A molecular dynamics examination on mutation-induced catalase activity in coral allene oxide synthase

Coral allene oxide synthase (cAOS) catalyzes the formation of allene oxides from fatty acid hydroperoxides. Interestingly, its active site differs from that of catalase by only a single residue yet is incapable of catalase activity. That is, it is unable to catalyze the decomposition of hydrogen peroxide to molecular oxygen and water. However, the single active-site mutation T66V allows cAOS to exhibit catalase activity. We have performed a series of molecular dynamics (MD) simulations in order to gain insights into the differences in substrate (8R-hydroperoxyeicosatetraenoic) and H2O2 active site binding between wild-type cAOS and the T66V mutant cAOS. It is observed that in wild-type cAOS the active site Thr66 residue consistently forms a strong hydrogen-bonding interaction with H2O2 (catalase substrate) and, importantly, with the aid of His67 helps to pull H2O2 away from the heme Fe center. In contrast, in the T66V-cAOS mutant the H2O2 is much closer to the heme's Fe center and now forms a consistent Fe···O2H2 interaction. In addition, the His67···H2O2 distance shortens considerably, increasing the likelihood of a Cpd I intermediate and hence exhibiting catalase activity.