1 Structure of Fam20A reveals a pseudokinase featuring unique 2 disulfide pattern and inverted ATP-binding 3 4 Jixin Cui#,1, Qinyu Zhu#,2,3, Hui Zhang2,3, Michael A. Cianfrocco4, Andres E. 5 Leschziner4, Jack E. Dixon*1,4,5, Junyu Xiao*,3 6 7 1. Department of Pharmacology, University of California, San Diego, La Jolla, CA 8 92093, USA 9 2. Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 10 100871, China 11 3. The State Key Laboratory of Protein and Plant Gene Research, School of Life 12 Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, 13 100871, China 14 4. Department of Cellular and Molecular Medicine, University of California, San 15 Diego, San Diego, CA 92093, USA 16 5. Department of Chemistry and Biochemistry, University of California San Diego, 17 La Jolla, CA 92093, USA 18 19 # These authors contributed equally to this work 20 *Correspondence and requests for materials should be addressed to J.E.D 21 (
[email protected]) and J.X. (
[email protected]) 1 22 Abstract 23 Mutations in FAM20A cause tooth enamel defects known as Amelogenesis 24 Imperfecta (AI) and renal calcification. We previously showed that Fam20A is a 25 secretory pathway pseudokinase and allosterically activates the physiological casein 26 kinase Fam20C to phosphorylate secreted proteins important for biomineralization 27 (Cui et al., 2015). Here we report the nucleotide-free and ATP-bound structures of 28 Fam20A. Fam20A exhibits a distinct disulfide bond pattern mediated by a unique 29 insertion region. Loss of this insertion due to abnormal mRNA splicing interferes 30 with the structure and function of Fam20A, resulting in AI.