Evolution, structure and function of the biosynthetic gene cluster of myriocin, a potent inhibitory sphingolipid

Myriocin is a fungal secondary metabolite exploited worldwide as a powerful inhibitor of sphingolipid biosynthesis through its structural similarity to sphingosine. We identify the myriocin biosynthesis gene cluster (BGC) through de novo sequencing of two producing fungi, Isaria sinclairii and Mycelia sterilia, yielding genomes of 25.2 Mb and 34.2 Mb encoding 27 and 20 secondary metabolite BGCs, respectively. BGCs #5 in I. sinclairii and #18 in M. sterilia shared the Polyketide Synthase (PKS) and alpha oxo-amine synthase (AOS) predicted for myriocin biosynthesis, with 74 % and 79 % sequence similarity, respectively. Analysis of a 2,236 fungal genome database suggests the pathway originated in the Sordariomycete ancestor, presenting in two major clades distinguished by PKS gene orientation. The placement of thermophilic M. sterilia suggests myriocin BGC acquisition through horizontal gene transfer, but its origin in I. sinclairii is ambiguous. Heterologously-expressed IsMyrA bound amino-malonate and a protein-protein docking interface were identified between the acyl carrier protein and IsMyrA. A model of PKS domain function, the roles of the PKS and AOS genes and the synteny of the myriocin biosynthetic gene cluster across 34 carrier species of Ascomycetes is presented.