Protein kinase CheY/CheA complex (bacteria chemotaxis)
Escherichia coli (bacteria)
One of the signaling mechanisms employed by nature is the phosphorylation of certain protein amino acid sidechains. The proteins which carry out the phosphorylation are called protein kinases. They are divided into three different classes, depending on which type of sidechain they phosphorylate: tyrosine kinases, serine/threonine kinases and histidine kinases. The protein kinases are larger proteins with several functional domains.
Here we see one of these functional domains of a particular histidine kinase, CheA, as a complex with a related protein CheY. CheY is the protein that becomes phosphorylated by the kinase domain of CheA and the fragment here is the part of the protein that bind to CheY to orient it for this step. CheA is used by bacteria to respond to chemical changes in their environment. It becomes autophosphorylated in response to certain chemical signals and then donates the phosphate to CheY. This process controls the motion of the bacterial flagella which propel it forward. Together they switch the direction of rotation of these flagella. When the flagella rotate counterclockwise, the bacterium moves smoothly in one direction. Switching the rotation to clockwise rotation results in a direction change. CheY is the switch that accomplishes this under the control of CheA. Both CheY and the CheY-binding domain are rather compact. The larger molecule is CheY and the smaller one the CheA fragment. As one can see, the surface of CheY has a dent, into which the convex surface of the CheA fragment fits.
Protein Data Bank (PDB)
author: Arno Paehler