以分子動力模擬探討點突變對上皮角蛋白1B結構域疏水作用、分子結構和機械性質之影響

Abstract

人類的上皮角蛋白是一種中間絲，做為維持細胞及整個細胞機械穩定性的骨架。微觀的角蛋白結構的穩定性和機械性質能在宏觀上影響著皮膚的性能。本研究重點關注與罕見皮膚遺傳疾病單純型遺傳性表皮分解水皰症相關的角蛋白K 5/14在1B結構域上的突變點L311R，以及掌蹠角化症相關的角蛋白K 1/10在1B結構域上的兩個突變點F231L和S233L。突變的胺基酸位於疏水口袋-錨固旋鈕區域上或區域周圍，這是一個影響1B結構域中角蛋白或非角蛋白在分層組裝的重要區域。我們使用分子動力學模擬來研究突變對不同層次結構的影響，包含了分子尺度上K 5/14及K 1/10在1B結構域上的異二聚體、四聚體及八聚體。首先，結果顯示野生型和突變型在二聚體層級上整體結構高度相似，僅在局部構型上有些微改變，但在更高組裝層級上表現出不同的微觀結構和力學性質。對於L311R，突變導致了鬆散的二聚體間排列，使突變點有機會自由的擺動，這使四聚體層級機械性質上升，並使八聚體層級機械性質減弱。對於F231L的四聚體和八聚體，末端疏水相互作用和氫鍵的減少導致了機械性質的減弱，結果顯示旋鈕-口袋區域的相互作用被破壞。對於S233L，氫鍵的不均勻分布導致了四聚體機械性質的下降，然而在八聚體點突變間新增了表面暴露的疏水性區塊從而提升了力學表現。此研究使我們對點突變的差異如何導致分子尺度上的構型和機械性質發生變化有了更深入的了解。這些性質的差異可能會影響微觀尺度的角蛋白組裝，並最終導致宏觀尺度的疾病發生。

The epithelial keratin of humans is a type of intermediate filament that serves as a backbone to maintain the stability of the cell nucleus as well as for the mechanical stability of whole cells. The stability and mechanical properties of the microscopic keratin structure affect the performance of skin at the macroscopic scale. This study focused on point mutation, L311R, on the keratin 5/14 1B domain related to the rare skin genetic disease Epidermolysis Bullosa Simplex (EBS), and two single-point mutants, F231L and S233L, on the keratin 1/10 1B domain related to the rare skin genetic disease palmoplantar keratoderma (PPK). We used molecular dynamics simulation to study the mutation effect on the different hierarchical structures, including heterodimers, tetramers, and octamers of the K 5/14, and K1/10 1B domain at the atomistic scale. First, the results show that the wild type and mutants are highly similar at the dimer level but exhibit different microstructure and mechanics at the higher-level assembly. For L311R, the mutation resulted in a loose inter-dimer arrangement, giving the mutation point a chance to wiggle freely, which increased the mechanical properties of the tetramer level and weakened the octamer level. For F231L tetramer and octamer, decreased hydrophobic interaction and hydrogen bonds at the terminus results in weakened mechanical properties. The asymmetrical S233L tetramer structure with the uneven distribution of hydrogen bonds decreases its mechanical properties. However, S233L provides extra hydrophobic interactions between the point mutation in octamer, leading to improved mechanical properties. The analysis has given us a deeper understanding of how the differences in point mutations lead to changes in the configuration and mechanical properties at the molecular scale. The difference in these properties might affect the keratin assembly at the microscopic scale and ultimately cause the diseases at the macroscopic scale.