title: X-ray crystal structure of a mutant assimilatory nitrite reductase that shows sulfite reductase-like activity.
abstract: Assimilatory nitrite reductase (aNiR) reduces nitrite ions (NO(2)(-)) to ammonium ions (NH(4)(+)), whereas assimilatory sulfite reductase reduces sulfite (SO(3)(2-)) to hydrogen sulfide (HS(-)). Although aNiR can also reduce SO(3)(2-), its activity is much lower than when NO(2)(-) is reduced as the substrate. To increase the SO(3)(2-)-reduction activity of aNiR, we performed a N226K mutation of Nii3, a representative aNiR. The resulting Nii3-N226K variant could bind non-native targets, SO(3)(2-), and HCO(3)(-), in addition to its native target, i.e., NO(2)(-). We have determined the high-resolution structure of Nii3-N226K in its apo-state and in complex with SO(3)(2-), NO(2)(-), and HCO(3)(-). This analysis revealed conformational changes of Lys226 and the adjacent Lys224 upon binding of SO(3)(2-), but not NO(2)(-)In contrast, HCO(3)(-) binding induced a conformational change at Arg179. After replacing Asn226 with a positively charged Lys, aNiR showed affinity for several anions. A comparison of all ligand-bound structures for Nii3-N226K revealed that structural changes in the active site depend on the size of the substrate.
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, 1-3-1, Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
authors.forename: Shogo
authors.initials: S
authors.lastname: Nakano
authors.forename: Misa
authors.initials: M
authors.lastname: Takahashi
authors.forename: Atsushi
authors.initials: A
authors.lastname: Sakamoto
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Morikawa
authors.forename: Katsuo
authors.initials: K
authors.lastname: Katayanagi
mesh_terms: D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D009154:Mutation; D050898:Nitrite Reductase (NAD(P)H) / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D013447:Sulfites / Q000737:chemistry / Q000378:metabolism*
chemical_list: D013447:Sulfites; D010088:Oxidoreductases; D050898:Nitrite Reductase (NAD(P)H)