Shu Wang (Class of ’16), Anxhela Dhembi (Class of ’17), Huijue Lyu (Class of ’19)
Snapshots of C-S Cleavage in Egt2 Reveals Substrate Specificity and Reaction Mechanism, Irani, S.; Naowarojna, N.; Tang, Y.; Kathuria, K. R.; Wang, S.; Dhembi, A.; Lee, N.; Yan, W.; Lyu, H.; Costello, C. E.; Liu, P.; Zhang, Y. J., Cell Chemical Biology 2018, 25 (5), 519-529.e4.
Sulfur incorporation in the biosynthesis of ergothioneine, a histidine thiol derivative, differs from other well-characterized transsulfurations. A combination of a mononuclear non-heme iron enzyme-catalyzed oxidative C-S bond formation and a subsequent pyridoxal 5′-phosphate (PLP)-mediated C-S lyase reaction leads to the net transfer of a sulfur atom from a cysteine to a histidine. In this study, we structurally and mechanistically characterized a PLP-dependent C-S lyase Egt2, which mediates the sulfoxide C-S bond cleavage in ergothioneine biosynthesis. A cation-π interaction between substrate and enzyme accounts for Egt2’s preference of sulfoxide over thioether as a substrate. Using mutagenesis and structural biology, we captured three distinct states of the Egt2 C-S lyase reaction cycle, including a labile sulfenic intermediate captured in Egt2 crystals. Chemical trapping and high-resolution mass spectrometry were used to confirm the involvement of the sulfenic acid intermediate in Egt2 catalysis.