Development of a Suicide Inhibition Based Protein Labeling (SIBLing) Strategy for Nicotinamide N-methyltransferase.

Nicotinamide N-methytransferase (NNMT) catalyzes the S-adenosyl-L-methionine (SAM)-dependent methylation of nicotinamide (NAM) to form N-methylnicotinamide (Me-NAM). This enzyme detoxifies xenobiotics and regulates NAD+ biosynthesis. Additionally, NNMT is overexpressed in various cancers. Herein, we describe the first NNMT-targeted suicide substrates. These compounds, which include 4-chloropyridine and 4-chloronicotinamide, exploit the broad substrate scope of NNMT; methylation of the pyridine nitrogen enhances the electrophilicity of the C4 position, thereby promoting an aromatic nucleophilic substitution by C159, a non-catalytic cysteine. Based on this activity, we developed a suicide inhibition-based protein labeling (SIBLing) strategy using an alkyne-substituted 4-chloropyridine that selectively labels NNMT in vitro and in cells. In total, this study describes the first NNMT-directed activity-based probes.