主催: Japan Agency for Marine-Earth Science and Technology
共催: Toyo University, Japan Society for the Promotion of Science
Thermococcus kodakaraensis KOD1 possesses two histone molecules, HpkA and HpkB. In vitro study revealed that HpkB possessed higher affinity to DNA and more extensive ability to compact DNA than HpkA. It seems likely that DNA compaction is achieved by tetramerization of dimeric units. Based on structural modeling, tetramer formation by dimer-dimer interaction is considered to require two intermolecular ion pairs formed between histidine and aspartate. In order to examine the role of the ion pairs on DNA compaction, mutant histones were constructed and analyzed using HpkB as a model protein. The mutant histones, HpkB-H50A, HpkB-H50V, and HpkB-H50G were constructed by replacing conserved surface His50 with Ala, Val, and Gly, respectively. Gel mobility shift assays showed that all mutants possessed DNA binding ability, like wild-type HpkB, however all mutants compacted DNA less efficiently than the wild-type. Moreover, all mutants could not maintain the compacted structure of DNA above 80 °C. These results suggest that surface ion pairs between His and Asp play an important role in maintenance of nucleosome structure and DNA stabilization at high temperature.