Dimerization is required for the activity of the protein histidine kinase CheA that mediates signal transduction in bacterial chemotaxis.
The histidine protein kinase CheA plays an essential role in stimulus-response coupling during bacterial chemotaxis. The kinase is a homodimer that catalyzes the reversible transfer of a gamma-phosphoryl group from ATP to the N-3 position of one of its own histidine residues. Kinetic studies of rates of autophosphorylation show a second order dependence on CheA concentrations at submicromolar levels that is consistent with dissociation of the homodimer into inactive monomers. The dissociation was confirmed by chemical cross-linking studies. The dissociation constant (CheA2<==>2CheA; KD = 0.2-0.4 microM) was not affected by nucleotide binding, histidine phosphorylation, or binding of the response regulator, CheY. The turnover number per active site within a dimer (assuming 2 independent sites/dimer) at saturating ATP was approximately 10/min. The kinetics of autophosphorylation and ATP/ADP exchange indicated that the dissociation constants of ATP and ADP bound to CheA were similar (KD values approximately 0.2-0.3 mM), whereas ATP had a reduced affinity for CheA approximately P (KD approximately 0.8 mM) compared with ADP (KD approximately 0.3 mM). The rates of phosphotransfer from bound ATP to the phosphoaccepting histidine and from the phosphohistidine back to ADP seem to be essentially equal (kcat approximately 10 min-1).
Surette
M G
MG
Department of Molecular Biology, Princeton University, New Jersey 08544, USA.
Levit
M
M
Liu
Y
Y
Lukat
G
G
Ninfa
E G
EG
Ninfa
A
A
Stock
J B
JB
D001426:Bacterial Proteins; D002633:Chemotaxis; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D000071677:Histidine Kinase; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D000072236:Methyl-Accepting Chemotaxis Proteins; D011487:Protein Conformation; D011494:Protein Kinases / Q000378:metabolism; D012486:Salmonella typhimurium; D015398:Signal Transduction
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; C000607606:cheY protein, E coli; D011494:Protein Kinases; D000071677:Histidine Kinase; C000607608:cheA protein, E coli