Histidine kinases (HK) are multifunctional, and in non-animal kingdoms, typically transmembrane, proteins of the transferase class of enzymes that play a role in signal transduction across the cellular membrane.

HKs are known to serve roles in many different signal transduction pathways, so it is not surprising that the extracellular sensing domain is not very well conserved in the HK family.

This residue is invariant and forms a hydrogen bond along with a water molecule to the adenine amine group.

When the γ phosphate of ATP is destabilized, the Mg2+ is no longer observed due to its inability to octahedrally coordinate.

Marina et al. argue that similar coordination of Mg2+ occurs in HK853 but that it is unobserved due to the usage of the ATP analog AMPPNP in the crystal structure.

Also the presence of the nucleotide base has proved to play a significant role in stabilization of the lid in a closed conformation.

The Nε of His-260 then attacks the γ phosphate of ATP in a nucleophilic addition and bumps off ADP as its leaving group.

[10] C. albicans with a deletion of CHK1, the two-component histidine kinase gene, show defects in morphogenesis and a drastic decrease in the cell’s ability to resist elimination by human neutrophils.

As humans lack this two-component system, it may be a good target for anti-microbial agents in order to treat candidiasis.