Mass Spec Analysis of PTMs Using Minimal Sample Material

DNA is organized by protein:DNA complexes called nucleosomes in eukaryotes. Nucleosomes are composed of 147 base pairs of DNA wrapped around a histone octamer containing two copies of each core histone protein. Histone proteins play significant roles in many nuclear processes including transcription, DNA damage repair and heterochromatin formation. Histone proteins are extensively and dynamically post-translationally modified, and these post-translational modifications (PTMs) are thought to comprise a specific combinatorial PTM profile of a histone that dictates its specific function.  Abnormal regulations of PTM may lead to developmental disorders and disease development such as cancer.

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Cell free application: Sumoylation characterization

Small Ubiquitin-like Modifier (or SUMO) proteins are a family of small proteins that are covalently attached to and detached from other proteins in cells to modify their function. SUMOylation is a post-translational modification involved in various cellular processes, such as nuclear-cytosolic transport,
transcriptional regulation, apoptosis, protein stability and response to stress.

In contrast to ubiquitin, SUMO is not used to tag proteins for degradation. Mature SUMO is produced when the last four amino acids of the C-terminus have been cleaved off to allow formation of an isopeptide bond between the C-terminal glycine residue of SUMO and an acceptor lysine on the target protein.

Cell free expression can be used to characterize sumoylation of proteins. Target proteins are expressed in a rabbit reticulocyte cell free system (supplemented with necessary addition components,). Proteins that have been modified can be analyzed by a shift in migration on polyacrylamide gels, when compared to control reactions.

The following references illustrate the use of cell free expression for this application.

Brandl, A. et al. (2012) Dynamically regulated sumoylation of HDAC2 controls p53 deacetylation and restricts apoptosis following genotoxic stress. J. Mol. Cell. Biol. (online only)

Janer, A. et al. (2010). SUMOylation attenuates the aggregation propensity and cellular toxicity of the polyglutamine expanded ataxin-7. Human. Mol. Gen. 19, 181—95.

Rytinki, M. et al. (2009) SUMOylation attenuates the function of PGC-1alpha. J. Biol. Chem. 284, 26184-93.

Klein, U. et al. (2009) RanBP2 and SENP3 function in a mitotic SUMO2/3 conjugation-deconjugation cycle on Borealin. Mol. Cell. Biol. 20, 410–18.

Seo, W. and Ziltener, H. (2009) CD43 processing and nuclear translocation of CD43 cytoplasmic tail are required for cell homeostasis. Blood, 114, 3567–77.