Structure of the photoreactive iron center of the nitrile hydratase from Rhodococcus sp. N-771. Evidence of a novel post-translational modification in the cysteine ligand.
Nitrile hydratase (NHase) from Rhodococcus sp. N-771 is a photoreactive enzyme that is inactivated by nitrosylation of the non-heme iron center and activated by photodissociation of nitric oxide (NO). To obtain structural information on the iron center, we isolated peptide complexes containing the iron center by proteolysis. When the tryptic digest of the alpha subunit isolated from the inactive form was analyzed by reversed-phase high performance liquid chromatography, the absorbance characteristic of the nitrosylated iron center was observed in the peptide fragment, Asn105-Val-Ile-Val-Cys-Ser-Leu-Cys-Ser-Cys-Thr-Ala-Trp-Pro-Ile-Leu - Gly-Leu-Pro-Pro-Thr-Trp-Tyr-Lys128. The peptide contained 0.79 mol of iron/mol of molecule as well as endogenous NO. Subsequently, by digesting the peptide with thermolysin, carboxypeptidase Y, and leucine aminopeptidase M, we found that the minimum peptide segment required for the nitrosylated iron center is the 11 amino acid residues from alphaIle107 to alphaTrp117. Furthermore, by using mass spectrometry, protein sequence, and amino acid composition analyses, we have shown that the 112th Cys residue of the alpha subunit is post-translationally oxidized to a cysteine-sulfinic acid (Cys-SO2H) in the NHase. These results indicate that the NHase from Rhodococcus sp. N-771 has a novel non-heme iron enzyme containing a cysteine-sulfinic acid in the iron center. Possible ligand residues of the iron center are discussed.
Tsujimura
M
M
Graduate School of Science and Engineering, Saitama University, Urawa, Saitama, Japan.
Dohmae
N
N
Odaka
M
M
Chijimatsu
M
M
Takio
K
K
Yohda
M
M
Hoshino
M
M
Nagashima
S
S
Endo
I
I
D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D006836:Hydro-Lyases / Q000096:biosynthesis / Q000737:chemistry*; D007501:Iron / Q000378:metabolism; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010777:Photochemistry; D011499:Protein Processing, Post-Translational; D012240:Rhodococcus / Q000201:enzymology*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013056:Spectrophotometry, Ultraviolet
D007501:Iron; D006836:Hydro-Lyases; C048831:nitrile hydratase; D003545:Cysteine