Asymmetric DNA methylation by dimeric EcoP15I DNA methyltransferase

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• EcoP15I DNA methyltransferase (M.EcoP15I) methylates the 5'-CAGCAG-3' sequence, protecting DNA from restriction enzymes.
• M.EcoP15I is known to function as a dimer, but the role of dimerization in its catalytic mechanism is unclear.
• Understanding M.EcoP15I dimerization is crucial for elucidating its DNA methylation mechanism.

Purpose of the Study:

• To investigate the role of M.EcoP15I dimerization in its DNA methylation activity.
• To characterize the biochemical properties of a monomeric M.EcoP15I mutant.

Main Methods:

• Engineering of a stable monomeric form of M.EcoP15I.
• Biochemical assays to assess DNA binding and methylation activity of monomeric and dimeric M.EcoP15I.
• Analysis of cofactor binding (AdoMet, Mg2+) in the monomeric form.

Main Results:

• The monomeric M.EcoP15I can bind single-stranded DNA (ssDNA) with the recognition sequence but cannot methylate it.
• Monomeric M.EcoP15I retains intact AdoMet and Mg2+ binding motifs.
• Optimal double-stranded DNA (dsDNA) binding, essential for methylation, is dependent on M.EcoP15I dimerization.

Conclusions:

• Dimerization is essential for M.EcoP15I's ability to bind dsDNA and catalyze methylation.
• M.EcoP15I exhibits a unique subunit organization for its methylation reaction.
• These findings provide new insights into the mechanism of DNA methylation by M.EcoP15I.