Fig. 2

Biotinylation of cell surface proteins. A Bar chart showing the number of proteins identified with different numbers of biotinylated peptides. The y-axis represents the number of proteins identified by the number of biotinylated peptides shown on the x-axis. B Bubble plot representing the intensity of biotinylated peptides from the topmost abundant biotinylated proteins. The x-axis represents the number of biotinylated peptides identified per protein, and the y-axis represents the percent of biotinylation, as the proportion of known extracellular lysines in that protein that were detected with biotinylation. The diameter of each bubble is representative of the intensity of biotinylated peptides from that protein. C Pie chart showing the proportions of various proteins that were present in the resources referred to: SURFY (the in silico human surfaceome [3]), the Cancer Surfaceome Atlas [18], SURFME [19] and UniProt for annotations of secreted proteins [20]. D Relative proportions of the Gene Ontology annotations for molecular function of the identified biotinylated proteins