Crystal structure of SAM-dependent O-methyltransferase from pathogenic bacterium Leptospira interrogans

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• S-adenosylmethionine (SAM)-dependent O-methyltransferases are crucial enzymes, often involved in antibiotic biosynthesis.
• The Methyltransf_3 family contains bacterial homologues with known functions in antibiotic production.
• No bacterial protein structures from this family were previously available.

Purpose of the Study:

• To determine the crystal structure of Leptospira interrogans O-methyltransferase (LiOMT).
• To characterize the structural features of LiOMT, including its SAM-binding region and catalytic site.
• To infer the substrate and function of LiOMT based on structural and sequence analysis.

Main Methods:

• Expression and purification of LiOMT from Leptospira interrogans.
• Crystallization of LiOMT in complex with S-adenosylhomocysteine.
• X-ray crystallography to determine the 3D structure of the LiOMT-S-adenosylhomocysteine complex.
• Sequence and structural analysis.

Main Results:

• The crystal structure of LiOMT, the first from its bacterial family, was determined.
• LiOMT forms homodimers through N-terminal swapping, aiding substrate-binding site organization.
• A conserved SAM-binding region and a probable metal-dependent catalytic site were identified.
• Structural analysis suggests LiOMT acts on a phenolic derivative with a large, ring-shaped moiety.

Conclusions:

• The structure provides critical insights into the mechanism of SAM-dependent O-methyltransferases in bacteria.
• LiOMT's structural characteristics suggest a role in the biosynthesis of complex molecules, potentially antibiotics.
• This study lays the groundwork for further functional characterization and potential drug development targeting bacterial methyltransferases.