The crystal structure of the "Caulobacter crescentus" histidine phosphotransferase protein ChpT in dimeric form. The four helices shown in yellow comprise the conserved four-helix bundle, with the histidine phosphorylation sites highlighted in green. The domains shown in red and tan are pseudo-CA domains that resemble the ATP-binding domains of histidine kinases, but do not bind or hydrolyze ATP. Compare this structure to 1c02.png, depicting a monomeric Hpt. Rendered using PyMol from PDB ID 4FMT.