Department of Chemistry, University of Eastern Finland, PO BOX 111, 80100 Joensuu, Finland.
VTT Technical Research Centre of Finland Ltd, Tietotie 2, 02150 Espoo, Finland.
J Struct Biol. 2023 Jun;215(2):107966. doi: 10.1016/j.jsb.2023.107966. Epub 2023 Apr 25.
Cortisol is a steroid hormone that is produced by the adrenal gland. It is a primary stress hormone that increases glucose levels in the blood stream. High concentrations of cortisol in the body can be used as a biomarker for acute and chronic stress and related mental and physiological disorders. Therefore, the accurate quantification of cortisol levels in body fluids is essential for clinical diagnosis. In this article, we describe the isolation of recombinant anti-cortisol antibodies with high affinity for cortisol and discover their cross-reactivity with other glucocorticoids. To describe the cortisol binding site and elucidate the structural basis for the binding specificity, the high-resolution crystal structures of the anti-cortisol (17) Fab fragment in the absence of glucocorticoid (2.00 Å) and the presence of cortisol (2.26 Å), corticosterone (1.86 Å), cortisone (1.85 Å) and prednisolone (2.00 Å) were determined. To our knowledge, this is the first determined crystal structure of a cortisol-specific antibody. The recognition of cortisol is driven by hydrophobic interactions and hydrogen bonding at the protein-ligand interface coupled with a conformational transition. Comparison of ligand-free and ligand-bound structures showed that the side chains of residues Tyr58-H and Arg56-H can undergo local conformational changes at the binding site, most likely prior to the binding event via a conformational selection mechanism. Compared to other anti-steroid antibody-antigen complexes, (17) Fab possesses a structurally unique steroid binding site, as the H3 loop from the CDR area has only a minor contribution, but framework residues have a prominent contribution to hapten binding.
皮质醇是一种由肾上腺产生的类固醇激素。它是一种主要的应激激素，可增加血液中的葡萄糖水平。体内皮质醇浓度升高可用作急性和慢性应激以及相关精神和生理障碍的生物标志物。因此，准确测量体液中的皮质醇水平对于临床诊断至关重要。在本文中，我们描述了具有高亲和力的皮质醇的重组抗皮质醇抗体的分离，并发现了它们与其他糖皮质激素的交叉反应性。为了描述皮质醇结合位点并阐明结合特异性的结构基础，我们测定了抗皮质醇（17）Fab 片段在无糖皮质激素（2.00Å）和存在皮质醇（2.26Å）、皮质酮（1.86Å）、可的松（1.85Å）和泼尼松龙（2.00Å）时的高分辨率晶体结构。据我们所知，这是第一个确定的皮质醇特异性抗体的晶体结构。皮质醇的识别是由疏水相互作用和氢键驱动的，这些相互作用和氢键位于蛋白质-配体界面上，并与构象转变相结合。配体自由和配体结合结构的比较表明，残基 Tyr58-H 和 Arg56-H 的侧链可以在结合部位发生局部构象变化，很可能通过构象选择机制在结合事件之前发生。与其他抗甾体抗体-抗原复合物相比，（17）Fab 具有结构独特的甾体结合部位，因为来自 CDR 区的 H3 环只有很小的贡献，但框架残基对半抗原结合有显著贡献。
