TY - JOUR
T1 - Compound i is the reactive intermediate in the first monooxygenation step during conversion of cholesterol to pregnenolone by cytochrome P450scc
T2 - EPR/ENDOR/cryoreduction/annealing studies
AU - Davydov, Roman
AU - Gilep, Andrey A.
AU - Strushkevich, Natallia V.
AU - Usanov, Sergey A.
AU - Hoffman, Brian M.
PY - 2012/10/17
Y1 - 2012/10/17
N2 - Cytochrome P450scc (CYP11A1) catalyzes conversion of cholesterol (CH) to pregnenolone, the precursor to all steroid hormones. This process proceeds via three sequential monooxygenation reactions: two stereospecific hydroxylations with formation first of 22R-hydroxycholesterol (22-HC) and then 20±,22R-dihydroxycholesterol (20,22-DHC), followed by C20-C22 bond cleavage. Herein we have employed EPR and ENDOR spectroscopy to characterize the intermediates in the first hydroxylation step by 77 K radiolytic one-electron cryoreduction and subsequent annealing of the ternary oxy-cytochrome P450scc-cholesterol complex. This approach is fully validated by the demonstration that the cryoreduced ternary complex of oxy-P450scc-CH is catalytically competent and hydroxylates cholesterol to form 22-HC with no detectable formation of 20-HC, just as occurs under physiological conditions. Cryoreduction of the ternary complex trapped at 77 K produces predominantly the hydroperoxy-ferriheme P450scc intermediate, along with a minor fraction of peroxo-ferriheme intermediate that converts into a new hydroperoxo-ferriheme species at 145 K. This behavior reveals that the distal pocket of the parent oxy-P450scc-cholesterol complex exhibits an efficient proton delivery network, with an ordered water molecule H-bonded to the distal oxygen of the dioxygen ligand. During annealing of the hydroperoxy-ferric P450scc intermediates at 185 K, they convert to the primary product complex in which CH has been converted to 22-HC. In this process, the hydroperoxy-ferric intermediate decays with a large solvent kinetic isotope effect, as expected when proton delivery to the terminal O leads to formation of Compound I (Cpd I). 1H ENDOR measurements of the primary product formed in deuterated solvent show that the heme Fe(III) is coordinated to the 22R-O1H of 22-HC, where the 1H is derived from substrate and exchanges to D after annealing at higher temperatures. These observations establish that Cpd I is the agent that hydroxylates CH, rather than the hydroperoxy-ferric heme.
AB - Cytochrome P450scc (CYP11A1) catalyzes conversion of cholesterol (CH) to pregnenolone, the precursor to all steroid hormones. This process proceeds via three sequential monooxygenation reactions: two stereospecific hydroxylations with formation first of 22R-hydroxycholesterol (22-HC) and then 20±,22R-dihydroxycholesterol (20,22-DHC), followed by C20-C22 bond cleavage. Herein we have employed EPR and ENDOR spectroscopy to characterize the intermediates in the first hydroxylation step by 77 K radiolytic one-electron cryoreduction and subsequent annealing of the ternary oxy-cytochrome P450scc-cholesterol complex. This approach is fully validated by the demonstration that the cryoreduced ternary complex of oxy-P450scc-CH is catalytically competent and hydroxylates cholesterol to form 22-HC with no detectable formation of 20-HC, just as occurs under physiological conditions. Cryoreduction of the ternary complex trapped at 77 K produces predominantly the hydroperoxy-ferriheme P450scc intermediate, along with a minor fraction of peroxo-ferriheme intermediate that converts into a new hydroperoxo-ferriheme species at 145 K. This behavior reveals that the distal pocket of the parent oxy-P450scc-cholesterol complex exhibits an efficient proton delivery network, with an ordered water molecule H-bonded to the distal oxygen of the dioxygen ligand. During annealing of the hydroperoxy-ferric P450scc intermediates at 185 K, they convert to the primary product complex in which CH has been converted to 22-HC. In this process, the hydroperoxy-ferric intermediate decays with a large solvent kinetic isotope effect, as expected when proton delivery to the terminal O leads to formation of Compound I (Cpd I). 1H ENDOR measurements of the primary product formed in deuterated solvent show that the heme Fe(III) is coordinated to the 22R-O1H of 22-HC, where the 1H is derived from substrate and exchanges to D after annealing at higher temperatures. These observations establish that Cpd I is the agent that hydroxylates CH, rather than the hydroperoxy-ferric heme.
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U2 - 10.1021/ja3067226
DO - 10.1021/ja3067226
M3 - Article
C2 - 23039857
AN - SCOPUS:84867515001
VL - 134
SP - 17149
EP - 17156
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 41
ER -