the methyl-accepting chemotaxis proteins (MCPs) was examined for Bacillus subtilis. Attractants were found to cause an increase in the turnover of methyl groups esterified to the MCPs, while repellents caused a decrease. These reactions do not require CheW. However, a cheW null mutant exhibits enhanced turnover in unstimulated cells. Assuming that the turnover of methyl groups on the MCPs reflects a change in the activity of CheA, these results suggest that the activation of CheA via chemoeffector binding at the receptor does not require CheW.Escherichia coli has been the prototype for understanding chemotactic sensory transduction in bacteria. In E. coli, when a chemoeffector binds to the receptors, or methylaccepting chemotaxis proteins (MCPs), a conformational change occurs in the receptor, which transmits the information from the periplasmic space to the cytoplasm (30). The addition of attractant in the presence of CheW is believed to inhibit the autophosphorylation of CheA such that the level of CheY-P subsequently decreases (7,21). CheY-P is thought to bind to the switch to cause clockwise rotation of the flagella (20,23,27,28,36,37). The addition of attractant also increases the rate of methylation of the MCPs by the methyltransferase (13) CheR such that the rate of CheA autophosphorylation can return to normal (29), thus allowing the bacteria to adapt. Repellents are believed to increase the rate of autophosphorylation of CheA and hence the level of CheY-P (6), inducing the bacteria to tumble. However, CheA-P also phosphorylates CheB, and CheB-P, which is the activated form of the methylesterase (17), rapidly demethylates the MCPs so that CheA-P returns to the prestimulus level (20).Chemotaxis in Bacillus subtilis has significant similarities to as well as differences from chemotaxis in E. coli. For instance, B. subtilis has homologs to CheA (10), CheB (11,19), CheR (8, 9), CheW (14), and CheY (3). CheA in B. subtilis, like that in E. coli, is probably the master controller of chemotaxis, because excitation does not occur in a cheA null mutant (10). However, a novel reaction, whereby attractants cause a high rate of turnover of methyl groups on the MCPs, occurs in B. subtilis. These methyl groups remain in the system, rather than evolving directly as methanol, since they return to the MCPs (32-34) when the attractant is removed. It is believed that these methyl groups are transferred to a regulator protein, but its function is not presently understood (2, 31-34). Another significant comparison between E. coli and B. subtilis is the switch that controls the direction of flagellar rotation. Both organisms have FliM (38) and FliG (1) homologs. In addition, E. coli has a small (14-kDa) protein, FliN (15,18)

Large increases in attractant concentration disrupt the polar localization of bacterial chemoreceptors

“…Some bacteria, including B. subtilis , express CheV, a CheW homologue with an additional response regulator (CheY‐like) domain (Fredrick and Helmann, 1994; Rosario et al ., 1994; Pittman et al ., 2001). In E. coli , methanol release (demethylation) occurs only in response to repellents (negative stimuli) (Stock and Koshland, 1978), whereas methanol is released from B. subtilis in response to all stimuli (Goldman et al ., 1982; Hanlon et al ., 1992b; Zimmer et al ., 2000). In E. coli , attractant binding leads to a decrease in CheA phosphorylation, a decrease in CheY phosphorylation, and a subsequent running response.…”

The role of heterologous receptors in McpB‐mediated signalling in Bacillus subtilis chemotaxis

“…Adding asparagine to McpB‐containing membranes in vitro activates an associated autophosphorylating histidine kinase, CheA (Garrity and Ordal, 1997). CheA is associated with the receptor by either of two proteins, CheW and CheV (Hanlon et al. , 1992a,b; Frederick and Helmann, 1994; Rosario et al.…”

Amino acid efflux in response to chemotactic and osmotic signals in Bacillus subtilis

“…Butyrate is a strong repellent of B. subtilis but is also used at high concentrations (11). As a result, the colligative properties of aspartate and butyrate stimuli must be considered.…”