Dang T, Abe I, Zheng YF, Prestwich GD. The binding site for an inhibitor of squalene:hopene cyclase determined using photoaffinity labeling and molecular modeling.
CHEMISTRY & BIOLOGY 1999;
6:333-41. [PMID:
10375539 DOI:
10.1016/s1074-5521(99)80045-3]
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Abstract
BACKGROUND
The squalene:hopene cyclases (SHCs) are bacterial enzymes that convert squalene into hopanoids, a function analogous to the action of oxidosqualene cyclases (OSCs) in eukaryotic steroid and triterpenoid biosynthesis. We have identified the binding site for a selective, potent, photoactivatable inhibitor of an SHC.
RESULTS
SHC from Alicyclobacillus acidocaldarius was specifically labeled by [3H]Ro48-8071, a benzophenone-containing hypocholesteremic drug. Edman degradation of a peptide fragment of covalently modified SHC confirmed that Ala44 was specifically modified. Molecular modeling, using X-ray-derived protein coordinates and a single point constraint for the inhibitor, suggested several geometries by which Ro48-8071 could occupy the active site.
CONCLUSIONS
A covalent complex of a potent inhibitor with a squalene cyclase has been characterized. The amino acid modification and molecular modeling suggest that Ro48-8071 binds at the junction between the central cavity and substrate entry channel, therefore inhibiting access of the substrate to the active site.
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