Synthesis of Stable NAD+ Mimics as Inhibitors for the Legionella pneumophila Phosphoribosyl Ubiquitylating Enzyme SdeC

Abstract

Stable NAD⁺ analogues carrying single atom substitutions in either the furanose ring or the nicotinamide part have proven their value as inhibitors for NAD⁺ -consuming enzymes. To investigate the potential of such compounds to inhibit the adenosine diphosphate ribosyl (ADPr) transferase activity of the Legionella SdeC enzyme, we prepared three NAD⁺ analogues, namely carbanicotinamide adenosine dinucleotide (c-NAD⁺ ), thionicotinamide adenosine dinucleotide (S-NAD⁺ ) and benzamide adenosine dinucleotide (BAD). We optimized the chemical synthesis of thionicotinamide riboside and for the first time used an enzymatic approach to convert all three ribosides into the corresponding NAD⁺ mimics. We thus expanded the known scope of substrates for the NRK1/NMNAT1 enzyme combination by turning all three modified ribosides into NAD⁺ analogues in a scalable manner. We then compared the three NAD⁺ mimics side-by-side in a single assay for enzyme inhibition on Legionella effector enzyme SdeC. The class of SidE enzymes to which SdeC belongs was recently identified to be important in bacterial virulence, and we found SdeC to be inhibited by S-NAD⁺ and BAD with IC₅₀ values of 28 and 39 μM, respectively.

Keywords: ADP-ribosylation; Legionella; inhibitors; ubiquitylation.