Post-translational modifications location

Field Proteomics, noncovalent interaction, structural determination, PTM. Technique Electrospray for sequencing, post-translational modification location, and noncovalent interactions. 

The Location of Post-Translational Modifications Using LC-MS Data from an Enzyme Digest 170... 

Post-translational modification may affect the biological activity of a protein and the location of such modifications is an extension of sequencing. 

As described in more detail below, agonist binding will lead to signaling as well as phosphorylation of Ser and Thr residues, especially, but also, in selected cases, Tyr residues located in intracellular loop-3 and in the C-terminal extension. This post-translational modification alters the affinity of the receptor for various intracellular proteins, including arrestin, which sterically prevents further G-protein binding and functions as an adaptor protein. Also, interaction with other types of scaffolding proteins such as PSD-95-like proteins, is influenced by the phosphorylation state of the receptor. 

The formation of an aldehyde group on a macromolecule can produce an extremely useful derivative for subsequent modification or conjugation reactions. In their native state, proteins, peptides, nucleic acids, and oligonucleotides contain no naturally occurring aldehyde residues. There are no aldehydes on amino acid side chains, none introduced by post-translational modifications, and no formyl groups on any of the bases or sugars of DNA and RNA. To create reactive aldehydes at specific locations within these molecules opens the possibility of directing modification reactions toward discrete sites within the macromolecule. 

Within the nucleosome, addition of ubiquitin to H2A occurs near the entry and exit sites of DNA and the binding site of HI [203]. Therefore, this post-translational modification is expected to have implications for both the stability of the particle and higher order structure of chromatin [45,203]. The C-terminal end of H2B and its ubiquitination site on the other hand is located at the opposite side of the nucleosome [45]. Incorporation of an ubiquitin adduct into the nucleosome at this site may have significant implications for the trajectory of the DNA and the integrity of the particle. In this regard there have been multiple biochemical results substantiating a role of H2B ubiquitination in transcriptional activation [207-210]. 

A true appreciation of the subtle and complex ways in which the nucleosome can influence gene expression, has come only recently, largely through studies of the post-translational modifications to which all histones are subject and of the enzymes that add and remove these modifications. It has been known for many years that the histone N-terminal tails are exposed on the surface of the nucleosome and that selected amino acid residues are subject to a variety of enzyme-catalyzed, post-translational modifications. These include acetylation of lysines, phosphorylation of serines, and methylation of lysines and arginines ([6,7], see also chapters by Davie, and Ausio and Abbott, this volume). The locations of the histone N-terminal tails in the nucleosome and the residues that can be modified are shown in Fig. 1. 

---