Inhibition of a prokaryotic GH78 α-l-rhamnosidase by synthetic pyrrolidines compared to a eukaryotic α-l-rhamnosidase from Penicillium decumbens

This study presents the first evaluation of diverse iminosugars as inhibitors of a prokaryotic GH78 α- l -rhamnosidase. The pyrrolidine derivatives acted as enzyme competitive inhibitors. The most effective inhibitors were the N -( p -iodo)benzyl derivatives of 1,4-dideoxy-1,4-imino- l -lyxitol and 1,4,6-trideoxy-1,4-imino- l -mannitol (6-deoxy- l -DIM), exhibiting IC 50 values of 2–4 μM and K i values of 1.3–2.1 μM at pH 6.5, the enzyme's optimal pH. A moderate decrease in the inhibitory potency was observed at pH 5.5, suggesting that the ionization state of the inhibitors affects their interaction with the enzyme. Evaluation of 10 glycosidase activities revealed that the most potent compound, N -( p -iodobenzyl)-6-deoxy- l -DIM 9 , is a highly selective α- l -rhamnosidase inhibitor. None of these potent α- l -rhamnosidase inhibitors had previously been shown toxic for non-malignant human fibroblast cells (HFF-BJ) at a concentration of 50 μM, suggesting their potential for biomedical exploitation. Comparison with the data published for a eukaryotic α- l -rhamnosidase from Penicillium decumbens, the only α- l -rhamnosidase studied so far with regard to inhibition, showed that several pyrrolidines exhibit similar or slightly enhanced inhibition of the bacterial enzyme, indicating structural similarities of the active sites in the bacterial and eukaryotic α- l -rhamnosidases.