17α-Hydroxylase/17,20-Lyase Deficiency as a Model to Study Enzymatic Activity Regulation: Role of Phosphorylation*

Abstract

Cytochrome P450 17alpha-hydroxylase (CYP17) is a single gene-encoded protein with two activities: 17alpha-hydroxylase and 17,20-lyase. The two catalytic activities are differentially regulated in health and disease. We took advantage of naturally occurring human mutations to understand the molecular bases of this differential regulation. We identified eight novel mutations in the CYP17 gene, different in nature and spread throughout the gene. As posttranslational modifications appear to be important for activity control, we investigated the phosphorylation state of wild-type and mutant CYP17 proteins. Although phospholabeled protein was seen when the wild-type and most mutant proteins were expressed, no phosphorylation was detected for the F417C mutant. F417C is the only 17,20-lyase deficiency case confirmed at the molecular level and represents the first phosphorylation CYP17-deficient mutant. In search of the physiological agents involved in this process, the effect of cAMP was tested on activity and phosphorylation state of our mutant CYP17 proteins. cAMP stimulates activity and phosphorylation in all cases, except in the F417C and R35L mutants. The lack of response to the physiological second messenger might explain the different phenotypes. The F417C mutant protein, which is already shown to be associated with the lack of electron transfer, provides for the first time a link between the electron transfer system and the phosphorylation state of the CYP17 enzyme in the control of 17,20-lyase activity.

A compound heterozygous mutation in the CYP17 (17α-hydroxylase/17,20-lyase) gene in a Chinese subject with congenital adrenal hyperplasia

“…On the other hand, some patients, particularly those of Japanese origin [2,8], may present as hyperaldosteronism. In other expression studies, it was determined in all complete deficiency cases that both activities were diminished to the same extent and confirmed that the CYP17 enzyme must retain about one fourth of its catalytic capability to prevent the onset of mineralocorticoid-dependent hypertension [16].…”

Molecular Modeling on Inhibitor Complexes and Active-Site Dynamics of Cytochrome P450 C17, a Target for Prostate Cancer Therapy

“…The point mutations R96W and R96Q completely abolish both lyase and hydroxylase activities of the enzyme. 20,21 The present model suggests that the hydrogen bonding between R96 and the propionate chains helps to hold the heme in its position. Loss of this hydrogenbond pattern by mutation of this residue would lead to mispositioning of the heme and loss of enzymatic activity.…”

Nonhuman primates as models for human adrenal androgen production: Function and dysfunction

“…While it has been suggested phosphorylation affects binding of substrate and so changes the rate of reaction (Lohr et al 1997) it has also been proposed that phosphorylation facilitates the interaction of CYP17 with other proteins such as CYB5 (Miller et al 1997, Biason Lauber 2000a, Gupta et al 2001). A multiplicity of putative regulatory mechanisms could certainly exist and this would indeed explain how local markers such as high CYB5 and low HSD3B2 can indicate histologically a tissue’s potential ability to generate DHEA via the delta five pathway, yet other factors may also determine if the cells actually do make C19 steroids, or at least how much steroid.…”