Lysine-cysteine NOS bonds: Difference between revisions
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This is a summary of the observations supporting the NOS bond<ref name="wensien2021" />. [[6zx4]] (oxidized form, NOS present, enzyme inactive) has a [[resolution]] of 0.96 Å, with a better than average [[Rfree|R<sub>free</sub>]] of 0.136. ''Neisseria gonorrhoeae'' transaldolase has 3 cysteines (no disulfide bonds). It does not form disulfide-linked oligomers. Each Cys was individually mutated to Ser. Only the mutation Cys38Ser abolished redox control, producing a constitutively active enzyme. | This is a summary of the observations supporting the NOS bond<ref name="wensien2021" />. [[6zx4]] (oxidized form, NOS present, enzyme inactive) has a [[resolution]] of 0.96 Å, with a better than average [[Rfree|R<sub>free</sub>]] of 0.136. ''Neisseria gonorrhoeae'' transaldolase has 3 cysteines (no disulfide bonds). It does not form disulfide-linked oligomers. Each Cys was individually mutated to Ser. Only the mutation Cys38Ser abolished redox control, producing a constitutively active enzyme. | ||
Electron density for an unidentified atom appeared between the sidechain nitrogen of Lys8 and the sulfur of Cys38 for several crystals under nonreducing conditions, as well as in data from a low-dose non-synchrotron source, arguing against a radiation damage artifact. Competitive refinements indicated that the unidentified atom was oxygen, rather than carbon. | Electron density for an unidentified atom appeared between the sidechain nitrogen of Lys8 and the sulfur of Cys38 for several crystals under nonreducing conditions, as well as in data from a low-dose non-synchrotron source, arguing against a radiation damage artifact. Competitive refinements indicated that the unidentified atom was oxygen, rather than carbon. Mass spectrometry analysis was consistent with this conclusion. | ||
In crystals of reduced (active) enzyme, the Lys8-O-Cys38 bridge was absent. However, electron density near the Cys38 sulfur was consistent with molecular oxygen O<sub>2</sub>. Molecular oxygen was absent in this position in the oxidized (active) enzyme. | In crystals of reduced (active) enzyme, the Lys8-O-Cys38 bridge was absent. However, electron density near the Cys38 sulfur was consistent with molecular oxygen O<sub>2</sub>. Molecular oxygen was absent in this position in the oxidized (active) enzyme. | ||