CREBtide, a synthetic 13 amino acid peptide, has been reported as a PKA substrate.
delta-CREB is a spliced variant of cAMP response element binding protein (CREB). CREBtide (KRREILSRRPSYR), a synthetic peptide based on the phosphorylation sequence in delta-CREB. delta-CREB and CREBtide are tested as substrates of cAMP-dependent protein kinase (cAK). The apparent Km of CREBtide phosphorylation by cAK is 3.9 μM, which is 10-fold lower than that of Kemptide (Km=39 μM), the synthetic peptide substrate most often employed for cAK measurement. The Vmax values are 12.4 mumol/(min.mg) for CREBtide and 9.8 mumol/(min.mg) for Kemptide. The apparent Km of CREBtide phosphorylation by cGMP-dependent protein kinase (cGK) is 2.9 μM and the Vmax value is 3.2 mumol/(min.mg). Both delta-CREB and CREBtide are phosphorylated at a much slower rate by cGK as compared with cAK, implying that the high cAK/cGK specificity exhibits by delta-CREB is retained by the peptide[2].
[1]. Wu J, et al. A microPLC-based approach for determining kinase-substrate specificity. Assay Drug Dev Technol. 2007 Aug;5(4):559-66. [2]. Colbran JL, et al. cAMP-dependent protein kinase, but not the cGMP-dependent enzyme, rapidly phosphorylates delta-CREB, and a synthetic delta-CREB peptide. Biochem Cell Biol. 1992 Oct-Nov;70(10-11):1277-82.