Arabidopsis CYP72C1 is an atypical cytochrome P450 that inactivates brassinosteroids.
Cytochrome P450 monooxygenases (P450s) are a diverse family of proteins that have specialized roles in secondary metabolism and in normal cell development. Two P450s in particular, CYP734A1 and CYP72C1, have been identified as brassinosteroid-inactivating enzymes important for steroid-mediated signal transduction in Arabidopsis thaliana. Genetic analyses have demonstrated that these P450s modulate growth throughout plant development. While members of the CYP734A subfamily inactivate brassinosteroids through C-26 hydroxylation, the biochemical activity of CYP72C1 is unknown. Because CYP734A1 and CYP72C1 in Arabidopsis diverge more than brassinosteroid inactivating P450s in other plants, this study examines the structure and biochemistry of each enzyme. Three-dimensional models were generated to examine the substrate binding site structures and determine how they might affect the function of each P450. These models have indicated that the active site of CYP72C1 does not contain several conserved amino acids typically needed for substrate hydroxylation. Heterologous expression of these P450s followed by substrate binding analyses have indicated that CYP734A1 binds active brassinosteroids, brassinolide and castasterone, as well as their upstream precursors whereas CYP72C1 binds precursors more effectively. Seedling growth assays have demonstrated that the genetic state of CYP734A1, but not CYP72C1, affected responsiveness to high levels of exogenous brassinolide supporting our observations that CYP72C1 acts on brassinolide precursors. Although there may be some overlap in their physiological function, the distinct biochemical functions of these proteins in Arabidopsis has significant potential to fine-tune the levels of different brassinosteroid hormones throughout plant growth and development.
Thornton
Leeann E
LE
Department of Biology, The College of New Jersey, Ewing, 08628, USA. thornton@tcnj.edu
Rupasinghe
Sanjeewa G
SG
Peng
Hao
H
Schuler
Mary A
MA
Neff
Michael M
MM
D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D060406:Brassinosteroids; D020134:Catalytic Domain; D002777:Cholestanols / Q000037:antagonists & inhibitors*; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D017343:Genes, Plant; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D009154:Mutation; D054464:Peroxiredoxins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010937:Plant Growth Regulators / Q000037:antagonists & inhibitors*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013260:Steroids, Heterocyclic / Q000037:antagonists & inhibitors*; D040681:Structural Homology, Protein
D029681:Arabidopsis Proteins; D060406:Brassinosteroids; D002777:Cholestanols; D017931:DNA Primers; D010937:Plant Growth Regulators; D011994:Recombinant Proteins; D013260:Steroids, Heterocyclic; C083545:castasterone; D003577:Cytochrome P-450 Enzyme System; C500888:CYP72C1 protein, Arabidopsis; C108214:BAS1 protein, Arabidopsis; D054464:Peroxiredoxins; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; C023623:brassinolide