Cytochrome P450
Monooxygenases
William Green
2/17/11
Background
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P450s are a group of heme-containing enzymes that utilize NADPH and/or NADH
to produce functionalized organic substrates
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All P450s contain a highly conserved motif found near the C terminus: F- -G-R-C-G
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Cytochrome P450-dependent monooxygenases “mediate a wide range of oxidative
reactions involved in the biosynthesis of plant secondary metabolites including
phenylpropanoids and phytoalexins” (Frank 1996).
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Superfamily containing more than 450 CYP sequences among at least 65 gene
families
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P450 proteins are anchored to the ER membrane by “a hydrophobic helix near the
N-terminus with most of the protein residing on the cytosolic face of the
membrane" (Chapple 1998).
Background Cont.
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Two groups of P450s:
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“Group A”: thought to have evolved since the divergence of plants from common ancestor
“Non-group A”: mostly closer to animal and fungal enzymes than group A proteins
Nomenclature:
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Relationships between P450s determined by amino acid sequence identity
Genes >40% identical are said to be in the same P450 family (ex. CYP71 or CYP73)
If 40% or less, the new sequence defines a new family
• Plant P450 genes begin with CYP71 through CYP99
• However recently these identifications have been exhaused and have seen been added to
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If in the same family, but share < 55% identity they are said to be in either of two subfamilies (ex.
CYP74A or CYP74B)
• If > 55% they are in the same subfamily (ex. CYP71C includes CYP71C1 - 5)
• Genes encoding proteins from different species are often members of the same subfamily
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If > or = 97% identity, they represent allelic variants of the same gene
Some Known P450s in Plants
Focus of Study
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First looked at highly conserved amino acids in heme binding domain
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Two main pathways of P450 monooxygenasese:
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Biosynthetic Pathway:
• Leads to syntheiss of: UV protectants (flavonoids), anthocyanins, isoflavonoids/phytoalexins,
fatty acids, hormones, signaling molecules, carotenoids, terpenes (defense compounds), and
lignins (structural compounds)
Detoxification Pathway:
• Drugs, carcinogens, herbicides and insecticides are all detoxified by P450 controlled
hydroxylations
Cinnamate-4-Hydroxylase (C4H) was the first P450 to be characterized
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C4H is encoded by the CYP73A subfamily
C4H catalyzes the para-hydroxylation of trans-cinnamic acid (derived from phenylalanine)
Known for involvment in phenylpropanoid pathway
Helps produce secondary metabolites: lignin, flavonoids, hydroxycinnamic acid esters, lignans,
stilbenes, etc.
Results
• Blasted P450 genes against Blueberry databases
– CYP73A1 mRNA from Helianthus tuberosus (Jerusalem artichoke)
– CYP73A3 mRNA from Medicago truncatula (Alfalfa)
– CYP73A5 mRNA from Arabidposis thaliana
– CYP73A9 mRNA from Pisum Sativum (pea)
– CYP82 mRNA from Vitis Vinifera (grape)
– C4H mRNA from Selaginella moellendorffii
Results Cont.
• 1 Hit found
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CYP73A9: evalue (4e-115)
Blasted sequence against 454 to obtain BB sequence
80% identity
Blasted against Illumina; 100% match with 454
0 hits in EST database
Implications & Direction
• Gene encoding C4H is in blueberry (possible
ortholog of CYP73A9)
• Want to examine heme binding domain
http://www.plantphysiol.org/cgi/content/abstract/110/3/1035
• Flavonoid-3’,5’-hydroxylase genes
Sources
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Chapple, Clint. "Molecular-Genetic Analysis Of Plant Cytochrome P450-Dependent
Monooxygenases." Annual Review of Plant Physiology and Plant Molecular Biology 49.1
(1998): 311-43. Annual Review. Web. 11 Feb. 2011. http://www.annualreviews.org/doi/
pdf/10.1146/annurev.arplant.49.1.311.
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Frank, Michael R., Joy M. Deyneka, and Mary A. Schuler. "Cloning of Wound-Induced
Cytocrome P450 Monooxygenases Expressed in Pea." Plant Physiology 110.3 (1996):
1035-046. PLANT PHYSIOLOGY®. American Society of Plant Biologists. Web. 09 Feb. 2011.
http://www.plantphysiol.org/cgi/content/abstract/110/3/1035.