Many cellular functions rely on stable protein-only or protein-RNA complexes. Deciphering their assembly mechanism is a key question in cell biology. We here focus on box C/D small nucleolar ribonucleoproteins involved in ribosome biogenesis. The mature particles contain four core proteins and a guide RNA. Despite their relatively simple composition, these particles don't self-assemble in eukaryote and the production of a native and functional particle requires a large number of transient other proteins, called assembly factors. We present here ¹³C and ¹⁵N solid-state NMR assignment of yeast 126-residue core protein Snu13 in the context of its 50 kDa pre-complex with assembly factors Rsa1p:Hit1p. In this sample, only one third of the protein is labelled, leading to a low sensitivity. We could nevertheless obtain assignment data for 91% of the residues. Secondary structure derived from our assignments shows that Snu13p overall structure is maintained in the context of the complex. Chemical shift perturbations are analysed to evaluate Snu13p conformational changes and interaction interface upon binding to its partner proteins. While indirect perturbations are observed in the hydrophobic core, we find other good candidate residues belonging to the interaction interface. We describe the role of some Snu13p N-terminal and C-terminal residues, not identified in previous structural studies. These preliminary results will serve as a basis for future interaction studies, especially by adding RNA, to decipher box C/D snoRNP particles assembly pathway.

中文翻译：

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方框C / D snoRNPs：早期50 kDa组装中间体的固态NMR指纹图谱。

许多细胞功能依赖于稳定的仅蛋白质或蛋白质-RNA复合物。破解它们的组装机制是细胞生物学中的关键问题。我们在这里集中于参与核糖体生物发生的盒C / D小核仁核糖核蛋白。成熟的颗粒包含四个核心蛋白和一个指导RNA。尽管它们的组成相对简单，但这些颗粒不会在真核生物中自组装，而天然和功能性颗粒的生产需要大量的瞬时其他蛋白质，称为组装因子。我们在这里展示¹³ C和¹⁵酵母126-残留核心蛋白Snu13在其50 kDa预复合物的情况下具有组装因子Rsa1p：Hit1p的N固态NMR分配。在该样品中，只有三分之一的蛋白质被标记，导致灵敏度低。尽管如此，我们仍可以获得91％残基的赋值数据。从我们的作业中得出的二级结构表明Snu13p的总体结构在复杂环境中得以维持。分析化学位移扰动以评估Snu13p构象变化以及与其伴侣蛋白结合后的相互作用界面。虽然在疏水核中观察到了间接扰动，但我们发现了属于相互作用界面的其他良好候选残基。我们描述了一些Snu13p N末端和C末端残基的作用，在先前的结构研究中未发现。