Structure-function relationships in fungal large-subunit catalases

Area of Science:

• Biochemistry and Molecular Biology
• Enzymology
• Structural Biology

Background:

• Neurospora crassa possesses two large-subunit catalases, CAT-1 and CAT-3, with distinct cellular associations and induction patterns.
• Understanding the structure-function relationships of these catalases is crucial for elucidating their roles in cellular processes.

Purpose of the Study:

• To determine the crystal structure of CAT-3 and compare it with the known CAT-1 structure.
• To elucidate the structure-function relationships governing the kinetics of these large-subunit catalases.

Main Methods:

• X-ray crystallography was used to determine the three-dimensional structure of CAT-3.
• Comparative structural analysis was performed between CAT-1 and CAT-3 structures.
• Kinetic analysis of hydrogen peroxide saturation was conducted for both enzymes.

Main Results:

• Both CAT-1 and CAT-3 exhibit biphasic hydrogen peroxide saturation kinetics, indicating two active sites with different affinities.
• CAT-1 possesses unique structural features including a channel constriction, a covalent bond involving tyrosine, and oxidized pyrrole ring III.
• CAT-3 shares the channel constriction but lacks the covalent bond and pyrrole oxidation, featuring an occupied central cavity and an electron relay mechanism for its functional tyrosine.

Conclusions:

• CAT-3 and CAT-1 represent a distinct functional group of catalases with unique structural characteristics.
• The identified structural differences, particularly in the active site and channel, contribute to the observed similar kinetic properties.
• This research provides insights into the structural basis of catalase activity and potential regulatory mechanisms.