Nucleoside-Driven Specificity of DNA Methyltransferase

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Bacterial DNA methyltransferases play crucial roles in DNA modification.
• Understanding cofactor binding specificities is key to enzyme engineering.
• S-adenosyl-l-methionine (SAM) is the canonical cofactor, but novel analogues are being explored.

Purpose of the Study:

• To investigate the adenosine binding specificities of Taq methyltransferase (M.TaqI) and HhaI methyltransferase (M.HhaI).
• To compare the cofactor binding pockets and dynamics of M.TaqI and M.HhaI.
• To explore the potential for designing unnatural S-nucleobase-l-methionine (SNM) analogues for methyltransferase engineering.

Main Methods:

• Experimental determination of cofactor binding specificities using novel SNMs (guanosyl, cytidyl, uridyl).
• Analysis of protein dynamics to corroborate experimental findings.
• Assessment of catalytically productive methylation by M.HhaI with various SNMs.

Main Results:

• M.TaqI and M.HhaI exhibit similar cofactor binding pocket structures but different specificities for SNMs.
• M.TaqI's specificity is driven by tight binding to the nucleoside part of SAM.
• M.HhaI's flexible nucleoside chain allows acceptance of diverse bases, enabling productive methylation with all tested SNMs.

Conclusions:

• The distinct cofactor binding mechanisms of M.TaqI and M.HhaI explain their differential SNM specificities.
• M.HhaI's adaptability opens avenues for creating novel SNM analogues.
• This study provides a foundation for engineering methyltransferase cofactors through rational design of unnatural SNM analogues.