# HD domain

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In molecular biology, the **HD domain** is a conserved [protein domain](/source/Protein_domain), named after the conserved [histidine](/source/Histidine) (H) and/or [aspartate](/source/Aspartic_acid) (D) [amino acid](/source/Amino_acid) residues. It is found in a superfamily of [enzymes](/source/Enzyme) with a predicted or known phosphohydrolase activity. These enzymes appear to be involved in [nucleic acid](/source/Nucleic_acid) metabolism, [signal transduction](/source/Signal_transduction) and possibly other functions in [bacteria](/source/Bacteria), [archaea](/source/Archaea) and [eukaryotes](/source/Eukaryotes). The fact that all the highly conserved residues in the HD superfamily are [histidines](/source/Histidines) or [aspartates](/source/Aspartate) suggests that coordination of [divalent](/source/Divalent) [cations](/source/Cations) is essential for the activity of these [proteins](/source/Protein).[1]

## References

1. Aravind L, Koonin EV (December 1998). "The HD domain defines a new superfamily of metal-dependent phosphohydrolases". *Trends in Biochemical Sciences*. **23** (12): 469–72. [doi:10.1016/s0968-0004(98)01293-6](https://doi.org/10.1016/s0968-0004(98)01293-6). [PMID 9868367](https://pubmed.ncbi.nlm.nih.gov/9868367)

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Adapted from the Wikipedia article [HD domain](https://en.wikipedia.org/wiki/HD_domain) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/HD_domain?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.