The hybrid histidine kinase Slr1759 of the cyanobacterium Synechocystis sp. PCC 6803 contains FAD at its PAS domain

Abstract

The cyanobacterium Synechocystis sp. PCC 6803 harbours 47 histidine kinases (Hiks). Among these are hybrid histidine kinases with one or two response regulator domains as well as numerous Hiks with several sensory domains. One example is the hybrid histidine kinase Slr1759 (Hik14) that has two PAS domains arranged in tandem linked to a predicted GAF domain. Here, we show that a Slr1759 derivative recombinantly expressed in Escherichia coli has a Xavin cofactor. Using truncated Slr1759 variants, it is shown that the Xavin associates with the Wrst PAS domain. The cofactor reconstitutes the activity of Damino acid oxidase apoprotein from pig kidney, indicating that the Xavin derivative is FAD. Furthermore, the Slr1759 histidine kinase domain indeed undergoes autophosphorylation in vitro. The phosphorylated product of a recombinant Slr1759 derivative is sensitive to acids, pointing to a histidine residue as the phosphate-accepting group.