Snapshots of C‐S cleavage in Egt2 reveals substrate specificity and reaction mechanism

Abstract

Ergothioneine is a thiol histidine derivative with a significant potential for biomedical applications. The sulfur incorporation strategy in ergothioneine biosynthesis differs from other well characterized transsulfuration reactions. A combination of a mononuclear non‐heme iron dependent 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 the ergothioneine biosynthesis pathway. In this study, we have structurally and mechanistically characterized a PLP‐dependent C‐S lyase Egt2 (from Neurospora crassa), which mediates the sulfoxide C‐S bond cleavage in the ergothioneine biosynthesis pathway. The 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 acid 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.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.