Comparisons between the three‐dimensional structures of the chemotactic protein Che Y and the normal Gly 12‐p21 protein

The three‐dimensional structure of a chemotactic protein Che Y from Salmonella typhimurium has recently been determined by X‐ray crystallography. The structure of this small protein, containing 129 amino acid residues, shows a domain consisting of a central beta‐pleated sheet surrounded on both sides by alpha‐helices. We have examined the sequence and the arrangement of the structural domains of the Che Y protein and have compared them with other nucleotide binding protein sequences and structures. We find that the Che Y protein has significant sequence homology to the ras‐gene encoded p21 protein. In addition, the structural domains of the two proteins are arranged in a fundamentally similar manner, including the phosphate‐binding site (both proteins bind phosphate‐containing ligands). The striking similarity in the arrangement of the structural domains of the two proteins suggests that both may serve similar functions as signal transducers.