The Fe-type nitrile hydratase from Rhodococcus equi TG328-2 forms an alpha-activator protein complex

Area of Science:

• Biochemistry
• Enzymology
• Protein complex characterization

Background:

• Nitrile hydratases (NHases) are crucial enzymes in nitrile metabolism.
• The α(ɛ) protein complex from Rhodococcus equi TG328-2 (ReNHase) was identified as a potential component of NHase.
• The precise role of the α(ɛ) complex and its subunits in NHase activity and metallocenter assembly remained unclear.

Purpose of the Study:

• To investigate the functional reconstitution of the ReNHase α(ɛ) protein complex.
• To determine the roles of the β-subunit, iron, GTP, and reducing agents in NHase activity.
• To elucidate the contribution of the α(ɛ) complex to NHase metallocenter assembly.

Main Methods:

• Purification and characterization of the ReNHase α(ɛ) protein complex.
• Enzyme activity assays using acrylonitrile as substrate.
• Mass spectrometry (MALDI-TOF) to confirm complex formation.
• In vitro reconstitution assays with varying components (β-subunit, Fe(II), GTP, TCEP).

Main Results:

• The isolated α(ɛ) complex showed no NHase activity.
• Reconstitution of NHase activity required the addition of the β-subunit and Fe(II).
• GTP and the reducing agent TCEP significantly enhanced the reconstituted enzyme's catalytic efficiency (kcat).
• In vitro formation of the α(ɛ) complex was demonstrated, and its activity was modulated by GTP and TCEP.

Conclusions:

• The ReNHase β-subunit is essential for reconstituting nitrile hydratase activity.
• GTP and reducing conditions play important regulatory roles in the enzyme's function.
• The α(ɛ) protein complex is integral to NHase metallocenter assembly and function.