Dual Stabilization of S-Adenosylmethionine for Enzymatic DNA Labeling

ABSTRACT S-Adenosyl-L-methionine (AdoMet) analogues are powerful tool for site-specific biomolecular labeling via methyltransferase (MTase) catalyzed transfer reactions. However, their utility is often limited by poor chemical stability under enzymatic reaction conditions. Here, we report a new class of stabilized AdoMet analogues featuring a conformationally constrained proline side chain in place of homoalanine. This substitution inhibits intramolecular cyclization, a major decomposition pathway. Combination with selenonium modification, which suppresses depurination, yields analogues with up to a 90-fold increase half-life relative to AdoMet. These cofactors retain activity with DNA MTases, and allow sequence-specific labeling of plasmid DNA using both two-step and single-step approaches with fluorescent dyes.