Identification of S-1-propenyl-L-cysteine as the catalytic product of AfGGT1 and a key intermediate in isoalliin biosynthesis in Allium fistulosum. L

Abstract

Our findings reveal that pyruvic acid content is generally higher in Allium fistulosum than in A. cepa. In A. fistulosum, the bulbs contain more pyruvic acid than the leaves, while in A. cepa, the inner bulb layers exhibit higher levels compared to the outer layers. We demonstrate that A. fistulosum γ-glutamyl transpeptidase 1 (AfGGT1) catalyzes the production of S-1-propenyl-L-cysteine from γ-glutamyl-S-1-propenylcysteine, whereas AfGGT2 and AfGGT3 lack catalytic activity. In natural populations of A. fistulosum, AfGGT1 expression shows a strong positive correlation with pyruvic acid content (R2 = 0.6976). The optimal catalytic conditions for AfGGT1 are pH 7 and 37 °C, with a Km value of 0.2686 mM under these conditions. Molecular docking studies further reveal distinct substrate-binding conformations among AfGGT1, AfGGT2, and AfGGT3, highlighting functional divergence within the enzyme family.

Keywords

• Allium crops
• Pungency
• γ-Glutamyl transpeptidase
• Catalysis
• S-1-propenyl-L-cysteine