Squalene cyclase (SQCY) domain subgroup 1; found in class II terpene cyclases that have an alpha 6 - alpha 6 barrel fold. Squalene cyclase (SQCY) and 2,3-oxidosqualene cyclase (OSQCY) are integral membrane proteins that catalyze a cationic cyclization cascade converting linear triterpenes to fused ring compounds. This group contains bacterial SQCY which catalyzes the convertion of squalene to hopene or diplopterol and eukaryotic OSQCY which transforms the 2,3-epoxide of squalene to compounds such as, lanosterol in mammals and fungi or, cycloartenol in plants. Deletion of a single glycine residue of Alicyclobacillus acidocaldarius SQCY alters its substrate specificity into that of eukaryotic OSQCY. Both enzymes have a second minor domain, which forms an alpha-alpha barrel that is inserted into the major domain.
Jiyao W et al.(2023). "The conserved domain database in 2023.",