Nucleosome structure
From Proteopedia
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Nucleosomes are the basic building blocks of chromatin fibers. A nucleosome consists of a core containing an octamer of histone proteins and a DNA molecule 146 bp long wound around this core in two complete turns. The histone protein octamer includes four types of proteins: H2A, H2B, H3 and H4. Histone proteins are organized in dimers so:
- Two H3-H4 dimers
- Two H2A-H2B dimers
- Whole octamer
- DNA molecule wound in two complete turns around octamer. Some manganese ions complete the whole structure.
The main secondary structure in histones is alpha helices.
If we highlight the different types of amino acid residues on the protein backbone we can see that negatively charged residues and positively charged residues are arranged so positively charged residues are in peripheral positions, where they can form ionic interactions (salt bridges) with phosphate groups on the DNA molecule. This distribution of electric charges stabilizes the whole structure.
See Also
References
This page is based on 1aoi file from Proteopedia.
1aoi is a 10 chain structure with sequence from Xenopus laevis. The July 2000 RCSB PDB Molecule of the Month feature on Nucleosome by David S. Goodsell is 10.2210/rcsb_pdb/mom_2000_7. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.
