Analytical Department of LFB Biotechnologies, Courtabœuf, France.
Protein Sci. 2019 Nov;28(11):1982-1992. doi: 10.1002/pro.3733.
Human serum albumin (HSA) is the most abundant protein in plasma and presents the particularity, with IgG, to have an extraordinary long serum half-life conferred by its interaction with the neonatal Fc receptor (FcRn). If the impact of IgG post-translational modifications (PTMs) on FcRn binding is well documented, it is far less reported for HSA despite numerous PTMs occurring on the protein in plasma. HSA is susceptible to numerous degradation reactions in plasma, because of aging, oxidative stress or liver and pancreas related pathologies. In the present study, we combined FcRn affinity chromatography and mass spectrometry to investigate the impact of HSA PTMs upon FcRn binding. This methodology presents the advantage to distinguish the effect of a single modification from a plasma HSA preparation made of a mixture of different isoforms. Cys oxidation, Lys glycation, and Leu C-terminal truncation, which are modifications related to several pathological conditions, were demonstrated to act negatively on HSA-FcRn interaction. The HSA-FcRn binding alteration generated by these modifications is consistent with their vicinity with the interaction interface of the two proteins. Results were discussed regarding altered half-life of HSA observed in several disease states and pave the way toward new understandings of the hypoalbuminemia pathogenesis. SIGNIFICANCE STATEMENT: In this study, we investigated the impact of several post-translational modifications of HSA toward its ability to bind to the neonatal Fc receptor using in vitro affinity chromatography, mass spectrometry, and surface plasmon resonance. Cys34 oxidation, Lys525 glycation, and Leu585 C-terminal truncation were demonstrated to decrease HSA-FcRn binding. These modifications occurring in circulating HSA were discussed in relation to several pathologies as well as for the use of HSA as a therapeutic protein.
人血清白蛋白（HSA）是血浆中含量最丰富的蛋白质，具有与 IgG 相同的特点，即与新生 Fc 受体（FcRn）相互作用使其血清半衰期异常延长。虽然 IgG 翻译后修饰（PTMs）对 FcRn 结合的影响已有大量文献记载，但对于 HSA，尽管其在血浆中发生了许多 PTMs，却鲜有报道。由于衰老、氧化应激或肝脏和胰腺相关疾病，HSA 在血浆中易发生多种降解反应。在本研究中，我们结合了 FcRn 亲和层析和质谱技术，研究了 HSA PTMs 对 FcRn 结合的影响。该方法的优点是可以区分单个修饰对 FcRn 结合的影响，以及由不同异构体混合物组成的血浆 HSA 制剂的影响。已证明 Cys 氧化、Lys 糖基化和 Leu C 末端截断等与几种病理状况相关的修饰会对 HSA-FcRn 相互作用产生负面影响。这些修饰引起的 HSA-FcRn 结合改变与其在两种蛋白质相互作用界面的位置一致。这些结果与在几种疾病状态下观察到的 HSA 半衰期改变有关，为进一步理解低白蛋白血症的发病机制铺平了道路。意义：在这项研究中，我们使用体外亲和层析、质谱和表面等离子体共振技术，研究了 HSA 的几种翻译后修饰对其与新生 Fc 受体结合能力的影响。Cys34 氧化、Lys525 糖基化和 Leu585 C 末端截断被证明会降低 HSA-FcRn 的结合。这些在循环 HSA 中发生的修饰与几种病理状况以及 HSA 作为治疗性蛋白质的应用有关。
