Protostadienol synthase from Aspergillus fumigatus: functional conversion into lanosterol synthase

Biochem Biophys Res Commun. 2010 Jan 1;391(1):899-902. doi: 10.1016/j.bbrc.2009.11.160. Epub 2009 Nov 29.


Oxidosqualene:protostadienol cyclase (OSPC) from the fungus Aspergillus fumigatus, catalyzes the cyclization of (3S)-2,3-oxidosqualene into protosta-17(20)Z,24-dien-3beta-ol which is the precursor of the steroidal antibiotic helvolic acid. To shed light on the structure-function relationship between OSPC and oxidosqualene:lanosterol cyclase (OSLC), we constructed an OSPC mutant in which the C-terminal residues (702)APPGGMR(708) were replaced with (702)NKSCAIS(708), as in human OSLC. As a result, the mutant no longer produced the protostadienol, but instead efficiently produced a 1:1 mixture of lanosterol and parkeol. This is the first report of the functional conversion of OSPC into OSLC, which resulted in a 14-fold decrease in the V(max)/K(M) value, whereas the binding affinity for the substrate did not change significantly. Homology modeling suggested that stabilization of the C-20 protosteryl cation by the active-site Phe701 through cation-pi interactions is important for the product outcome between protostadienol and lanosterol.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Aspergillus fumigatus / enzymology*
  • Aspergillus fumigatus / genetics
  • Cyclization
  • Fusidic Acid / analogs & derivatives
  • Fusidic Acid / biosynthesis
  • Intramolecular Transferases / chemistry
  • Intramolecular Transferases / genetics
  • Intramolecular Transferases / metabolism*
  • Molecular Sequence Data
  • Squalene / analogs & derivatives
  • Squalene / chemistry
  • Squalene / metabolism
  • Triterpenes / chemistry
  • Triterpenes / metabolism


  • Triterpenes
  • protosta-13(17),24-dien-3beta-ol
  • oxidosqualene
  • Fusidic Acid
  • Squalene
  • Intramolecular Transferases
  • lanosterol synthase
  • helvolic acid