Figure 83.

Stereoview of the crystal structure of 2-azasqualene bound in the active site of squalene-hopene cyclase, showing that the ligand conformation closely matches that required for the formation of rings A–D in the squalene cyclization reaction. The reaction is initiated by general acid catalyst D376, which may be reprotonated during catalysis through a “back channel” hydrogen bond network with bulk solvent. Reprinted with permission from ref (455). Copyright 2005 Wiley-VCH.