Unveiling the interplay between Copper and Heme binding to Hemopexin

Hemopexin (Hpx) is a plasma glycoprotein with very high affinity for heme. It can mitigate heme-mediated oxidative stress and cardiovascular dysfunction and has promising therapeutic applications for hemolytic disorders. The uptake of heme-Hpx is accompanied by an increase in intracellular Cu levels, thus hinting at a dynamic interaction between Cu and Hpx. In vitro studies have indicated that Cu(II) can disrupt heme-Hpx complex formation. Consequently, it has been proposed that Cu(II) binds to Hpx under the acidic endosomal conditions, preventing heme re-binding. This project seeks to elucidate the interplay between Cu and heme binding to Hpx. To this end, X-ray Absorption Spectroscopy will be used for the first time to characterize heme- and Cu-binding sites in Hpx in different pH conditions to understand (i) how Cu(II) is bound at both pH, (ii) whether it can be released upon reduction by physiological agents and (iii) what is the mutual impact of Cu- and heme-binding.

血红素结合蛋白（Hemopexin, Hpx）是一类对血红素具有极高亲和力的血浆糖蛋白。其可缓解血红素介导的氧化应激与心血管功能障碍，在溶血性疾病的治疗中具有良好的应用前景。血红素-血红素结合蛋白复合物的摄取会伴随细胞内铜离子水平的升高，这提示铜离子与血红素结合蛋白之间存在动态相互作用。体外实验表明，铜(II)可破坏血红素-血红素结合蛋白复合物的形成。据此，有研究提出，铜(II)可在酸性内体环境下结合血红素结合蛋白，从而阻止血红素的重新结合。本研究旨在阐明铜离子与血红素在血红素结合蛋白上的结合相互作用。为此，本研究将首次采用X射线吸收光谱法（X-ray Absorption Spectroscopy），对不同pH条件下血红素结合蛋白上的血红素与铜离子结合位点进行表征，以明确以下内容：(i) 铜(II)在两种pH条件下的结合模式；(ii) 其是否可在生理还原剂作用下被释放；(iii) 铜离子结合与血红素结合之间存在何种相互影响。