7t8q
CRYSTAL STRUCTURE OF T151G CAO1
Structural highlights
FunctionCAO1_NEUCR Dioxygenase that cleaves the interphenyl C-alpha-C-beta double bond of resveratrol to yield 3,5-dihydroxybenzaldehyde and 4-hydroxybenzaldehyde (PubMed:23893079, PubMed:28493664). Cleaves also piceatannol, a compound that differs from resveratrol only in the occurrence of an additional hydroxyl group, which leads to the production of 3,4-dihydroxybenzaldehyde and 3,5-hydroxybenzaldehyde (PubMed:23893079, PubMed:28493664). Is not able to cleave trans-stilbene, 4-monohydroxy-trans-stilbene, 3,5-dihydroxy-trans-stilbene (pinosylvin), trismethoxy-resveratrol, and 3,3',5-trihydroxy-4'-methoxystilbene-3-O-beta-D-glucoside (PubMed:23893079). Is not involved in carotenoid metabolism (PubMed:23893079).[1] [2] Publication Abstract from PubMedCarotenoid cleavage dioxygenases (CCDs) are non-heme Fe(II) enzymes that catalyze the oxidative cleavage of alkene bonds in carotenoids, stilbenoids, and related compounds. How these enzymes control the reaction of O(2) with their alkene substrates is unclear. Here, we apply spectroscopy in conjunction with X-ray crystallography to define the iron coordination geometry of a model CCD, CAO1, in its resting state and following substrate binding and coordination sphere substitutions. Resting CAO1 exhibits a five-coordinate (5C), square pyramidal Fe(II) center that undergoes steric distortion towards a trigonal bipyramidal geometry in the presence of piceatannol. Titrations with the O(2)-analog, nitric oxide (NO), show a >100-fold increase in iron-NO affinity upon substrate binding, defining a crucial role for the substrate in activating the Fe(II) site for O(2) reactivity. The importance of the 5C Fe(II) structure for reactivity was probed through mutagenesis of the second-sphere Thr151 residue of CAO1, which occludes ligand binding at the sixth coordination position. A T151G substitution resulted in the conversion of the iron center to a six-coordinate (6C) state and a 135-fold reduction in apparent catalytic efficiency towards piceatannol compared to the wild-type enzyme. Substrate complexation resulted in partial 6C to 5C conversion, indicating solvent dissociation from the iron center. Additional substitutions at this site demonstrated a general functional importance of the occluding residue within the CCD superfamily. Taken together, these data suggest an ordered mechanism of CCD catalysis occurring via substrate-promoted solvent replacement by O(2). CCDs thus represent a new class of mononuclear non-heme Fe(II) enzymes. Spectroscopy and crystallography define carotenoid oxygenases as a new subclass of mononuclear non-heme Fe(II) enzymes.,DeWeese DE, Everett MP, Babicz JT Jr, Daruwalla A, Solomon EI, Kiser PD J Biol Chem. 2025 Mar 25:108444. doi: 10.1016/j.jbc.2025.108444. PMID:40147775[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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