雙量子同調性於固態核磁共振儀中的演化與鎖場

近年來蛋白質動態學越來越受人們重視，因為許多研究指出蛋白質的運動與其生物功能性相關，而核磁共振儀為眾多研究蛋白質動態學的方法中最常被使用的儀器之一。在本論文中我們認為雙量子同調性訊號與分子動態有直接關係，因此我們嘗試設計不同的脈衝序列以偵測該訊號於磁場中的演化。我們嘗試了三種方法，其中以脈衝序列 SPC5 激發出雙量子同調性訊號、並再以脈衝序列 R-TOBSY 對訊號進行鎖場的方法有最佳結果。我們運用 R-TOBSY 的對稱性抑制除了 J-耦合之外的作用力，讓雙量子訊號隨鎖場時間的衰減只與系統性自旋-自旋弛緩現象以及分子動態相關。實驗中，樣品 [U-13C]-L-丙胺酸之實驗結果與軟體模擬出的結果吻合，且鎖場時間可長達 6 毫秒，顯示此方法的成功。最後我們將此方法運用於蛋白質 GB1 以及 Bcl-xL，並使用三角與指數之合成函數對訊號擬合，得到各標示峰的雙量子同調性訊號衰減速率。雖然因為光譜解析度不足而無法再進一步與胺基酸位置對應，一旦能克服此問題，此方法將有機會得到蛋白質各部位的動態資訊。

關鍵字

固態核磁共振；核磁共振；雙量子；鎖場

並列摘要

Motional dynamics in polypeptides and proteins are believed to correlate with their biological functions. Such dynamics may be indirectly characterized by probing the double quantum coherence (DQC) signals in NMR. We attempt to generate DQC with pulse sequence SPC5 in solid-state NMR. Three methods have been applied to investigate the evolution of DQC. Among them, the method using R-TOBSY to do spin-locking gave the most favorable results. Effects from the dipolar interactions and chemical shifts are suppressed by the symmetry of R-TOBSY, so that the decay of DQC signals only depend on the transverse spin-spin relaxation properties of the systems. Experimental data from [U-13C]-L-alanine agree with the simulated curves at a spin-locking time up to 6 milliseconds. We then apply this method on protein GB1 and Bcl-xL. The resulted signals are fitted with a mathmatic function including oscillation part and decay part. Though the low resolution of spectra limits the implication of fitting, as long as we conquer this problem the R-TOBSY spin-locking method may be applicable to study the motional dynamics of biomacromolecules.

並列關鍵字

solid state NMR ； NMR ； nuclear magnatic resonance ； double quantum ； spin locking

參考文獻

1. Anfinsen, C. B. Principles that Govern the Folding of Protein Chains. Science 181, 223–230 (1973).

Google Scholar

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