Byeon In-Ja L, Louis John M, Gronenborn Angela M
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
J Mol Biol. 2004 Jul 9;340(3):615-25. doi: 10.1016/j.jmb.2004.04.069.
Immunoglobulin binding domain B1 of streptococcal protein G (GB1), a small (56 residues), stable, single domain protein, is one of the most extensively used model systems in the area of protein folding and design. The recently determined NMR structure of a quadruple mutant (HS#124F26A, L5V/F30V/Y33F/A34F) revealed a domain-swapped dimer that dissociated into a partially folded, monomeric species at low micromolar protein concentrations. Here, we have characterized this monomeric, partially folded species by NMR and show that extensive conformational heterogeneity for a substantial portion of the polypeptide chain exists. Exchange between the conformers within the monomer ensemble on the microsecond to millisecond timescale renders the majority of backbone amide resonances broadened beyond detection. Despite these extensive temporal and spatial fluctuations, the overall architecture of the monomeric mutant protein resembles that of wild-type GB1 and not the monomer unit of the domain-swapped dimer.
链球菌蛋白G（GB1）的免疫球蛋白结合结构域B1是一种小的（56个残基）、稳定的单结构域蛋白，是蛋白质折叠和设计领域中使用最广泛的模型系统之一。最近确定的四重突变体（HS#124F26A、L5V/F30V/Y33F/A34F）的核磁共振结构显示出一种结构域交换二聚体，在低微摩尔浓度的蛋白质条件下会解离成部分折叠的单体形式。在这里，我们通过核磁共振对这种单体、部分折叠的形式进行了表征，并表明多肽链的大部分存在广泛的构象异质性。单体集合内构象异构体之间在微秒到毫秒时间尺度上的交换使得大多数主链酰胺共振变宽到无法检测。尽管存在这些广泛的时间和空间波动，但单体突变蛋白的整体结构类似于野生型GB1，而不像结构域交换二聚体的单体单元。
