Page 125 - Cascade_Biocatalysis_Integrating_Stereoselective_and_Environmentally_Friendly_Reactions

5.2 Physiological Cascade Reactions Involving P450s 101

CYP701A3 CYP701A3
H 19 H 19 H
HO HO
OH
ent-Kaurene ent-Kaurenol ent-Kaurendiol

O
H 2
non-enzymatic

CYP88A CYP701A3
7
H OH 19 H 19 H
HO HO H
O O O
ent-7α-Hydroxykaurenoic acid ent-Kaurenoic acid ent-Kaurenal

CYP88A

CYP88A
7 7
H O H O
HO H HO
O O HO
GA 12 -aldehyde GA 12

Scheme 5.12 Multistep oxidations of ent-kaurene toward gibberellin 12 (GA ) catalyzed by
12
CYP701A3 and CYP88A enzymes.

acid, yielding gibberellin 12 when expressed in yeast [51]. CYP88A was
named ent-kaurenoic acid oxidase. Thus, it was suggested that six steps in
gibberellin phytohormone biosynthesis from ent-kaurene via ent-kaurenoic acid
to gibberellins can be catalyzed by two P450s in A. thaliana. As described
above, the ent-kaurene oxidase CYP701A3 mediates three steps of oxidation at
the C19 position yielding ent-kaurenoic acid, which is subsequently used as
substrate by ent-kaurenoic acid oxidase (CYP88A) catalyzing the consecutive
three-step oxidation at the C7 position forming the final product gibberellin 12
(Scheme 5.12).
A further example for plant P450s capable of multiple subsequent oxidations
is represented by CYP71AV1 from Artemisia annua, which will be discussed in
Section 5.3.3.2.