Different Evolutionary Constraints on Chemotaxis Proteins CheW and CheY Revealed by Heterologous Expression Studies and Protein Sequence Analysis

Abstract

CheW and CheY are single-domain proteins from a signal transduction pathway that transmits information from transmembrane receptors to flagellar motors in bacterial chemotaxis. In various bacterial and archaeal species, the cheW and cheY genes are usually encoded within homologous chemotaxis operons. We examined evolutionary changes in these two proteins from distantly related proteobacterial species, Escherichia coli and Azospirillum brasilense. We analyzed the functions of divergent CheW and CheY proteins from A. brasilense by heterologous expression in E. coli wild-type and mutant strains. Both proteins were able to specifically inhibit chemotaxis of a wild-type E. coli strain; however, only CheW from A. brasilense was able to restore signal transduction in a corresponding mutant of E. coli. Detailed protein sequence analysis of CheW and CheY homologs from the two species revealed substantial differences in the types of amino acid substitutions in the two proteins. Multiple, but conservative, substitutions were found in CheW homologs. No severe mismatches were found between the CheW homologs in positions that are known to be structurally or functionally important. Substitutions in CheY homologs were found to be less conservative and occurred in positions that are critical for interactions with other components of the signal transduction pathway. Our findings suggest that proteins from the same cellular pathway encoded by genes from the same operon have different evolutionary constraints on their structures that reflect differences in their functions.

A chemoreceptor from Pseudomonas putida forms active signalling complexes in Escherichia coli

“…Thus, there is no strict length-class specificity between receptors and the CheA kinase under their control. Likewise, the CheW coupling protein has been shown to be exchangeable between distantly related bacterial species (Alexandre & Zhulin, 2003;Hamblin et al, 1997).…”

Virulence Factors Encoded by Legionella longbeachae Identified on the Basis of the Genome Sequence Analysis of Clinical Isolate D-4968

“…6). A gene encoding the response regulator CheY is usually included in a chemotaxis operon (2,90), but a cheY homolog was not found in the operon of D-4968. Two genes, LLB_2022 and LLB_2292 located outside the chemotaxis operon, encode CheY-like proteins, which may function together with the gene products of the chemotaxis operon.…”

An Energy Taxis Transducer Promotes Root Colonization byAzospirillum brasilense

“…Mutations in the A. brasilense chemotaxis operon abolish taxis to all known stimuli and affect the pattern of motility (20), suggesting that this operon is the major regulator of motile behavior. It has also been shown that, despite their divergence in sequence, the chemotaxis proteins of A. brasilense are functional homologs of their E. coli counterparts (5).…”