Phosphorylation of the response regulator CheV is required for adaptation to attractants during Bacillus subtilis chemotaxis.

In the Gram-positive soil bacterium Bacillus subtilis, the chemoreceptors are coupled to the central two-component kinase CheA via two proteins, CheW and CheV. CheV is a two-domain protein with an N-terminal CheW-like domain and a C-terminal two-component receiver domain. In this study, we show that CheV is phosphorylated in vitro on a conserved aspartate in the presence of phosphorylated CheA (CheA-P). This reaction is slower compared with the phospho-transfer reaction between CheA-P and one other response regulator of the system, CheB. CheV-P is also highly stable in comparison with CheB-P. Both of these properties are more pronounced in the full-length protein compared with a truncated form composed only of the receiver domain, that is, deletion of the CheW-like domain results in increase in the rate of the phospho-transfer reaction and decrease in stability of the phosphorylated protein. Phosphorylation of CheV is required for adaptation to the addition of the chemoattractant asparagine. In tethered-cell assays, strains expressing an unphosphorylatable point mutant of cheV or a truncated mutant lacking the entire receiver domain are severely impaired in adaptation to the addition of asparagine. Both of these strains, however, show near normal counterclockwise biases, suggesting that in the absence of the attractant the chemoreceptors are efficiently coupled to CheA kinase by the mutant CheV proteins. Inability of the CheW-like domain of CheV to support complete adaptation to the addition of asparagine also suggests that unlike CheW, this domain by itself may lead to the formation of signaling complexes that stay overactive in the presence of the attractant. A possible structural basis for this feature is discussed.

Myoglobin-like aerotaxis transducers in Archaea and Bacteria.

Haem-containing proteins such as haemoglobin and myoglobin play an essential role in oxygen transport and storage. Comparison of the amino-acid sequences of globins from Bacteria and Eukarya suggests that they share an early common ancestor, even though the proteins perform different functions in these two kingdoms. Until now, no members of the globin family have been found in the third kingdom, Archaea. Recent studies of biological signalling in the Bacteria and Eukarya have revealed a new class of haem-containing proteins that serve as sensors. Until now, no haem-based sensor has been described in the Archaea. Here we report the first myoglobin-like, haem-containing protein in the Archaea, and the first haem-based aerotactic transducer in the Bacteria (termed HemAT-Hs for the archaeon Halobacterium salinarum, and HemAT-Bs for Bacillus subtilis). These proteins exhibit spectral properties similar to those of myoglobin and trigger aerotactic responses.