Figure 21.

Crystal structure of ApUbiA reveals the characteristic α fold of a soluble class I terpenoid synthase adapted for function as an integral membrane protein. The cap domain (pink) encloses the hydrophobic central cavity formed by transmembrane helices (blue); aspartate-rich motifs implicated in Mg²⁺ binding are indicated. The isoprenoid substrate is also embedded in the membrane and is proposed to access the active site through a lateral portal. Reprinted with permission from ref (128). Copyright 2014 AAAS.