George Papamokos, FORTH Biomedical Research Institute, discusses the cover art he created for the latest issue of Biophysical Journal.
In eykaryotic cells, DNA is packaged within the cell in a state called chromatin. Histones, the main building blocks of chromatin, are among the most highly conserved proteins of eukaryotes. Approximately 147 bp of DNA and an octamer of core histones constitute the nucleosome, the “core particle” of chromatin. The core histones form a globular structure but their N-terminal “tails,” which protrude from the core particle, are unstructured and are thought to fluctuate incessantly. The N-terminal tails can be chemically modified at specific amino acids in their sequence. Posttranslational modifications (PTMs) of histone proteins can either alter the chromatin structure or recruit specific domains of chromatin-associated proteins.
The cover art shows scales of biological matter and events observed on it: 1. the nucleosome core particle with protruding histone tails; 2. heterochromatin Protein 1 (HP1) bound to an H3 methylated oligopeptide, the prototype of PTM-mediated regulation of transcription; and 3. the interaction between residues of the H3 oligopeptide and HP1. The latter was observed after employing full atomistic MD on variably modified structures of HP1 bound to H3, while the former two are crystallographically determined structures. Based on our results and experimental evidence we propose that the 7RKS10 motif is a tertiary functional switch of the H3 tail. Various intrinsically disordered proteins carry this motif as well.
The image was created by George Papamokos, after inspiring talks with Prof. Kaxiras and Prof. Politou. VMD and Adobe Photoshop were used. In the image, nucleosome DNA bps and its histones are displayed in paperchain and surf style, respectively. Each histone dimer is represented in a different color. HP1 chromodomain and H3 oligopeptide are displayed in new ribbons and surf style. In the atomic scale, the interacting residues are displayed in licorice style. Additionally, salt bridges are dotted.
We are very happy that our image was chosen for the cover art of Biophysical Journal. Such exposure of our work gives us the opportunity to expand the network of collaborations and we are always open to such a challenge. Furthermore, it gives us the chance to share a new point of view related to the debate of contemporary biology between those who translate PTMs of histones as a code and those who consider them as a daedal regulatory network: They may additionally be considered as a typical function of intrinsically disordered proteins.
Related work of the contributing labs can be found by interested readers following the links below:
PDB accession codes of nucleosome and HP1-H3 complex: 1AOI and 1KNA