Use of Metallopeptide Based Mimics Demonstrates That the Metalloprotein Nitrile Hydratase Requires Two Oxidized Cysteinates for Catalytic Activity
Nitrile hydratases (NHases) are non-heme Fe{sup III} or non-corrin Co{sup III} containing metalloenzymes that possess an N{sub 2}S{sub 3} ligand environment with nitrogen donors derived from amidates and sulfur donors derived from cysteinates. A closely related enzyme is thiocyanate hydrolase (SCNase), which possesses a nearly identical active-site coordination environment as CoNHase. These enzymes are redox inactive and perform hydrolytic reactions; SCNase hydrolyzes thiocyanate anions while NHase converts nitriles into amides. Herein an active CoNHase metallopeptide mimic, [Co{sup III}NHase-m1] (NHase-m1 = AcNH-CCDLP-CGVYD-PA-COOH), that contains Co{sup III} in a similar N{sub 2}S{sub 3} coordination environment as CoNHase is reported. [Co{sup III}NHase-m1] was characterized by electrospray ionization-mass spectrometry (ESI-MS), gel-permeation chromatography (GPC), Co K-edge X-ray absorption spectroscopy (Co-S: 2.21 {angstrom}; Co-N: 1.93 {angstrom}), vibrational, and optical spectroscopies. We find that [Co{sup III}NHase-m1] will perform the catalytic conversion of acrylonitrile into acrylamide with up to 58 turnovers observed after 18 h at 25 C (pH 8.0). FTIR data used in concert with calculated vibrational data (mPWPW91/aug-cc-TZVPP) demonstrates that the active form of [Co{sup III}NHase-m1] has a ligated SO{sub 2} (? = 1091 cm{sup -1}) moiety and a ligated protonated SO(H) (? = 928 cm{sup -1}) moiety; when only one oxygenated cysteinate ligand (i.e., a mono-SO{sub 2} coordination motif) or the bis-SO{sub 2} coordination motif are found within [Co{sup III}NHase-m1] no catalytic activity is observed. Calculations of the thermodynamics of ligand exchange (B3LYP/aug-cc-TZVPP) suggest that the reason for this is that the SO{sub 2}/SO(H) equatorial ligand motif promotes both water dissociation from the Co{sup III}-center and nitrile coordination to the Co{sup III}-center. In contrast, the under- or overoxidized motifs will either strongly favor a five coordinate Co{sup III}-center or strongly favor water binding to the Co{sup III}-center over nitrile binding.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- DOE - OFFICE OF SCIENCE
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1019913
- Report Number(s):
- BNL-95759-2011-JA; INOCAJ; TRN: US201115%%549
- Journal Information:
- Inorganic Chemistry, Vol. 49, Issue 19; ISSN 0020-1669
- Country of Publication:
- United States
- Language:
- English
Similar Records
Sequential Oxidations of Thiolates and the Cobalt Metallocenter in a Synthetic Metallopeptide: Implications for the Biosynthesis of Nitrile Hydratase
Metallopeptide Based Mimics with Substituted Histidines Approximate a Key Hydrogen Bonding Network in the Metalloenzyme Nickel Superoxide Dismutase
Related Subjects
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
ABSORPTION SPECTROSCOPY
ACRYLAMIDE
ACRYLONITRILE
AMIDES
ANIONS
CHROMATOGRAPHY
DISSOCIATION
ENZYMES
HYDROLASES
ION EXCHANGE
LIGANDS
METALLOPROTEINS
NITRILES
NITROGEN
SPECTROSCOPY
SULFUR
THERMODYNAMICS
THIOCYANATES
national synchrotron light source