Figure 5: Tissue distribution and amino-acid sequence features of localized phosphorylation sites.

(a) Histograms depicting the percentages of serine, threonine and tyrosine phosphorylation sites identified in each rat tissue as well as in human skeletal muscle samples. The total number of S, T and Y phosphorylation sites across all tissues and their relative abundance in percent is stated above each histogram. (b) Heat map visualizing relative abundance of sequence motifs matching the indicated kinases from phosphopeptides identified in all tissues investigated. (c) Top: amino-acid sequence patterns for all S and T phosphorylation sites in brain and testis. Bottom: amino-acid sequence patterns for tissue-specific versus non-specific S and T phosphorylation sites for brain and testis. (d) Hierarchical cluster of pathway analysis of phosphotyrosine-containing proteins. (e) Protein–protein interaction network build from tyrosine-phosphorylated proteins identified in human skeletal muscle using InWeb shows that these proteins significantly interact with each other (Adj. P=2e-4, using a permuation test). The resulting network shows that tyrosine-phosphorylated proteins collaborate in muscle contraction, oxygen transport and cell proliferation to carry out physiological processes relevant to the tissue in question. The input proteins from human skeletal muscle are depicted as yellow spheres, whereas interacting proteins reported in the literature are depicted as grey spheres.