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Updated: May 15, 2026

Identification of the Source of Secreted Proteins in the Kidney by Brefeldin A Injection
Published on: November 10, 2021
Secreted protein kinases
Vincent S Tagliabracci1, Lorenzo A Pinna, Jack E Dixon
1Department of Pharmacology, University of California, San Diego, La Jolla, CA, USA.
Abstract:
Protein kinases constitute one of the largest gene families and control many aspects of cellular life. In retrospect, the first indication for their existence was reported 130 years ago when the secreted protein, casein, was shown to contain phosphate. Despite its identification as the first phosphoprotein, the responsible kinase has remained obscure. This conundrum was solved with the discovery of a novel family of atypical protein kinases that are secreted and appear to phosphorylate numerous extracellular proteins, including casein. Fam20C, the archetypical member, phosphorylates secreted proteins within Ser-x-Glu/pSer motifs. This discovery has solved a 130-year-old mystery and has shed light on several human disorders of biomineralization.
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