Conformational selection dominates binding of steroids to human cytochrome P450 17A1.

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Guengerich FP, Wilkey CJ, Glass SM, Reddish MJ

Conformational selection dominates binding of steroids to human cytochrome P450 17A1.

J Biol Chem. 2019 Jun 28;294(26):10028-10041. doi: 10.1074/jbc.RA119.008860. Epub 2019 May 9.

PubMed ID

31072872 [ View in PubMed

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Abstract

Cytochrome P450 (P450, CYP) enzymes are the major catalysts involved in the oxidation of steroids as well as many other compounds. Their versatility has been explained in part by flexibility of the proteins and complexity of the binding mechanisms. However, whether these proteins bind their substrates via induced fit or conformational selection is not understood. P450 17A1 has a major role in steroidogenesis, catalyzing the two-step oxidations of progesterone and pregnenolone to androstenedione and dehydroepiandrosterone, respectively, via 17alpha-hydroxy (OH) intermediates. We examined the interaction of P450 17A1 with its steroid substrates by analyzing progress curves (UV-visible spectroscopy), revealing that the rates of binding of any of these substrates decreased with increasing substrate concentration, a hallmark of conformational selection. Further, when the concentration of 17alpha-OH pregnenolone was held constant and the P450 concentration increased, the binding rate increased, and such opposite patterns are also diagnostic of conformational selection. Kinetic simulation modeling was also more consistent with conformational selection than with an induced-fit mechanism. Cytochrome b 5 partially enhances P450 17A1 lyase activity by altering the P450 17A1 conformation but did not measurably alter the binding of 17alpha-OH pregnenolone or 17alpha-OH progesterone, as judged by the apparent Kd and binding kinetics. The P450 17A1 inhibitor abiraterone also bound to P450 17A1 in a multistep manner, and modeling indicated that the selective inhibition of the two P450 17A1 steps by the drug orteronel can be rationalized only by a multiple-conformation model. In conclusion, P450 17A1 binds its steroid substrates via conformational selection.

DrugBank Data that Cites this Article

Drug Enzymes

Drug	Enzyme	Kind	Organism	Pharmacological Action	Actions
Prasterone	Steroid 17-alpha-hydroxylase/17,20 lyase	Protein	Humans	Unknown	Product of	Details