Identification and characterization of 2-keto-3-deoxygluconate kinase and 2-keto-3-deoxygalactonate kinase in the haloarchaeon Haloferax volcanii

Abstract

The halophilic archaeon Haloferax volcanii has been proposed to degrade glucose via the semi-phosphorylative Entner-Doudoroff pathway, involving 2-keto-3-deoxygluconate kinase (KDGK) as key enzyme. So far, neither the enzyme has been characterized nor the encoding gene has been identified. In the genome of H. volcanii, two genes, HVO_0549 (kdgK1) and HVO_A0328 (kdgK2), are annotated encoding putative KDGK-1 and KDGK-2. To identify the physiological role of both kinases, transcriptional regulation analyses of both genes and growth experiments of the respective deletion mutants were performed on different sugars. Further, recombinant KDGK-1 and KDGK-2 were characterized. Together, the data indicate that KDGK-1 represents the functional constitutively expressed KDG kinase in glucose degradation, whereas KDGK-2 is an inducible 2-keto-3-deoxygalactonate kinase likely involved in d-galactose catabolism. The paper describes the identification of KDGK-1 as functional 2-keto-3-deoxygluconate kinase in the semi-phosphorylative ED pathway of glucose degradation and of KDGK-2 as 2-keto-3-deoxygalactonate kinase in galactose degradation in H. volcanii. Both enzymes belong to the PFK (phosphofructokinase)-B family of carbohydrate kinases.