Fig. 4: A single active residue underlies functional divergence of LDS and PS from LSS in echinoderms.

a, Superpositioned homology models of sea star (P. miniata LSS), sea urchin (S. purpuratus LSS) and divergent sea cucumber OSCs (P. parvimensis LDS and P. parvimensis PS) showing variation at position 444 position near the B and/or C rings of lanosterol. Colored circles next to amino acid residues in the models represent different cyclization roles. Dashed lines represent a hydrogen bond between Y503 and H232, and numbering on B and/or C rings of lanosterol represents cationic regions. b, Structure-based sequence alignment of position 444 and its associated positions across echinoderm and holozoan OSCs. Clades are colored according to OSC product specificity. OSC sequence numbering is according to that of human LSS. Further information about the sequences used is provided in Supplementary Table 2. GoPS, G. obscuriglobus PS, Dre, Danio rerio; Branchi, Branchiostoma floridae; Amphi, Amphimedon queenslandica; Sacco, Saccoglossus kowalevskii; Helob, Helobdella robusta; Af, Asterias forbesi; Ar, Asterias rubens; Lsp, Leptasterias sp.; Hsp, Henricia sp.; Es, Echinaster spinulosus; Ap, Acanthaster plancii (COTS); Ep, Echinarachnius parma; Sg, Sphaerechinus granularis; Sc, Stichopus chloronotus. c, Complementation of an LSS-deficient yeast strain with A. japonicus PS^a wild type (WT) and mutants thereof. Yeast was spotted from stock cultures undiluted (−) and diluted tenfold and 100-fold. d,e, GC–MS profiles of yeast extracts from strains expressing A. japonicus PS^a wild type and active site mutants (d) and the bacterial OSC G. obscuriglobus PS (e). The corresponding total ion chromatograms for d,e are shown in Extended Data Figs. 8d and 9c, respectively. Standards were lanosterol, lanostadienol and parkeol.