Human cystatin C (hCC), a member of the superfamily of papain-like cysteine protease inhibitors, is the most widespread cystatin in human body fluids. This small protein, in addition to its physiological function, is involved in various diseases, including cerebral amyloid angiopathy, cerebral hemorrhage, stroke, and dementia. Physiologically active hCC is a monomer. However, all structural studies based on crystallization led to the dimeric structure formed as a result of a three-dimensional exchange of the protein domains (3D domain swapping). The monomeric structure was obtained only for hCC variant V57N and for the protein stabilized by an additional disulfide bridge. With this study, we extend the number of models of monomeric hCC by an additional hCC variant with a single amino acid substitution in the flexible loop L1. The V57G variant was chosen for the X-ray and NMR structural analysis due to its exceptional conformational stability in solution. In this work, we show for the first time the structural and dynamics studies of human cystatin C variant in solution. We were also able to compare these data with the crystal structure of the hCC V57G and with other cystatins. The overall cystatin fold is retained in the solute form. Additionally, structural information concerning the N terminus was obtained during our studies and presented for the first time. DATABASE: Crystallographic structure: structural data are available in PDB databases under the accession number 6ROA. NMR structure: structural data are available in PDB and BMRB databases under the accession numbers 6RPV and 34399, respectively.

中文翻译：

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核磁共振和晶体结构研究的人半胱氨酸蛋白酶抑制剂C具有单个氨基酸取代的极其稳定的单体变体。

人半胱氨酸蛋白酶抑制剂C（hCC）是木瓜蛋白酶样半胱氨酸蛋白酶抑制剂超家族的成员，是人体液中最广泛的半胱氨酸蛋白酶抑制剂。除了生理功能外，这种小蛋白还参与多种疾病，包括脑淀粉样血管病，脑出血，中风和痴呆。具有生理活性的hCC是单体。但是，所有基于结晶的结构研究都导致由于蛋白质域的三维交换（3D域交换）而形成的二聚体结构。仅对于hCC变体V57N和通过附加的二硫键稳定的蛋白质获得了单体结构。通过这项研究，我们通过柔性环L1中具有单个氨基酸取代的其他hCC变体扩展了单体hCC的模型数量。选择V57G变体进行X射线和NMR结构分析，是因为其在溶液中具有出色的构象稳定性。在这项工作中，我们首次展示了人类半胱氨酸蛋白酶抑制剂C变体在溶液中的结构和动力学研究。我们还能够将这些数据与hCC V57G的晶体结构以及其他半胱氨酸蛋白酶抑制剂进行比较。半胱氨酸蛋白酶抑制剂的整体褶皱以溶质形式保留。此外，有关N末端的结构信息是在我们的研究过程中获得的，并且是首次提出。数据库：晶体结构：结构数据可在PDB数据库中获得，登录号为6ROA。NMR结构：结构数据可在PDB和BMRB数据库中获得，登录号分别为6RPV和34399。