The binding site for an inhibitor of squalene:hopene cyclase determined using photoaffinity labeling and molecular modeling.
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.
Dang
T
T
Department of Medicinal Chemistry The University of Utah 30 South 2000 East, Room 201, Salt Lake City, Utah, 84112-5820, USA.
Abe
I
I
Zheng
Y F
YF
Prestwich
G D
GD
D000345:Affinity Labels; D000595:Amino Acid Sequence; D001406:Bacillaceae / Q000201:enzymology; D001577:Benzophenones / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D020134:Catalytic Domain; D019751:Intramolecular Transferases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism
D000345:Affinity Labels; D001577:Benzophenones; D011994:Recombinant Proteins; C105726:Ro 48-8071; D019751:Intramolecular Transferases; C066630:squalene-hopene cyclase