Biology

Dr. Vignesh Kasinath
Helen Hay Whitney Postdoctoral Fellow Prof. Eva Nogales Lab, QB3 Institute University of California, Berkeley

Abstract:

The ability to establish and maintain stable cellular identity is critical for development in multicellular organisms. Central to this process is the chemical modification of histones and DNA caused by the regulated activity of chromatin modifying enzymes such as Polycomb. Polycomb repressive complex 2 (PRC2) is the only known methyltransferase enzyme specific for histone H3 lysine 27, and catalyzes its trimethylation (H3K27me3) leading to transcription repression (1). However, fundamental insights into both the regulation of PRC2 activity by cofactors as well as the mechanistic principles underlying the spreading of H3K27me3 repressive mark resulting in heterochromatin boundaries remain lacking. Cryo-EM in combination with cross-linking mass spectrometry reveal that cofactors mimic the binding of histone tails to PRC2, and synergistically activate PRC2 through functionally distinct mechanisms (2). In addition, cryo-EM structures of PRC2 bound to di-nucleosome substrates illustrate how the allosteric activation of PRC2 by H3K27me3 mark on one nucleosome results in the trimethylation of histone H3 lysine 27 of the neighboring unmodified nucleosome (3). These foundational results have now paved the way for cryo-EM studies probing the functional crosstalk between multiple histone modifications, for example, inhibition of PRC2 activity by H3K36me3, and the allosteric activation by H2AK119-ubiquitination.

References

1. Vignesh Kasinath, Poepsel, S., Nogales, E. “Recent Insights into Polycomb 

    Repressive Complex 2 Regulation and Substrate Binding”. Biochemistry (2018) DOI:   

   10.1021/acs.biochem.8b01064

2. Vignesh Kasinath, Marco Faini, Simon Poepsel, Dvir Reif, Xinyu Ashlee Feng, Goran    

    Stjepanovic, Ruedi Aebersold, and Eva Nogales. “Structure of human PRC2 with its

    cofactors AEBP2 and JARID2”. Science, 359(6378), 940-944 (2018).

3. Simon Poepsel, Vignesh Kasinath, and Eva Nogales. “Cryo-EM structures of PRC2

    simultaneously engaged with two functionally distinct nucleosomes.” Nat. Struct. Mol.

    Biol., 25(2), 154-162 (2018).