title: The archaeon Pyrococcus horikoshii possesses a bifunctional enzyme for formaldehyde fixation via the ribulose monophosphate pathway.
abstract: Pyrococcus horikoshii OT3, a hyperthermophilic and anaerobic archaeon, was found to have an open reading frame (PH1938) whose deduced amino acid sequence of the N-terminal and C-terminal halves showed significant similarity to two key enzymes of the ribulose monophosphate pathway for formaldehyde fixation in methylotrophic bacteria, 3-hexulose-6-phosphate synthase (HPS) and 6-phospho-3-hexuloisomerase (PHI), respectively. The organism constitutively produced the encoded protein and exhibited activity of the sequential HPS- and PHI-mediated reactions in a particulate fraction. The full-length gene encoding the hybrid enzyme, the sequence corresponding to the HPS region, and the sequence corresponding to the PHI region were expressed in Escherichia coli and were found to produce active enzymes, rHps-Phi, rHps, or rPhi, respectively. Purified rHps-Phi and rHps were found to be active at the growth temperatures of the parent strain, but purified rPhi exhibited significant susceptibility to heat, suggesting that thermostability of the PHI moiety of the bifunctional enzyme (rHps-Phi) resulted from fusion with HPS. The bifunctional enzyme catalyzed the sequential reaction much more efficiently than a mixture of rHps and rPhi. These and other biochemical characterizations of the PH1938 gene product suggest that the ribulose monophosphate pathway plays a significant role in the archaeon under extreme environmental conditions.
authors.affiliation: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kitashirakawa Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Izumi
authors.initials: I
authors.lastname: Orita
authors.forename: Hiroya
authors.initials: H
authors.lastname: Yurimoto
authors.forename: Reiko
authors.initials: R
authors.lastname: Hirai
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Kawarabayasi
authors.forename: Yasuyoshi
authors.initials: Y
authors.lastname: Sakai
authors.forename: Nobuo
authors.initials: N
authors.lastname: Kato
mesh_terms: D000446:Aldehyde-Lyases / Q000235:genetics / Q000378:metabolism*; D019747:Aldose-Ketose Isomerases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli; D005557:Formaldehyde / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D010429:Pentoses / Q000378:metabolism; D043902:Pyrococcus horikoshii / Q000201:enzymology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D013696:Temperature
chemical_list: D019843:Archaeal Proteins; D010429:Pentoses; D011993:Recombinant Fusion Proteins; D005557:Formaldehyde; C100182:ribulose; D000446:Aldehyde-Lyases; C021355:hexose phosphate synthetase; D019747:Aldose-Ketose Isomerases; C023918:phospho-3-hexuloisomerase