High-resolution crystal structure of manganese peroxidase: substrate and inhibitor complexes

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Manganese peroxidase (MnP) is an extracellular heme enzyme crucial for lignin degradation and oxidative stress response.
• Understanding MnP's metal-binding site is key to elucidating its catalytic mechanism and developing inhibitors.
• Previous structural data at 2.0 Å resolution provided initial insights into Mn(II) ligation.

Purpose of the Study:

• To obtain higher resolution crystal structures of MnP complexed with various metal ions.
• To elucidate the precise coordination geometry and interactions within the Mn(II)-binding site.
• To investigate the binding of other metal ions (Cd(II), Sm(III)) and potential inhibitor interactions.

Main Methods:

• X-ray crystallography to determine MnP structures at 1.45 Å resolution.
• Crystallographic analysis of MnP complexed with Mn(II), Cd(II), and Sm(III).
• Soaking experiments to study metal-ion removal and reintroduction, including oxalate treatment.

Main Results:

• A refined 1.45 Å crystal structure of MnP with Mn(II) reveals detailed Mn-binding site ligands (heme propionate, Glu35, Glu39, Asp179) and potential Glu39 protonation.
• Glycosylation at Ser336 was identified.
• Structures of MnP-inhibitor complexes were reported for the first time. Cd(II) binds with hexacoordinate and tetrahedral geometries. Sm(III) exhibits octacoordinate binding at the Mn-site, with reversible binding observed.

Conclusions:

• The high-resolution structures provide unprecedented detail of the MnP metal-binding site and its interactions.
• The study characterizes the binding of various metal ions, offering insights into substrate and inhibitor interactions.
• Reversible Sm(III) binding serves as a model for understanding the transient Mn(III) binding crucial for MnP catalysis.