A directed evolution design of a GCG-specific DNA hemimethylase

Area of Science:

• Biochemistry and Molecular Biology
• Protein Engineering and Biotechnology

Background:

• DNA cytosine-5 methyltransferases (C5-MTases) are crucial for studying DNA modification and have growing biotechnological importance.
• The HhaI C5-MTase enzyme recognizes a specific GCGC DNA sequence.

Purpose of the Study:

• To rationally design a novel C5-MTase with altered DNA sequence specificity.
• To engineer the HhaI C5-MTase to recognize GCG instead of GCGC.

Main Methods:

• Employed structure-guided rational protein design coupled with random mutagenesis and selection.
• Introduced a five-residue deletion and two arginine residues in key DNA-recognizing loops.
• Utilized DNA protection assays, bisulfite sequencing, and enzyme kinetics to evaluate variants.

Main Results:

• Successfully altered the HhaI C5-MTase specificity from GCGC to GCG.
• The best engineered variant demonstrated comparable sequence fidelity and methylation efficiency to wild-type M.HhaI.
• The designed enzyme showed superior performance in transalkylation of DNA using synthetic cofactor analogs.

Conclusions:

• The engineered C5-MTase is a valuable tool for specific DNA modification.
• This designed enzyme can generate hemimethylated CpG sites, essential for studying mammalian maintenance methyltransferases.
• Protein engineering of C5-MTases offers new avenues for biotechnological applications and epigenetics research.