title: Structural analysis of the substrate recognition mechanism in O-phosphoserine sulfhydrylase from the hyperthermophilic archaeon Aeropyrum pernix K1.
abstract: L-Cysteine is synthesized from O-acetyl-L-serine (OAS) and sulfide by O-acetylserine sulfhydrylase (OASS; EC 2.5.1.47) in plants and bacteria. O-phosphoserine sulfhydrylase (OPSS; EC 2.5.1.65) is a novel enzyme from the hyperthermophilic aerobic archaeon Aeropyrum pernix K1 (2003). OPSS can use OAS or O-phospho-L-serine (OPS) to synthesize L-cysteine. To elucidate the mechanism of the substrate specificity of OPSS, we analyzed three-dimensional structures of the active site of the enzyme. The active-site lysine (K127) of OPSS forms an internal Schiff base with pyridoxal 5'-phosphate. Therefore, crystals of the complexes formed by the K127A mutant with the external Schiff base of pyridoxal 5'-phosphate with either OPS or OAS were prepared and examined by X-ray diffraction analysis. In contrast to that observed for OASS, no significant difference was seen in the overall structure between the free and complexed forms of OPSS. The side chains of T152, S153, and Q224 interacted with the carboxylate of the substrates, as a previous study has suggested. The side chain of R297 has been proposed to recognize the phosphate group of OPS. Surprisingly, however, the position of R297 was significantly unchanged in the complex of the OPSS K127A mutant with the external Schiff base, allowing enough space for an interaction with OPS. The positively charged environment around the entrance of the active site including S153 and R297 is important for accepting negatively charged substrates such as OPS.
authors.affiliation: Laboratory of Molecular Biochemistry, Nagahama Institute of Bio-Science and Technology, 1266 Tamura-cho, Nagahama, Shiga 526-0829, Japan. t_nakamura@nagahama-i-bio.ac.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakamura
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Kawai
authors.forename: Kohei
authors.initials: K
authors.lastname: Kunimoto
authors.forename: Yuka
authors.initials: Y
authors.lastname: Iwasaki
authors.forename: Kaoru
authors.initials: K
authors.lastname: Nishii
authors.forename: Misumi
authors.initials: M
authors.lastname: Kataoka
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Ishikawa
mesh_terms: D041522:Aeropyrum / Q000201:enzymology* / Q000378:metabolism; D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D019757:Carbon-Oxygen Lyases / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D007700:Kinetics; D011732:Pyridoxal Phosphate / Q000737:chemistry / Q000378:metabolism; D012545:Schiff Bases / Q000737:chemistry; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D019843:Archaeal Proteins; D012545:Schiff Bases; D011732:Pyridoxal Phosphate; C503351:O-phosphoserine sulfhydrylase, Aeropyrum pernix; D019757:Carbon-Oxygen Lyases