Spatially restricted substrate-binding site of cortisol-synthesizing CYP11B1 limits multiple hydroxylations and hinders aldosterone synthesis

Kuniaki Mukai, Hiroshi Sugimoto, Katsumasa Kamiya, Reiko Suzuki, Tomomi Matsuura, Takako Hishiki, Hideo Shimada, Yoshitsugu Shiro, Makoto Suematsu, Norio Kagawa

Research output: Contribution to journalArticlepeer-review

Abstract

Human cytochromes P45011β (CYP11B1) and P450aldo (CYP11B2) are monooxygenases that synthesize cortisol through steroid 11β-hydroxylation and aldosterone through a three-step process comprising 11β-hydroxylation and two 18-hydroxylations, respectively. CYP11B1 also catalyzes 18-monohydroxylation and 11β,18-dihydroxylation. To study the molecular basis of such catalytic divergence of the two enzymes, we examined a CYP11B1 mutant (Mt-CYP11B1) with amino acid replacements on the distal surface by determining the catalytic activities and crystal structure in the metyrapone-bound form at 1.4-Å resolution. Mt-CY11B1 retained both 11β-hydroxylase and 18-hydroxylase activities of the wild type (Wt-CYP11B1) but lacked 11β,18-dihydroxylase activity. Comparisons of the crystal structure of Mt-CYP11B1 to those of Wt-CYP11B1 and CYP11B2 that were already reported show that the mutation reduced the innermost space putatively surrounding the C3 side of substrate 11-deoxycorticosterone (DOC) bound to Wt-CYP11B1, while the corresponding space in CYP11B2 is enlarged markedly and accessible to bulk water through a channel. Molecular dynamics simulations of their DOC-bound forms supported the above findings and revealed that the enlarged space of CYP11B2 had a hydrogen bonding network involving water molecules that position DOC. Thus, upon positioning 11β-hydroxysteroid for 18-hydroxylation in their substrate-binding sites, steric hindrance could occur more strongly in Mt-CYP11B1 than in Wt-CYP11B1 but less in CYP11B2. Our investigation employing Mt-CYP11B1 sheds light on the divergence in structure and function between CYP11B1 and CYP11B2 and suggests that CYP11B1 with spatially-restricted substrate-binding site serves as 11β-hydroxylase, while CYP11B2 with spatially-extended substrate-binding site successively processes additional 18-hydroxylations to produce aldosterone.

Original languageEnglish
Pages (from-to)192-205
Number of pages14
JournalCurrent Research in Structural Biology
Volume3
DOIs
Publication statusPublished - 2021 Jan

Keywords

  • Adrenal
  • Cytochrome P450
  • Molecular dynamics
  • Steroid hormone
  • X-ray crystallography

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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