@misc{oai:repo.qst.go.jp:00083354,
 author = {西久保, 開 and Kai, Nishikubo},
 month = {Sep},
 note = {Phosphorylation regulates activation of proteins that repair DNA damage caused by ionizing radiation. XRCC4 is a key protein for the repair to form a multimeric scaffold that connects DNA and LigIV. It is known that at least five phosphorylation sites are localized to the C-terminal side. However, it is not clear how phosphorylation contributes to the regulation of XRCC4 activity.  We hypothesized that a negative charge provided by phosphorylation alters the local static charge distribution of this molecule, causing its conformational changes and turning the activation switch on. In this study,  the structural changes occurring in XRCC4 was investigated using circular dichroism (CD) spectroscopy. Analyzing obtained CD spectra revealed that proportion of α-helix in all secondary structures of the XRCC4 dimer or multimer was 45% or 38%, for β-strand 9% or 15%, respectively. Presumably, α-helix may interfere with the multimerization and β-strand may stabilize it  by the hydrogen bonding. For further investigation of the structural change by phosphorylation, we prepared XRCC4 mutants with a substitution of a residue which are phosphorylated with an aspartic acid that provides similar negative charge distribution to that for wildtype protein. The mutant dimers showed similar structures. For the multimers, α-helix proportion in the mutants decreased by 5% and β-strand proportion increased by 5%, compared to that for wild type. The phosphorylation would facilitate the multimerization, stabilize the multimeric scaffold and promote the DNA repair process., 日本放射線影響学会第64回大会},
 title = {Structural changes in XRCC4 mutants mimicking phosphorylation},
 year = {2021}
}