1. Biochemistry and Chemical Biology
  2. Structural Biology and Molecular Biophysics

Structure of Fam20A reveals a pseudokinase featuring unique disulfide pattern and inverted ATP-binding

  1. Jixin Cui
  2. Qinyu Zhu
  3. Hui Zhang
  4. Michael A Cianfrocco
  5. Andres E Leschziner
  6. Jack E Dixon  Is a corresponding author
  7. Junyu Xiao  Is a corresponding author
  1. University of California, San Diego, United States
  2. Peking University, China
https://doi.org/10.7554/eLife.23990
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  1. Jixin Cui
  2. Qinyu Zhu
  3. Hui Zhang
  4. Michael A Cianfrocco
  5. Andres E Leschziner
  6. Jack E Dixon
  7. Junyu Xiao
(2017)
Structure of Fam20A reveals a pseudokinase featuring unique disulfide pattern and inverted ATP-binding
eLife 6:e23990.
https://doi.org/10.7554/eLife.23990
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Abstract

Mutations in FAM20A cause tooth enamel defects known as Amelogenesis Imperfecta (AI) and renal calcification. We previously showed that Fam20A is a secretory pathway pseudokinase and allosterically activates the physiological casein kinase Fam20C to phosphorylate secreted proteins important for biomineralization (Cui et al., 2015). Here we report the nucleotide-free and ATP-bound structures of Fam20A. Fam20A exhibits a distinct disulfide bond pattern mediated by a unique insertion region. Loss of this insertion due to abnormal mRNA splicing interferes with the structure and function of Fam20A, resulting in AI. Fam20A binds ATP in the absence of divalent cations, and strikingly, ATP is bound in an inverted orientation compared to other kinases. Fam20A forms a dimer in the crystal, and residues in the dimer interface are critical for Fam20C activation. Together, these results provide structural insights into the function of Fam20A and shed light on the mechanism by which Fam20A mutations cause disease.

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Author details

  1. Jixin Cui

    Department of Pharmacology, University of California, San Diego, La Jolla, United States
    Competing interests
    The authors declare that no competing interests exist.

  2. Qinyu Zhu

    Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
    Competing interests
    The authors declare that no competing interests exist.

  3. Hui Zhang

    Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
    Competing interests
    The authors declare that no competing interests exist.

  4. Michael A Cianfrocco

    Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, United States
    Competing interests
    The authors declare that no competing interests exist.

  5. Andres E Leschziner

    Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, United States
    Competing interests
    The authors declare that no competing interests exist.

  6. Jack E Dixon

    Department of Pharmacology, University of California, San Diego, La Jolla, United States
    For correspondence
    jedixon@ucsd.edu
    Competing interests
    The authors declare that no competing interests exist.

  7. Junyu Xiao

    The State Key Laboratory of Protein and Plant Gene Research, Peking University, Beijing, China
    For correspondence
    junyuxiao@pku.edu.cn
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-1822-1701

Funding

National Natural Science Foundation of China (31570735)

  • Junyu Xiao

National Key Research & Development Plan (2016YFC0906000)

  • Junyu Xiao

National Institutes of Health (DK018849)

  • Jack E Dixon

National Institutes of Health (DK018024)

  • Jack E Dixon

Human Frontier Science Program (LT000659/2013-L)

  • Jixin Cui

Damon Runyon Cancer Research Foundation (DRG 2171-13)

  • Michael A Cianfrocco

Howard Hughes Medical Institute

  • Jack E Dixon

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Tony Hunter, Salk Institute for Biological Studies, United States

Version history

  1. Received: December 8, 2016
  2. Accepted: April 20, 2017
  3. Accepted Manuscript published: April 22, 2017 (version 1)
  4. Version of Record published: May 2, 2017 (version 2)

Copyright

© 2017, Cui et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Jixin Cui
  2. Qinyu Zhu
  3. Hui Zhang
  4. Michael A Cianfrocco
  5. Andres E Leschziner
  6. Jack E Dixon
  7. Junyu Xiao
(2017)
Structure of Fam20A reveals a pseudokinase featuring unique disulfide pattern and inverted ATP-binding
eLife 6:e23990.
https://doi.org/10.7554/eLife.23990

Share this article

https://doi.org/10.7554/eLife.23990

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    Although numerous extracellular phosphoproteins have been identified, the protein kinases within the secretory pathway have only recently been discovered, and their regulation is virtually unexplored. Fam20C is the physiological Golgi casein kinase, which phosphorylates many secreted proteins and is critical for proper biomineralization. Fam20A, a Fam20C paralog, is essential for enamel formation, but the biochemical function of Fam20A is unknown. Here we show that Fam20A potentiates Fam20C kinase activity and promotes the phosphorylation of enamel matrix proteins in vitro and in cells. Mechanistically, Fam20A is a pseudokinase that forms a functional complex with Fam20C, and this complex enhances extracellular protein phosphorylation within the secretory pathway. Our findings shed light on the molecular mechanism by which Fam20C and Fam20A collaborate to control enamel formation, and provide the first insight into the regulation of secretory pathway phosphorylation.

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