Steroid biosynthesis in prokaryotes: identification of myxobacterial steroids and cloning of the first bacterial 2,3(S)-oxidosqualene cyclase from the myxobacterium Stigmatella aurantiaca

Authors

  • Helge Björn Bode,

    1. GBF – Gesellschaft für Biotechnologische Forschung, Abteilung NBI/MX, Mascheroder Weg 1, 38124 Braunschweig, Germany.
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  • Bernd Zeggel,

    1. GBF – Gesellschaft für Biotechnologische Forschung, Abteilung NBI/MX, Mascheroder Weg 1, 38124 Braunschweig, Germany.
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  • Barbara Silakowski,

    1. GBF – Gesellschaft für Biotechnologische Forschung, Abteilung NBI/MX, Mascheroder Weg 1, 38124 Braunschweig, Germany.
    2. Institut für Pharmazeutische Biologie, TU Braunschweig, Mendelssohnstrasse 1, 38106 Braunschweig, Germany.
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  • Silke C. Wenzel,

    1. GBF – Gesellschaft für Biotechnologische Forschung, Abteilung NBI/MX, Mascheroder Weg 1, 38124 Braunschweig, Germany.
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  • Hans Reichenbach,

    1. GBF – Gesellschaft für Biotechnologische Forschung, Abteilung NBI/MX, Mascheroder Weg 1, 38124 Braunschweig, Germany.
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  • Rolf Müller

    Corresponding author
    1. GBF – Gesellschaft für Biotechnologische Forschung, Abteilung NBI/MX, Mascheroder Weg 1, 38124 Braunschweig, Germany.
    2. Institut für Pharmazeutische Biologie, TU Braunschweig, Mendelssohnstrasse 1, 38106 Braunschweig, Germany.
    • For correspondence at the first address. E-mail rom@gbf.de ; Tel. (+49) 531 618 1420; Fax (+49) 531 618 1284.

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  • Present addresses: Biochemistry Department, Stanford University, CA, USA. Institut für Mikrobiologie, TU München, Weihenstephaner Berg 3, 85354 Freising, Germany.

Summary

Steroids, such as cholesterol, are synthesized in almost all eukaryotic cells, which use these triterpenoid lipids to control the fluidity and flexibility of their cell membranes. Bacteria rarely synthesize such tetracyclic compounds but frequently replace them with a different class of triterpenoids, the pentacyclic hopanoids. The intriguing mechanisms involved in triterpene biosynthesis have attracted much attention, resulting in extensive studies of squalene-hopene cyclase in bacteria and (S)-2,3-oxidosqualene cyclases in eukarya. Nevertheless, almost nothing is known about steroid biosynthesis in bacteria. Only three steroid-synthesizing bacterial species have been identified before this study. Here, we report on a variety of sterol-producing myxobacteria. Stigmatella aurantiaca is shown to produce cycloartenol, the well-known first cyclization product of steroid biosynthesis in plants and algae. Additionally, we describe the cloning of the first bacterial steroid biosynthesis gene, cas, encoding the cycloartenol synthase (Cas) of S. aurantiaca. Mutants of cas generated via site-directed mutagenesis do not produce the compound. They show neither growth retardation in comparison with wild type nor any increase in ethanol sensitivity. The protein encoded by cas is most similar to the Cas proteins from several plant species, indicating a close evolutionary relationship between myxobacterial and eukaryotic steroid biosynthesis.

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