LITAF may sequester Itch to limit the ability of Itch to target proteins for degradation or to protect the cell from the putative harmful effects of Itch through its degradation. Interestingly, ubiquitination of Jun by Itch has been shown to trigger Jun accumulation to the lysosomal compartment, by a still unknown mechanism. The LITAF and Itch interaction could thus be a targeting mechanism to bring Itch substrates to the lysosome. Binding of small PPXY motif-containing proteins to Itch may also impact its activity. Ndfip1 and Ndfip2 binding have been shown to stimulate the ubiquitin ligase activity of both Itch and Nedd4. Conversely, N4BP1 strongly inhibits Itch-catalyzed polyubiquitination of several proteins by preventing the interaction between the ligase and its substrates, thereby reducing the transfer of ubiquitin molecules to Itch protein targets. On the other hand, due to the fact that Itch is an E3 ubiquitin ligase, the possibility exists that Itch re-localizes to or remains in late endosomes where it interacts with LITAF and mediates the transfer of ubiquitin to LITAF for future degradation. LITAF may represent another substrate of Itch and Itch may function to regulate cellular levels of LITAF by targeting it for degradation in the lysosome. Further studies will be important to elucidate the consequences of the novel interaction between LITAF and Itch. As proteins and their modifications are directly involved in nearly all biological processes, the identification and quantification of as many proteins and their post-translational modifications as possible from the same sample are the prerequisites for biological discovery. As peptides are more compatible with liquid chromatography separation and mass spectrometry detection, protein extracts are usually digested with a protease to yield a complex mixture of peptides in shotgun proteomics. To thoroughly ALK5 Inhibitor II characterize the proteome, multidimensional protein identification technology is commonly employed in which multidimensional liquid chromatography is used to reduce sample complexity and increase dynamic range of protein identification, and separate experiments with different types of enrichment methods are used for concentration of peptides of low abundance with PTMs for mass spectrometric characterization. In recent years, considerable attention has been paid to the study of information-rich subsets of the proteome, such as the phosphoproteome and glycoproteome, in order to improve the dynamic range of identified proteins. It has been estimated that about 50% of all proteins are SCH727965 clinical trial glycosylated and over one third of all proteins are phosphorylated in mammals. Phosphorylation is a dynamic and reversible modification involved in the regulation of many biological processes including metabolism, cell division, signal transduction and enzymatic activity.