Corticosteroid-binding globulin (CBG) is a high-affinity plasma protein that binds glucocorticoids (GCs) and regulates their biological activities. The structural and functional properties of CBG are crucial to understanding the biological actions of GCs in mediating stress responses and the underlying mechanisms. In response to stress, avian CBGs modulate the free and bound fractions of plasma corticosterone (CORT, the main GC), enabling them to mediate the physiological and behavioral responses that are fundamental for balancing the trade-off of energetic investment in reproduction, immunity, growth, metabolism and survival, including adaptations to extreme high-elevation or high-latitude environments. Unlike other vertebrates, avian CBGs substitute for sex hormone-binding globulin (SHBG) in transporting androgens and regulating their bioavailability, since birds lack an Shbg gene. The three-dimensional structures of avian and mammalian CBGs are highly conserved, but the steroid-binding site topographies and their modes of binding steroids differ. Given that CBG serves as the primary transporter of both GCs and reproductive hormones in birds, we aim to review the biological properties of avian CBGs in the context of steroid hormone transportation, stress responses and adaptation to harsh environments, and to provide insight into evolutionary adaptations in CBG functions occurred to accommodate physiological and endocrine changes in birds compared with mammals.

中文翻译：

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禽皮质类固醇结合球蛋白：生理应激反应中的生物学功能和调节机制。

皮质类固醇结合球蛋白（CBG）是一种高亲和力血浆蛋白，可结合糖皮质激素（GCs）并调节其生物活性。CBG的结构和功能特性对于理解GC在介导应激反应和潜在机制中的生物学作用至关重要。为了应对压力，禽类CBG调节血浆皮质酮的游离和结合部分（CORT，主要GC），使它们能够介导生理和行为反应，这对于平衡在生殖，免疫，生长，新陈代谢和生存，包括对极端高海拔或高纬度环境的适应。与其他脊椎动物不同 禽类CBG在运输雄激素和调节其生物利用度方面代替了性激素结合球蛋白（SHBG），因为鸟类缺乏Shbg基因。禽类和哺乳动物CBG的三维结构高度保守，但类固醇结合位点的拓扑结构及其结合类固醇的方式有所不同。鉴于CBG是鸟类中GC和生殖激素的主要转运体，我们旨在综述类固醇激素运输，应激反应和对恶劣环境的适应性背景下禽类CBG的生物学特性，并提供进化适应性的见解与哺乳动物相比，CBG的功能发生变化是为了适应鸟类的生理和内分泌变化。禽类和哺乳动物CBG的三维结构高度保守，但类固醇结合位点的拓扑结构及其结合类固醇的方式有所不同。鉴于CBG是鸟类中GC和生殖激素的主要转运体，我们旨在综述类固醇激素运输，应激反应和对恶劣环境的适应性背景下禽类CBG的生物学特性，并提供进化适应性的见解与哺乳动物相比，CBG的功能发生变化是为了适应鸟类的生理和内分泌变化。禽类和哺乳动物CBG的三维结构高度保守，但类固醇结合位点的拓扑结构及其结合类固醇的方式有所不同。鉴于CBG是鸟类中GC和生殖激素的主要转运体，我们旨在综述类固醇激素运输，应激反应和对恶劣环境的适应性背景下禽类CBG的生物学特性，并提供进化适应性的见解与哺乳动物相比，CBG的功能发生变化是为了适应鸟类的生理和内分泌变化。