MASS MAPPING OF MACROMOLECULAR ASSEMBLIES

神经丝（NFs），一种神经元特异性的中间丝亚型 (IF)是轴突的基本结构成分。虽然 建立了NF亚基的序列和二级结构， 亚基更高水平地组织成直径约10 nm的细丝 仍然未知，部分原因是成分的异质性， 在获取本地制剂方面存在困难。扫描透射 电子显微镜（STEM）和平行电子能量损失谱 （PEELS）已被用来测量质量和磷分布 从乌贼巨轴突中分离出来的天然神经纤维 结果发现 鱿鱼NF每个横截面仅含有8个卷曲螺旋异二聚体 (in与重构中间体典型的16个二聚体形成对比 细丝），并且每条重链携带至少40个磷酸 组 结果表明，电子散射测量可以 用于表征亚基组织和磷酸化水平， 相同的蛋白质组装。

Neurofilaments (NFs), a neuron-specific subtype of intermediate filament (IF), are an essential structural component of the axon. Although the sequence and secondary structure of NF subunits are established, the higher-level organization of subunits into ~10-nm- diameter filaments remains unknown, in part due to compositional heterogeneity and difficulties in obtaining native preparations. Scanning transmission electron microscopy (STEM) and parallel electron energy-loss spectroscopy (PEELS) have been used to measure the mass and phosphorus distributions of native NFs isolated from the squid giant axon. It was found that squid NFs contain only eight coiled-coil heterodimers per cross section (in contrast to the 16 dimers typical of reconstituted intermediate filaments), and that each heavy chain carries at least 40 phosphate groups. The results show that electron scattering measurements can be used to characterize subunit organization and phosphorylation levels in the same protein assembly.