Highly sensitive detection of M.SssI DNA methyltransferase activity using a personal glucose meter

A simple method for highly sensitive and selective detection of M.SssI CpG methyltransferase (M.SssI MTase) activity is developed, leveraging on the portability and ease of use of a personal glucose meter (PGM). Briefly, DNA-invertase conjugates are hybridized with their complementary DNA strands pre-immobilized on magnetic beads. The 5′-CCGG-3′ sequence present in the DNA duplexes serves as the recognition site for both Hpa II restriction enzyme and M.SssI MTase (5′-CG-3′). Hpa II restriction enzyme specifically cleaves at unmethylated 5′-CCGG-3′ sequence, and the invertase that remains on the methylated DNA catalyzes the hydrolysis of sucrose to glucose and fructose. It is found that the amount of glucose is proportional to the M.SssI MTase methylation activity in the range of 0.5 to 80 U/mL with a detection limit of 0.37 U/mL. Due to the specific recognition sequence present in the DNA strands, this method also shows high selectivity for M.SssI MTase. In addition, inhibition studies with 5′-azacytidine demonstrate the capability of inhibition screening using this method.