Anisotropic diffusion of point defects in a two-dimensional crystal of streptavidin observed by high-speed atomic force microscopy
Anisotropic diffusion of point defects in a two-dimensional crystal of streptavidin observed by high-speed atomic force microscopy
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DOI：
10.1088/0957-4484/19/38/384009
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发表时间：
2008-08
期刊：
影响因子：
3.5
通讯作者：
D. Yamamoto;T. Uchihashi;N. Kodera;T. Ando
中科院分区：
文献类型：
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作者：
D. Yamamoto;T. Uchihashi;N. Kodera;T. Ando
用高速原子力显微镜观察了在含生物素的支撑脂质双层膜上形成的二维链霉亲和素晶体中单个点缺陷的扩散。单空位缺陷的二维扩散表现出与正交C 222晶体中的两个晶轴相关的各向异性;在2D平面中，一个轴（a轴）由连续的生物素结合的亚基对组成，而另一个轴（b轴）由连续的生物素未结合的亚基对组成。沿着b轴的扩散率比沿沿着a轴的扩散率大约大2.4倍。这种各向异性归因于生物素结合的亚基-亚基相互作用和生物素未结合的亚基-亚基相互作用之间的缔合自由能的差异。优选的分子间接触发生在未结合生物素的亚基之间。两种亚基对之间的分子间结合能的差异估计约为0.52 kcal mol−1。点缺陷的另一个观察到的动态行为是两个点缺陷融合成一个更大的缺陷，这比一个点缺陷分裂成更小的缺陷更频繁地发生。点缺陷的扩散系数随着缺陷尺寸的增大而增大。较大缺陷的熔合和较高的扩散率被认为是参与无缺陷晶体形成的机制。
The diffusion of individual point defects in a two-dimensional streptavidin crystal formed on biotin-containing supported lipid bilayers was observed by high-speed atomic force microscopy. The two-dimensional diffusion of monovacancy defects exhibited anisotropy correlated with the two crystallographic axes in the orthorhombic C 222 crystal; in the 2D plane, one axis (the a-axis) is comprised of contiguous biotin-bound subunit pairs whereas the other axis (the b-axis) is comprised of contiguous biotin-unbound subunit pairs. The diffusivity along the b-axis is approximately 2.4 times larger than that along the a-axis. This anisotropy is ascribed to the difference in the association free energy between the biotin-bound subunit–subunit interaction and the biotin-unbound subunit–subunit interaction. The preferred intermolecular contact occurs between the biotin-unbound subunits. The difference in the intermolecular binding energy between the two types of subunit pair is estimated to be approximately 0.52 kcal mol−1. Another observed dynamic behavior of point defects was fusion of two point defects into a larger defect, which occurred much more frequently than the fission of a point defect into smaller defects. The diffusivity of point defects increased with increasing defect size. The fusion and the higher diffusivity of larger defects are suggested to be involved in the mechanism for the formation of defect-free crystals.