O R G A N I I C C H E M I I S T R Y S E M I I N A R
Our genomic DNA is stored in the nuclei of our cells in the form of a nucleoprotein complex called chromatin. Histones are the major protein component of chromatin and their post-translational modifications (PTMs) dictate the structure and function of chromatin. Histone PTMs range in size from a small methyl group to entire proteins such as ubiquitin and the small ubiquitin-like modifier protein,
SUMO. The untimely installation or removal of histone PTMs by environmental and genetic cues underlies acute diseases such as leukemias and glioblastomas. Elucidating the mechanisms by which histone PTMs control gene function during normal cellular development is an essential first step toward understanding how their misregulation leads to human diseases.
Modification of the histone H4 N-terminal tail region by SUMO is associated with gene repression in human cell lines. However, the mechanism by which SUMO acts in silencing is entirely unknown.
This is because understanding SUMO-specific effects on chromatin structure and function requires the ability to study these in the absence of other chromatin PTMs. However, the heterogeneity of histone
PTMs and the small amounts of SUMOylated H4 in our cells make such studies extremely challenging.
We have overcome this problem by applying a disulfide-directed strategy to chemically synthesize uniformly SUMOylated histone H4 (suH4) in multi-milligram quantities. Synthetic suH4 was successfully incorporated into chromatin arrays and subjected to biophysical characterization at physiological magnesium concentrations. A combination of ensemble averaged and single-molecule measurements revealed that suH4 prevents chromatin compaction by inhibiting long-range interactions between nucleosomes. Thus, our results suggest that SUMO may mediate gene repression without formation of the compact structures that are typically associated with silenced genes.
Thursday, October 22, 2015 - 11:00 AM
Chemistry #1315