Abstract
Ssr4 is a yeast protein from Schizosaccharomyces pombe and is an essential part of the chromatin-remodelling [SWI/SNF and RSC (remodelling the structure of chromatin)] complexes found in S. pombe. These complexes (or their homologues) regulate gene expression in eukaryotic organisms, affecting a large number of genes both positively and negatively. The downstream effects are seen in development, and in humans have implications for disease such as cancer. The chromatin structure is altered by modifying the DNA-histone contacts, thus opening up or closing down sections of DNA to specific transcription factors that regulate the transcription of genes. The Ssr4 sequence has little homology to other sequences in the Protein Data Bank, so the structure was solved using an iodine derivative with SAD phasing. The structure of the N-terminal domain is an antiparallel β-sheet of seven strands with α-helices on one side and random coil on the other. The structure is significantly different to deposited structures and was used as a target in the most recent Critical Assessment of Techniques for Protein Structure Prediction (CASP; https://predictioncenter.org/) competition.
Highlights
Chromatin-remodelling complexes are essential for life and are evolutionarily conserved
These complexes have recently been implicated in cancer progression, either owing to their intrinsic ability for tumour suppression or their ability to alter the expression of tumour-suppression gene products (Roberts & Orkin, 2004)
The native and trypsin-treated proteins were characterized by Differential scanning fluorimetry (DSF), where 0.30 ml of protein at 4 mg mlÀ1 was diluted into a final volume of 20 ml. 0.3 ml of a 1:20 dilution of SYPRO Orange dye (Sigma, catalogue No S5692) was added and the temperature was ramped from 20 to 100C in 0.5C steps in a plate-based real-time PCR machine
Summary
Chromatin-remodelling complexes are essential for life and are evolutionarily conserved. Much of our understanding of the chromatinremodelling process comes from studying the two complexes found in the yeast Saccharomyces cerevisiae: SWI/SNF and RSC The structures of both of these multicomponent machines have recently been determined using cryo-EM (Han et al, 2020; Wagner et al, 2020). These complexes interact with histones and histonevariant components of the eukaryotic chromatin. This meant that there was no molecular-replacement model for this protein structure, so de novo phasing would be required
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