Squalene-hopene cyclase: final deprotonation reaction, conformational analysis for the cyclization of (3R,S)-2,3-oxidosqualene and further evidence for the requirement of an isopropylidene moiety both for initiation of the polycyclization cascade and for the formation of the 5-membered E-ring

• Published in: Organic & biomolecular chemistry Vol. 2; no. 10; pp. 1456 - 1470
• Main Authors: Hoshino, T, Nakano, S, Kondo, T, Sato, T, Miyoshi, A
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 21.05.2004
• Subjects: Alkenes - chemistry; Binding Sites - physiology; Bridged-Ring Compounds - chemistry; Bridged-Ring Compounds - metabolism; Chemistry; Chemistry, Organic; Chromatography, Gas; Cyclization; Deuterium - chemistry; Gram-Positive Bacteria - enzymology; Intramolecular Transferases - chemistry; Intramolecular Transferases - metabolism; Magnetic Resonance Spectroscopy; Models, Chemical; Models, Molecular; Molecular Conformation; Molecular Structure; Physical Sciences; Polycyclic Compounds - chemistry; Polycyclic Compounds - metabolism; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Science & Technology; Squalene - analogs & derivatives; Squalene - chemistry; Squalene - metabolism; Stereoisomerism; Structure-Activity Relationship; Triterpenes - chemistry; Triterpenes - metabolism; Water - chemistry; CYCLOARTENOL SYNTHASE; HOPANOID BIOSYNTHESIS; ENZYMATIC CYCLIZATION; FUNCTIONAL-ANALYSIS; CELL-FREE SYSTEM; ALICYCLOBACILLUS-ACIDOCALDARIUS; NONSPECIFIC BIOSYNTHESIS; LANOSTEROL SYNTHASE; SITE-DIRECTED MUTAGENESIS; OXIDOSQUALENE CYCLASE
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/b401172d

To provide insight into the polycyclization mechanism of squalene by squalene-hopene cyclase (SHC) from Alicyclobacilus acidocaldarius, some analogs of nor- and bisnorsqualenes were synthesized including the deuterium-labeled squalenes and incubated with the wild-type SHC, leading to the following inferences. (1) The deprotonation reaction for the introduction of the double bond of the hopene skeleton occurs exclusively from the Z-methyl group on the terminal double bond of squalene. (2) 3R-Oxidosqualene was folded in a boat conformation for the A-ring construction, while the 3S-form was in a chair structure. (3) The terminal two methyl groups are indispensable both for the formation of the 5-membered E-ring of the hopene skeleton and for the initiation of the polycyclization cascade, but the terminal Z-methyl group has a more crucial role for the construction of the 5-membered E-ring than the E-methyl group. (4) Some of the novel terpene skeletons, 36, 37, 39 and 40, were created from the analogs employed in this investigation.