Characterization of a Novel Glucosamine-6-Phosphate Deaminase from a Hyperthermophilic Archaeon

Akey step in amino sugar metabolism is the interconversion betweenfructose-6-phosphate (Fru6P) and glucosamine-6-phosphate (GlcN6P). Thisconversion is catalyzed in the catabolic and anabolic directions byGlcN6P deaminase and GlcN6P synthase, respectively, two enzymes thatshow no relationship with one another in terms of primary structure. Inthis study, we examined the catalytic properties and regulatoryfeatures of theglmD gene product (GlmDTk )present within a chitin degradation gene cluster in thehyperthermophilic archaeonThermococcus kodakaraensis KOD1.Although the protein GlmDTk was predicted as aprobable sugar isomerase related to the C-terminal sugar isomerasedomain of GlcN6P synthase, the recombinant GlmDTk clearly exhibited GlcN6P deaminase activity, generating Fru6P andammonia from GlcN6P. This enzyme also catalyzed the reverse reaction,the ammonia-dependent amination/isomerization of Fru6P to GlcN6P,whereas no GlcN6P synthase activity dependent on glutamine wasobserved. Kinetic analyses clarified the preference of this enzyme forthe deaminase reaction rather than the reverse one, consistent with thecatabolic function of GlmDTk . InT.kodakaraensis cells,glmDTk waspolycistronically transcribed together with upstream genes encoding anABC transporter and a downstream exo-β-glucosaminidase gene(glmATk ) within the gene cluster, and theirexpression was induced by the chitin degradation intermediate,diacetylchitobiose. The results presented here indicate thatGlmDTk is actually a GlcN6P deaminase functioningin the entry of chitin-derived monosaccharides to glycolysis in thishyperthermophile. This enzyme is the first example of an archaealGlcN6P deaminase and is a structurally novel type distinct from anypreviously known GlcN6Pdeaminase.