Structural highlights
Publication Abstract from PubMedAssimilatory nitrite reductase (aNiR) reduces nitrite ions (NO$\rm{{_{2}^{-}}}$) to ammonium ions (NH$\rm{{_{4}^{+}}}$), whereas assimilatory sulfite reductase reduces sulfite (SO$\rm{{_{3}^{2-}}}$) to hydrogen sulfide (HS(-) ). Although aNiR can also reduce SO$\rm{{_{3}^{2-}}}$, its activity is much lower than when NO$\rm{{_{2}^{-}}}$ is reduced as the substrate. To increase the SO$\rm{{_{3}^{2-}}}$-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$\rm{{_{3}^{2-}}}$, and HCO$\rm{{_{3}^{-}}}$, in addition to its native target, i.e., NO$\rm{{_{2}^{-}}}$. We have determined the high-resolution structure of Nii3-N226K in its apo-state and in complex with SO$\rm{{_{3}^{2-}}}$, NO$\rm{{_{2}^{-}}}$, and HCO$\rm{{_{3}^{-}}}$. This analysis revealed conformational changes of Lys226 and the adjacent Lys224 upon binding of SO$\rm{{_{3}^{2-}}}$, but not NO$\rm{{_{2}^{-}}}$. In contrast, HCO$\rm{{_{3}^{-}}}$ 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. X-ray crystal structure of a mutant assimilatory nitrite reductase that shows sulfite reductase-like activity.,Nakano S, Takahashi M, Sakamoto A, Morikawa H, Katayanagi K Chem Biodivers. 2012 Sep;9(9):1989-99. doi: 10.1002/cbdv.201100442. PMID:22976986[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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