Fig. 3. Alignment of PKZILLA PKS modules with the proposed prymnesin biosynthetic precursor.

(A) Structure of the pre-prymnesin biosynthetic precursor (PPBP) inferred from retrobiosynthetic analysis of a structurally compatible poly-epoxide cyclization cascade from the prymnesin-1 aglycone (PA) (16), and its end-to-end alignment with the assembly line modules of the PKZILLA-1/-2 gigasynthase. Select hypothesized reactions are called out in subpanels (B, C, D). See fig S20 for further detail.