Fig. 6. Two-dimensional phosphopeptide maps of tau constructs expressed in Sf9 cells and phosphorylated by endogenous kinases. Biernat J , and Mandelkow E Mol. Biol. Cell 1999;10:727-740 Copyright © 1999 The American Society for Cell Biology Two-dimensional phosphopeptide maps of tau constructs expressed in Sf9 cells and phosphorylated by endogenous kinases. (A) htau23 (higher magnification); (B) htau23/AP; (C) KXGA/R1/3/4; (D) construct K19 phosphorylated with PKA; (E) mixture of tau23 and K19 phosphorylated with PKA. In A the majority of spots are generated by phosphopeptides containing one or more of the 14 SP and TP motifs. The four phosphorylation sites in the repeats are highlighted and underlined (three KXGS motifs with S262, S324, and S356, plus S320). In B all SP or TP motifs are changed into AP so that the remaining major phosphorylation sites are Ser214 and those in the repeats, plus some unknown spots. In C the KXGS motifs in the repeats are changed into KXGA and are therefore absent from the map; besides the phosphorylated SP and SP motifs one observes S214 and S320. In D the repeat construct K19 was phosphorylated with PKA, showing only the sites S262, S324, S356, and S320. This sample was run together with tau23 in E to identify the sites. For details on analysis of phosphopeptides, see Illenberger et al. (1998).