Fig. 2.

The Z-disc is the main site of protein phosphorylation in sarcomeres. A, Numbers of (phospho-)proteins and phosphosites (p-sites) identified in contracting C2C12 myotubes. Localized p-sites were identified with a MaxQuant localization probability score ≥ 0.75. B, Distribution of p-sites according to the number of sites per protein. C, D, Distribution of p-sites identified in sarcomeric proteins of the I- or A-band (C). 532 p-sites (91%) were identified in proteins of the I-band. Of these, 412 p-sites (77%) were identified in true Z-disc and Z-disc-associated proteins, which is an essential structural part of the I-band (D). E, Classification of p-sites localized in 44 Z-disc-associated proteins. 264 p-sites (83%) were identified with high confidence with a MaxQuant localization probability ≥ 0.90 (red). Further 53 p-sites were localized with a probability ≥ 0.75 and < 0.90 (gray). F, G, GO-term enrichment analysis of the C2C12 myotube proteome (F) and phosphoproteome (G) data set established in this work. p values after Benjamini-Hochberg false discovery rate (FDR < 0.05) correction were plotted against their corresponding GO-terms from the three main domains “cellular component” (CC), “molecular function” (MF) and “biological process” (BP). Numbers of identified proteins for each term are shown in brackets.