δ10(E)-sphingolipid desaturase involved in fusaruside mycosynthesis and stress adaptation in Fusarium graminearum

Abstract

Sphingolipids are biologically important and structurally distinct cell membrane components. Fusaruside (1) is a 10,11-unsaturated immunosuppressive fungal sphingolipid with medical potentials for treating liver injury and colitis, but its poor natural abundance bottlenecks its druggability. Here, fusaruside is clarified biosynthetically, and its efficacy-related 10,11-double bond can be generated under the regioselective catalysis of an unprecedented δ 10(E)-sphingolipid desaturase (δ 10(E)-SD). δ 10(E)-SD shares 17.7% amino acid sequence similarity with a C9-unmethylated δ 10-sphingolipid desaturase derived from a marine diatom, and 55.7% with δ 8(E)-SD from Fusarium graminearum. Heterologous expression of δ 10(E)-SD in Pichia pastoris has been established to facilitate a reliable generation of 1 through the δ 10(E)-SD catalyzed desaturation of cerebroside B (2), an abundant fungal sphingolipid. Site directed mutageneses show that the conserved histidines of δ 10 (E)-SD are essential for the 10,11-desaturation catalysis, which is also preconditioned by the C9-methylation of the substrate. Moreover, δ 10 (E)-SD confers improved survival and faster growth to fungal strains at low temperature and high salinity, in parallel with to higher contents of 1 in the mycelia. Collectively, the investigation describes a new δ 10(E)-sphingolipid desaturase with its heterologous expression fundamentalizing a biotechnological supply of 1, and eases the follow-up clarification of the immunosuppression and stress-tolerance mechanism.