近日,，美國PLoS ONE雜志發(fā)表了中科院上海生命科學(xué)研究院生化與細(xì)胞所胡紅雨課題組的研究論文,。該論文闡述了III型脊髓小腦共濟失調(diào)癥相關(guān)蛋白ataxin-3（AT3）中的串聯(lián)泛素結(jié)合模體（ubiquitin-interaction motif,，UIM）的構(gòu)象變化和UIM與泛素鏈結(jié)合的協(xié)同效應(yīng),。
UIM是一類擁有泛素結(jié)合和促進(jìn)泛素化功能的短肽序列,。UIM存在于許多不同類型的蛋白質(zhì)中,，其氨基酸序列高度保守,。除了與單泛素（mono-Ub）結(jié)合外,，UIM還能夠與多泛素鏈（poly-Ub）結(jié)合。AT3是一種含有多聚谷氨酰胺（polyQ）的蛋白質(zhì)，其polyQ附近有兩個相連的UIM序列（UIM12）,，對于結(jié)合泛素和促進(jìn)底物泛素化有著十分重要的作用,。
宋愛新博士等人利用核磁共振的方法，解析了UIM12在自由狀態(tài)和結(jié)合泛素狀態(tài)下的溶液結(jié)構(gòu),，每一個UIM模體都由一個a-螺旋組成,。當(dāng)UIM12處于自由狀態(tài)時，這兩個螺旋之間沒有固定的取向,，而當(dāng)結(jié)合了泛素后,，這兩個螺旋便形成了典型的螺旋－環(huán)－螺旋（helix-loop-helix）的折疊構(gòu)象。核磁共振動態(tài)學(xué)數(shù)據(jù)也顯示,，當(dāng)UIM12結(jié)合了泛素后,，兩個螺旋間的連接部分變得更為剛性。通過核磁共振化學(xué)位移干擾（CSP）和等溫滴定量熱（ITC）實驗,，發(fā)現(xiàn)UIM12比單獨的UIM1,、UIM2與泛素的結(jié)合力更強；而與結(jié)合單泛素相比,，UIM12更傾向于結(jié)合通過K48或K63連接的二泛素鏈,，并且兩個UIM之間的連接部分對于UIM12與二泛素鏈的結(jié)合起著重要作用。
這些證據(jù)表明,，UIM12的連接區(qū)域通過構(gòu)象和動態(tài)性質(zhì)的變化,，使兩個UIM模體以協(xié)同效應(yīng)的方式與單泛素或二泛素鏈結(jié)合，這也許與蛋白質(zhì)識別不同類型的多泛素鏈和泛素化底物有關(guān),。
該項研究與上海藥物所林東海課題組合作完成,，工作得到了國家科技部、基金委,、中國科學(xué)院的經(jīng)費支持,。（生物谷Bioon.com）
生物谷推薦英文摘要：
PLoS ONE 5(10): e13202. doi:10.1371/journal.pone.0013202
Structural Transformation of the Tandem Ubiquitin-Interacting Motifs in Ataxin-3 and Their Cooperative Interactions with Ubiquitin Chains
Ai-Xin Song1, Chen-Jie Zhou1, Yu Peng2, Xue-Chao Gao1, Zi-Ren Zhou1, Qing-Shan Fu1, Jing Hong2, Dong-Hai Lin2*, Hong-Yu Hu1*
1 State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China, 2 Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
The ubiquitin-interacting motif (UIM) is a short peptide with dual function of binding ubiquitin (Ub) and promoting ubiquitination. We elucidated the structures and dynamics of the tandem UIMs of ataxin-3 (AT3-UIM12) both in free and Ub-bound forms. The solution structure of free AT3-UIM12 consists of two α-helices and a flexible linker, whereas that of the Ub-bound form is much more compact with hydrophobic contacts between the two helices. NMR dynamics indicates that the flexible linker becomes rigid when AT3-UIM12 binds with Ub. Isothermal titration calorimetry and NMR titration demonstrate that AT3-UIM12 binds diUb with two distinct affinities, and the linker plays a critical role in association of the two helices in diUb binding. These results provide an implication that the tandem UIM12 interacts with Ub or diUb in a cooperative manner through an allosteric effect and dynamics change of the linker region, which might be related to its recognitions with various Ub chains and ubiquitinated substrates.
