Laboratory of Molecular and Cellular Neuroscience, Rockefeller University, New York, New York 10021-6399, USA.
The cytoplasmic domain of Alzheimer's beta-amyloid precursor protein (APP) can be phosphorylated at Thr654, Ser655, and Thr668 (APP695 isoform numbering). Previous studies demonstrated that Ser655 of APP was phosphorylated by protein kinase C (PKC) and calmodulin-dependent protein kinase II (CaMKII) in vitro and by unidentified protein kinase(s) in vivo. We report here the characterization of a novel protein kinase (designated APP kinase I) which phosphorylates Ser655 of APP. APP kinase I was partially purified over 7,000-fold from rat brain and identified as a approximately 43 kDa protein that is distinct from a number of known protein kinases, including PKC and extracellular signal-regulated kinases (ERKs). The identification of a novel protein kinase that phosphorylates Ser655 will hopefully contribute to our understanding of the metabolism and/or function of APP in the pathogenesis of Alzheimer's disease (AD). Copyright 1999 Academic Press.