# The terminal steps of cortisol and aldosterone biosynthesis

> **NIH VA I01** · VETERANS HEALTH ADMINISTRATION · 2022 · —

## Abstract

Excess aldosterone and cortisol production from the human adrenal cortex commonly contributes to
hypertension, heart failure, obesity, glucose intolerance, and low bone mass. Cytochromes P450 11B2 and
P450 11B1 catalyze the final steps in the biosynthesis of aldosterone and cortisol, respectively. The zone-
specific regulation of these enzymes maintains salt and water balance or carbohydrate metabolism and
response to physiologic stress. The enzymes share 95% sequence similarity, and both catalyze the 11β-
hydroxylation of 11-deoxycorticosterone and 11-deoxycortisol. In contrast, the 18-hydroxylase of P450 11B1 is
poor compared to P450 11B2, and only P450 11B2 has 18-oxidase activity, which converts 18-hydroxy-
corticosterone to aldosterone. P450 11B2 has high processivity, in that the intermediates predominantly do not
dissociate before additional turnovers to aldosterone, but the reasons for this processivity and whether this
property is required for aldosterone production are not known. A comparison of its microscopic steps with
those of P450 11B1 offers an opportunity to understand the unique biochemistry of aldosterone production.
 Our long-term goal is to elucidate the biochemical and physical properties that confers high 18-
hydroxylase and moderate 18-oxidase activities to P450 11B2 but not P450 11B1. Our central hypotheses
are that: (1) the positioning of nascent corticosterone generated from 11-deoxycorticosterone in the active site
and the conformation of P450 11B2 is different that the nature of the complex when corticosterone binds as
initial substrate; and (2) that the processivity of P450 11B2 reflects a combination of slow dissociation rates
and high coupling efficiency with the intermediates. Consequently, the objectives of this application are to
characterize the binding constants, binding and dissociation rates, pre-steady state (single turnover) kinetics,
and coupling efficiencies for P450 11B1 and P450 11B2 with several substrates and to deduce which
parameters correlate best with processivity. As tools for these studies, we will employ mutations that alter the
activities for P450 11B1 and P450 11B2 and alternate substrates that have specific chemical properties.
 In Aim 1, we will dissect the 18-hydroxylase activity of P450 11B1 and P450 11B2, wild-type and
mutations. In Aim 2, we will focus on the 18-oxidase activity with a parallel series of studies as in Aim 2. In Aim
3, we will focus on extrinsic factors, specifically the lipid composition of the membrane environment, in
regulating the processivity and latter two activities of P450 11B2. We will use nanodiscs to generate artificial
enzyme-membrane systems and confirm key results in transfected HEK-293 or V79 cells. The work will utilize
the specialized instrumentation that the Auchus and Waskell laboratories have employed to study cytochrome
P450 enzymes for many years and state-of-the art tandem mass spectrometry at the University of Michigan. In
this manner, we will sy...

## Key facts

- **NIH application ID:** 10409567
- **Project number:** 5I01BX005084-02
- **Recipient organization:** VETERANS HEALTH ADMINISTRATION
- **Principal Investigator:** RICHARD J. AUCHUS
- **Activity code:** I01 (R01, R21, SBIR, etc.)
- **Funding institute:** VA
- **Fiscal year:** 2022
- **Award amount:** —
- **Award type:** 5
- **Project period:** 2021-07-01 → 2025-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10409567

## Citation

> US National Institutes of Health, RePORTER application 10409567, The terminal steps of cortisol and aldosterone biosynthesis (5I01BX005084-02). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10409567. Licensed CC0.

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