Ubiquitin-Like Proteins Modify Chromatin to Modulate Gene Expression

Cell biologists have traced the molecular function of a protein that meditates an enzyme complex that chemically modifies chromatin and modulates gene expression.

The protein that was studied is called SUMO (small ubiquitin-related modifier). It is a member of 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, response to stress, and progression through the cell cycle. SUMO proteins are similar to ubiquitin, and an enzymatic cascade analogous to that involved in ubiquitination directs SUMOylation. In contrast to ubiquitin, SUMO is not used to tag proteins for degradation. While SUMO and ubiquitin have similar roles, they have little sequence similarity. On the other hand, they both contain the same structural "ubiquitin fold."

In the current study, investigators from Tufts University (Boston, MA, USA) worked with in vitro cell cultures. They reported in the April 24, 2009, online edition of the journal Molecular Cell that SUMO interacted with the LSD1/CoREST/HDAC enzyme complex to regulate genes by altering chromatin structure.

"We have only known for about 10 years that SUMO chemically modifies proteins. We have a good understanding of how SUMO modifies other proteins, but the actual mechanism of how this modification alters cell function is not well known. Our study uncovers a fundamental aspect of how SUMO works, which has implications for many diseases. Until now, SUMO and LSD1/CoREST/HDAC have not been studied together; we have found out how they work together to turn off certain genes," said senior author Dr. Grace Gill, associate professor of cellular biology at Tufts University.

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