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Highly Accessed Protein family review

Histidine protein kinases: key signal transducers outside the animal kingdom

Peter M Wolanin1, Peter A Thomason1 and Jeffry B Stock12*

Author Affiliations

1 Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA

2 Department of Chemistry, Princeton University, Princeton, NJ 08544, USA

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Genome Biology 2002, 3:reviews3013-reviews3013.8  doi:10.1186/gb-2002-3-10-reviews3013

Published: 25 September 2002

Abstract

Histidine protein kinases (HPKs) are a large family of signal-transduction enzymes that autophosphorylate on a conserved histidine residue. HPKs form two-component signaling systems together with their downstream target proteins, the response regulators, which have a conserved aspartate in a so-called 'receiver domain' that is phosphorylated by the HPK. Two-component signal transduction is prevalent in bacteria and is also widely used by eukaryotes outside the animal kingdom. The typical HPK is a transmembrane receptor with an amino-terminal extracellular sensing domain and a carboxy-terminal cytosolic signaling domain; most, if not all, HPKs function as dimers. They show little similarity to protein kinases that phosphorylate serine, threonine or tyrosine residues, but may share a distant evolutionary relationship with these enzymes. In excess of a thousand known genes encode HPKs, which are important for multiple functions in bacteria, including chemotaxis and quorum sensing, and in eukaryotes, including hormone-dependent developmental processes. The proteins divide into at least 11 subfamilies, only one of which is present in eukaryotes, suggesting that lateral gene transfer gave rise to two-component signaling in these organisms.