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下北 啓輔*; 山本 勝宏*; 宮田 登*; 中西 洋平*; 柴田 基樹*; 竹中 幹人*; 山田 悟史*; 瀬戸 秀樹*; 青木 裕之; 宮崎 司*
Soft Matter, 19(11), p.2082 - 2089, 2023/03
被引用回数：0 パーセンタイル：0(Chemistry, Physical)In the case of poly(methyl methacrylate) (PMMA) thin films on a Si substrate, thermal annealing induces the formation of a layer of PMMA chains tightly adsorbed near the substrate interface, and the strongly adsorbed PMMA remains on the substrate, even after washing with toluene (hereinafter called adsorbed sample). Neutron reflectometry revealed that the concerned structure consists of three layers: an inner layer (tightly bound on the substrate), a middle layer (bulk-like), and an outer layer (surface) in the adsorbed sample. When an adsorbed sample was exposed to toluene vapor, it became clear that, between the solid adsorption layer (which does not swell) and bulk-like swollen layer, there was a "buffer layer" that could sorb more toluene molecules than the bulk-like layer. This buffer layer was found not only in the adsorbed sample but also in the standard spin-cast PMMA thin films on the substrate. When the polymer chains were firmly adsorbed and immobilized on the Si substrate, the freedom of the possible structure right next to the tightly bound layer was reduced, which restricted the relaxation of the conformation of the polymer chain strongly. The "buffer layer" was manifested by the sorption of toluene with different scattering length density contrasts.
下北 啓輔*; 山本 勝宏*; 宮田 登*; 有馬 寛*; 中西 洋平*; 竹中 幹人*; 柴田 基樹*; 山田 悟史*; 瀬戸 秀樹*; 青木 裕之; et al.
Langmuir, 38(41), p.12457 - 12465, 2022/10
被引用回数：0 パーセンタイル：0(Chemistry, Multidisciplinary)We measured the neutron reflectivity (NR) of isotactic polypropylene (PP) thin films deposited on Si substrates modified by hexamethyldisilazane (HMDS) at the saturated vapor pressure of deuterated water at 25
C and 60C/85% RH to investigate the effect of HMDS on the interfacial water accumulation in PP-based polymer/inorganic filler nanocomposites and metal/resin bonding materials. We found that the amount of water accumulated at the PP/Si interface decreased with increasing immersion time of the Si substrate in a solution of HMDS in hexane prior to PP film deposition. During the immersion of the Si substrate, the HMDS molecules were deposited on the Si substrate as a monolayer without aggregation. Furthermore, the coverage of the HMDS monolayer on the Si substrate increased with increasing immersion time. At 60C and 85% RH, only a slight amount of interfacial water was detected after HMDS treatment for 1200 min. As a result, the maximum concentration of interfacial water was reduced to 0.1 from 0.3, where the latter corresponds to the PP film deposited on the untreated substrate.
宮崎 司*; 下北 啓輔*; 山本 勝宏*; 青木 裕之; 山田 悟史*; 宮田 登*
Langmuir, 36(49), p.15181 - 15188, 2020/12
被引用回数：6 パーセンタイル：31.74(Chemistry, Multidisciplinary)We investigated the polymer chain dynamics in a 2-3 nm thick poly(vinyl acetate) (PVAc) adsorption layer on a Si substrate with a native oxide layer via neutron reflectometry combined with toluene vapor-induced swelling. We can investigate the polymer chain dynamics difference in the film thickness direction by the difference in the degree of swelling of the polymer layers detected by neutron reflectometry. The mobility of the polymer chains depends on the distance from the substrate. The results elucidated that the interfacial layer with a thickness of approximately 1 nm did not swell at all with toluene vapor, which is a solvent for PVAc. Meanwhile, the surface layer excessively swells with toluene vapor compared to the bulk. This indicates that the polymer chain within the interfacial region is immobilized by the substrate through hydrogen-bonding interaction, but in the surface region, the surface effect overcomes this interfacial interaction. We concluded that the polymer chains in the adsorption layer are either strongly constrained to the substrate, owing to hydrogen bonding, or more mobile than the bulk, owing to the surface effect.
泉 雄大; 山本 悟史*; 藤井 健太郎; 横谷 明徳
放射線生物研究, 51(1), p.91 - 106, 2016/03
放射線などのストレス応答に対する細胞内のタンパク質反応ネットワークの調整機構の解明に大きな威力を発揮すると考えられる円二色性(CD)スペクトル測定の実験、解析方法の解説を行うと共に、われわれがCDスペクトル測定により同定したヒストンタンパク質H2A, H2BのDNA損傷誘起二次構造変化について紹介した。
泉 雄大; 山本 悟史*; 藤井 健太郎; 横谷 明徳
Radiation Research, 184(5), p.554 - 558, 2015/11
被引用回数：7 パーセンタイル：33.11(Biology)We measured and compared the circular dichroism (CD) spectra and secondary structures of histone proteins H2A, H2B, and their variants extracted from X-irradiated and unirradiated human HeLa cells. Compared to unirradiated cells, a relative increase in 
-helix structure and decrease in other secondary structures was observed in X-irradiated cells. These structural alterations persisted for at least 24 hours, which is substantially longer than the 2 hours generally known to be required for DNA double strand break repair.
泉 雄大; 山本 悟史*; 藤井 健太郎; 横谷 明徳
no journal, ,
In a unit chromatin architecture of eukaryotic cells, DNA wraps around histone proteins. It has been gradually recognized that chemical modifications of histones play important roles in DNA repair processes. Kinds of modifications and the functions of modified histones are widely studied, but the conformation of modified histone has not been studied well. In this work, we investigated the secondary structural change of histone H2A/H2B induced by X-ray irradiation to living cells, measuring circular dichroism (CD) spectra. The CD spectra show that -helix structure relatively increased in the X-irradiated cells. The secondary structural change would be induced by chemical modifications of histone H2A/H2B. This structural change may also play important roles in DNA repair processes.
山本 悟史; 泉 雄大; 藤井 健太郎; 横谷 明徳
no journal, ,
DNA鎖が放射線により切断されると、その切断箇所にDNA修復酵素が素早く誘導されるがその誘導メカニズムの詳細はまだ明らかにされていない部分が多い。過去の研究により、染色体中ではDNA分子に生じた2本鎖切断部位近傍のヒストンタンパク質が特異的にリン酸化を受けることが知られている。我々は、このような化学修飾によりヒストン中のへリックスやシートなどの2次構造が変化することで、これをターゲットにDNA修復酵素が損傷部位に誘導されるという作業仮説を立てた。これを証明するため、ヒトがん細胞(HeLa細胞)に大線量(40Gy)のX線を照射し、DNAに大量の2本鎖切断を誘発させた後の照射細胞及び未照射の細胞からヒストンを抽出し、円偏光二色性(CD)スペクトル分析を行った。CD測定は、タンパク質の様々な2次構造に特異的なスペクトルを与えることが知られている。今回得られた照射細胞由来のヒストンに対するCDスペクトルの解析から、2次構造としてアルファへリックスの場所あるいはその量に変化が現れることが明らかになった。この変化に応じてDNA修復が進行することが推測される。
泉 雄大; 山本 悟史*; 藤井 健太郎; 横谷 明徳
no journal, ,
真核生物のDNAは、H2A, H2B, H3, H4と呼ばれるサブユニットから構成されるヒストンタンパク質に巻き付いて存在している。本研究では、損傷したDNAの修復過程におけるヒストンタンパク質の構造変化を調査するために、X線を照射した細胞からH2AとH2Bを抽出し、タンパク質の二次構造変化に敏感な円二色性(CD)スペクトルの測定を行った。CDスペクトルの解析により、X線を照射した細胞から抽出したヒストンH2A/H2Bは、未照射の場合に比べ、-ヘリックス構造が相対的に増加していることが確認された。このような構造変化が損傷修復過程にどのように寄与しているのかは今のところ不明であるが、修復タンパク質を損傷個所に誘導する目印として機能している可能性が考えられる。
山本 悟史; 泉 雄大; 藤井 健太郎; 横谷 明徳
no journal, ,
放射線により細胞核中に生じたDNAの二本鎖切断は、その多くが複数の修復経路で効率よく修復されることが知られている。DNA損傷部位近傍のヒストンが化学修飾を受けることにより立体構造が変化し、これをターゲットにしてDNA修復酵素が損傷部位に誘導されると推測される。そこで本研究では、DNA損傷部位のヒストンの化学修飾により、どのようなタンパク質の立体構造の変化が起きているのかを明らかにすることを目的とした。ヒト細胞にX線を照射し細胞核内のDNAに損傷を誘発した後、細胞から抽出したヒストンに対して円偏光二色性(CD)スペクトル測定を行い2次構造を解析した。その結果、へリックス構造が有意に増加することを見出した。このような二次構造変化は、クロマチン修復ダイナミクスと深く関連している可能性がある。
泉 雄大; 藤井 健太郎; 山本 悟史*; 松尾 光一*; 横谷 明徳
no journal, ,
DNA wraps around core histone proteins composed of several subunits named as H2A, H2B, H3, and H4 in eukaryotic nuclei. It has been gradually recognized that chemical modifications of histones play important roles in DNA repair processes. Recently, we observed relative increment of -helix structure of H2A and H2B (H2A-H2B) induced by X-ray irradiation to human cells. In this work, we investigated structural alterations of H3 and H4 (H3-H4) extracted from X-irradiated cells using vacuum ultraviolet circular dichroism (VUV-CD) spectroscopy. The VUV-CD spectral shape of H3-H4 extracted from X-irradiated cells was different from that from unirradiated cells. Analyzing the CD spectra, we found that -helix structure component of H3-H4 relatively decreased by X-irradiation to cells. This is an opposite of structural change observed in H2A-H2B. The mechanism of histone structural alterations in response to X-ray irradiation has not been identified yet, but a possible mechanism could be via post-translational modifications which are known to occur in histones during DNA damage responses. Cyclopedic VUV-CD spectroscopy of specific modified-histones to understand the alteration mechanism and its contribution to DNA repair processes is warranted for future studies.
泉 雄大; 山本 悟史*; 藤井 健太郎; 横谷 明徳
no journal, ,
DNA wraps around core histone proteins composed of several subunits, named as H2A, H2B, H3, and H4, in eukaryotic nuclei. The knowledge that histones play a substantial role in DNA damage responses (DDRs), such as DNA repair, has increased over time. However, dynamics of histones in chromatin during DDRs is still an open question. In this work, we measured circular dichroism (CD) spectra, which are sensitive to structural changes in proteins, of H2A and H2B (H2A-H2B) extracted from X-irradiated human cells to investigate whether DDRs induce structural alterations of histones. The CD spectra show that -helix content of H2A-H2B in X-irradiated cells is larger than that in unirradiated cells. In contrast, -helix content of X-irradiated H2A-H2B decreased comparing to that of H2A-H2B in unirradiated cells. This result shows that increment of -helix structure of H2A-H2B observed in X-irradiated cells is not induced by prompt X-ray damage. Therefore, we concluded that DDRs, such as DNA damage repair processes, induced the structural alterations of H2A-H2B.
