Ketohexokinase (KHK) catalyzes the ATP-dependent phosphorylation of fructose, forming fructose-1-phosphate and ADP. The enzyme is well studied in Eukarya, in particular in human and other vertebrates, but homologs have not been identified in Bacteria and Archaea. Here we report the identification of a novel type of KHK from the haloarchaeon Haloferax volcanii (HvKHK). The encoding gene khk was identified as HVO_1812. The gene was expressed as 90 kDa homodimeric protein, catalyzing the phosphorylation of fructose with a Vmax value of 59 U/mg and apparent KM values for ATP and fructose of 0.47 mM and 1.29 mM, respectively. Homologs of HvKHK were only identified in few haloarchaea and halophilic Bacteria. The protein showed low sequence identity to characterized KHKs from eukaryotes and phylogenetic analyses indicate that haloarchaeal KHKs are largely separated from eukaryal KHKs. This is the first report of the identification of KHKs in prokaryotes that form a novel cluster of sugar kinases within the ribokinase/pfkB superfamily.

中文翻译：

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盐古菌 Haloferax volcanii 中新型酮己糖激酶的鉴定和表征

酮己糖激酶 (KHK) 催化果糖的 ATP 依赖性磷酸化，形成果糖-1-磷酸和 ADP。这种酶在真核生物中得到了充分研究，特别是在人类和其他脊椎动物中，但尚未在细菌和古细菌中鉴定出同源物。在这里，我们报告了从盐古菌 Haloferax volcanii (HvKHK) 中鉴定出一种新型 KHK。编码基因khk被鉴定为HVO_1812。该基因表达为 90 kDa 同二聚体蛋白，催化果糖磷酸化，Vmax 值为 59 U/mg，ATP 和果糖的表观 KM 值分别为 0.47 mM 和 1.29 mM。 HvKHK 的同系物仅在少数盐古菌和嗜盐细菌中被发现。该蛋白质与来自真核生物的特征性 KHK 表现出较低的序列同一性，系统发育分析表明盐古菌 KHK 在很大程度上与真核 KHK 分离。这是在原核生物中鉴定出 KHK 的第一份报告，这些 KHK 在核激酶/pfkB 超家族中形成了一个新的糖激酶簇。