Letter | Published:

Structure of an integral membrane sterol reductase from Methylomicrobium alcaliphilum

Nature volume 517, pages 104107 (01 January 2015) | Download Citation

Abstract

Sterols are essential biological molecules in the majority of life forms. Sterol reductases1 including Δ14-sterol reductase (C14SR, also known as TM7SF2), 7-dehydrocholesterol reductase (DHCR7) and 24-dehydrocholesterol reductase (DHCR24) reduce specific carbon–carbon double bonds of the sterol moiety using a reducing cofactor during sterol biosynthesis. Lamin B receptor2 (LBR), an integral inner nuclear membrane protein, also contains a functional C14SR domain. Here we report the crystal structure of a Δ14-sterol reductase (MaSR1) from the methanotrophic bacterium Methylomicrobium alcaliphilum 20Z (a homologue of human C14SR, LBR and DHCR7) with the cofactor NADPH. The enzyme contains ten transmembrane segments (TM1–10). Its catalytic domain comprises the carboxy-terminal half (containing TM6–10) and envelops two interconnected pockets, one of which faces the cytoplasm and houses NADPH, while the other one is accessible from the lipid bilayer. Comparison with a soluble steroid 5β-reductase structure3 suggests that the reducing end of NADPH meets the sterol substrate at the juncture of the two pockets. A sterol reductase activity assay proves that MaSR1 can reduce the double bond of a cholesterol biosynthetic intermediate, demonstrating functional conservation to human C14SR. Therefore, our structure as a prototype of integral membrane sterol reductases provides molecular insight into mutations in DHCR7 and LBR for inborn human diseases.

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Accessions

Primary accessions

Protein Data Bank

Data deposits

Coordinates and structure factors for MaSR1 are deposited in the Protein Data Bank under accession code 4QUV.

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Acknowledgements

We thank W. Shi and H. Robinson at National Synchrotron Light Source (NSLS) beamline X29 and N. Sukumar at Advanced Photon Source (APS) beamline 24-ID-E for on-site assistance and J. Wang for support with the structure determination. We also thank L. Gatticchi and B. Sebastiani for assistance with the sterol reductase assays, and E. Coutavas, E. Debler and H. Shi for constructive comments in manuscript preparation. The C27Δ8,14 substrate was a gift to R.R. by G. Galli, University of Milano, Italy. This work was supported by funds from the Rockefeller University and the Howard Hughes Medical Institute. X.L. is supported by C.H. Li Memorial Scholar Fund fellowship of the Rockefeller University.

Author information

Affiliations

  1. Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York, New York 10065, USA

    • Xiaochun Li
    •  & Günter Blobel
  2. Department of Experimental Medicine, University of Perugia, Perugia 06132, Italy

    • Rita Roberti

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Contributions

X.L. designed the research and performed structural biological studies; X.L. and R.R. performed sterol reductase activity assays; X.L., R.R. and G.B. contributed to data analysis and manuscript preparation; X.L. and G.B. wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Xiaochun Li or Günter Blobel.

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https://doi.org/10.1038/nature13797

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