Solution structural behaviors of ATTCT repeats

M.Phil.Penta-nucleotide ATTCT repeat expansion is associated with spinocerebellar ataxia type 10 (SCA10), which is an autosomal dominant inherited neurodegenerative disorder and yet no therapeutic treatment of this disease is available. In this study, we use high-resolution nuclear magnetic resonance (NMR) spectroscopy to elucidate the solution structural behaviors of ATTCT repeats.Our NMR results show that two ATTCT repeats have a tendency to fold into a mini-dumbbell (MDB) structure containing a regular TTCTA penta-loop and a quasi TTCT/A penta-loop with extensive intra- and inter-loop interactions in a buffer solution containing 10 mM sodium phosphate (pH 7.0). The TTCTA MDB potentially plays an important role in serving as slippage intermediate during DNA replication, thus providing a pathway for the occurrence of ATTCT repeat expansions. Besides, solution structural studies of longer ATTCT repeats have also been studied. Our results show that longer ATTCT repeats show a tendency to form the TTCTA MDB using their first two ATTCT repeats at the 5’-end. With this preferential formation of the TTCTA MDB in longer ATTCT repeats, a potential pathway for the TTCTA MDB escaping from the mismatch repair (MMR) has been proposed.In order to elucidate the 5’-end preferential formation of the TTCTA MDB, the flanking residue effects on the TTCTA MDB have also been studied. Our results show that the 5’ flanking residues are more destabilizing than the 3’ flanking residues on the TTCTA MDB structure. This difference provides a possible explanation on the preferential formation of the TTCTA MDB at the 5’-end of ATTCT repeats. In all, the results from our solution structural investigations provide deeper insights into the genetic instability in ATTCT repeats that enhances our understanding of the origin of SCA10.五去氧核糖核苷酸ATTCT重複序列序列擴增是一種常染色體顯性遺傳神經萎縮症——第十類小腦共濟萎縮症(SCA10)的產生原因。 然而,迄今為止並沒有針對SCA10可行的治療手段。 在本項研究中,高解析度核磁共振波譜被應用於研究溶液狀態下的ATTCT重複序列結構特點。我們的高解析度核磁共振波譜結果顯示, 在10 mM, pH 7.0的磷酸鈉緩衝溶液裡由兩個ATTCT重複序列組成的DNA有趨勢形成由一個TTCTA-五核苷酸DNA環狀結構和另一個TTCT/A-准五核苷酸DNA環狀結構組成的迷你啞鈴狀結構。 這個TTCTA迷你啞鈴狀結構之所以穩定和它大量的環內與環間相互作用是分不開的。 這個TTCTA迷你啞鈴狀結構在DNA複製過程中,可能作為側滑仲介體並且導致雙鏈的錯配,繼而引起ATTCT重複序列的擴增。 除此之外,我們也研究了含有較多ATTCT重複序列的溶液狀態下的結構特點。 結果顯示含有較多ATTCT重複序列的多聚核苷酸在10 mM, pH 7.0的磷酸鈉緩衝溶液裡有趨勢呈現出由5’端的兩個ATTCT序列組成的TTCTA迷你啞鈴狀結構。基於這個TTCTA迷你啞鈴狀結構在的ATTCT重複序列上生成的位置偏好，一個潛在的能使得TTCTA迷你啞鈴狀結構逃離DNA修復的理論被提出。與此同時,為了揭示TTCTA迷你啞鈴狀結構更容易出現在5’端的根本原因,本論文也對相鄰的核酸序列對ATTCT迷你啞鈴狀結構的影響進行了研究。 我們發現,相比于3’端的相鄰核酸序列,5’端的相鄰核酸序列對迷你啞鈴狀結構有更大的破壞性,這為在含有較多ATTCT重複序列的多聚核苷酸上觀察到的TTCTA迷你啞鈴狀結構的位置偏好提供了一種可能的解釋。 總之,本論文的工作對ATTCT重複序列的不穩定性和ATTCT的擴增機理的研究帶去了更深的理解。Zhang, Xi."December 2017."Thesis M.Phil. Chinese University of Hong Kong 2018.Includes bibliographical references (leaves 65-70).Abstracts also in Chinese.Title from PDF title page (viewed on August 11, 2020)