Sterol phylogenesis and algal evolution

W. David Nes, Robert A. Norton, Farrist G. Crumley, Sanford J. Madigan, Eugene R. Katzt

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The stereochemistry of several sterol precursors and end products synthesized by two fungal-like microorganisms Prototheca wickerhamii (I) and Dictyostelium discoideum (II) have been determined by Chromatographic (TLC, GLC, and HPLC) and spectral (UV, MS, and 1H NMR) methods. From I and II the following sterols were isolated from the cells: cycloartenol, cyclolaudenol, 24(28)-methylenecycloartanol, ergosterol, protothecasterol, 4α-methylergostanol, 4α-methylclionastanol, clionastanol, 24β-ethylcholesta-8,22-enol, and dictyosterol. In addition, the mechanism of C-24 methylation was investigated in both organisms by feeding to I [2-3(H]lanosterol, [2-3H]cycloartenol, [24-3H]lanosterol, and [methyl-2H3]methionine and by feeding to II [methyl2H3]methionine. The results demonstrate that the 24β configuration is formed by different alkylation routes in I and II. The Δ25(27) route operates in I while the Δ24(28) route operates in II. Based on what is known in the literature regarding sterol distribution and phylogenesis together with our findings that the stereochemical outcome of squalene oxide cyclization leads to the production of cycloartenol rather than lanosterol (characteristic of the fungal genealogy) and the chirality of the C-24 alkyl group is similar in the two nonphotosv nthetic microbes (β oriented), we conclude that Prototheca is an apoplastic Chlorella (i.e., an alga) and that Dictyostelium as well as the other soil amoebae that synthesize cycloartenol evolved from algal rather than fungal ancestors.

Original languageEnglish
Pages (from-to)7570-7573
Number of pages4
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number19
StatePublished - 1990


  • Alkylation mechanisms
  • Dictyostelium discoideum
  • Ergosterol
  • H NMR
  • Prototheca wickerhamii


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