Cell Biology

The Real McCoy

Science Signaling  05 Jun 2012:
Vol. 5, Issue 227, pp. ec155
DOI: 10.1126/scisignal.2003275

Some secreted proteins are phosphorylated, the most prominent example being the milk protein casein, but the enzymes that catalyze such phosphorylation have not been identified. (The proteins known as “casein kinases” are in fact cytosolic proteins and do not mediate physiological phosphorylation of casein.) Tagliabracci et al. searched for a human protein with the characteristics expected of a secretory protein kinase and identified Fam20C. Mutations in the gene encoding Fam20C cause defects in bone formation. Furthermore, the consensus sequence for Fam20C phosphorylation was found in several secreted proteins that function in biomineralization. Thus, Fam20C appears to be the “real” casein kinase and to function in bone physiology.

V. S. Tagliabracci, J. L. Engel, J. Wen, S. E. Wiley, C. A. Worby, L. N. Kinch, J. Xiao, N. V. Grishin, J. E. Dixon, Secreted kinase phosphorylates extracellular proteins that regulate biomineralization. Science 336, 1150–1153 (2012). [Abstract] [Full Text]