ECTD

EctD is the gene encoding the ectoine hydroxylase, an enzyme that converts the compatible solute ectoine into 5-hydroxyectoine in a range of bacteria. It is a member of the non-heme iron(II)-dependent 2-oxoglutarate (2OG) dioxygenase family. In the catalytic cycle, EctD uses Fe2+ and 2-oxoglutarate as cofactors to activate molecular oxygen, hydroxylating the ectoine substrate to yield 5-hydroxyectoine, with succinate and CO2 produced from 2OG.

Genetic context and occurrence: EctD is typically encoded within or adjacent to the ectoine biosynthesis gene cluster (ectABC) and is common in osmoresponsive bacteria, particularly halophiles and marine isolates. EctD activity contributes to the intracellular pool of hydroxyectoine, a more effective compatible solute under high-salt stress.

Structure and mechanism: EctD proteins share the characteristic 2OG-Fe(II) dioxygenase fold and a conserved metal-binding motif, commonly described as HxD...H, coordinating Fe2+. The substrate-binding region is adapted for ectoine recognition, and many orthologs are predicted to function as homodimers or higher-order oligomers.

Applications and significance: Hydroxyectoine produced by EctD-containing pathways has commercial value as a protectant against temperature and desiccation in cosmetics and enzyme formulations. Understanding EctD facilitates metabolic engineering of microbes to enhance hydroxyectoine production for industrial use.