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

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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.

Data availability

The following data sets were generated

(2016) Crystal structure of Fam20A
Publicly available at the RCSB Protein Data Bank (accession no: 5WRR).

http://www.rcsb.org/pdb/explore/explore.do?structureId=5WRR
(2016) Crystal Structure of Fam20A in complex with ATP
Publicly available at the RCSB Protein Data Bank (accession no: 5WRS).

http://www.rcsb.org/pdb/explore/explore.do?structureId=5WRS

Article and author information

Author details

Jixin Cui

Department of Pharmacology, University of California, San Diego, La Jolla, United States

Competing interests
The authors declare that no competing interests exist.
Qinyu Zhu

Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China

Competing interests
The authors declare that no competing interests exist.
Hui Zhang

Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China

Competing interests
The authors declare that no competing interests exist.
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.
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.
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.
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.

"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.

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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.