Denys A, Allain F, Carpentier M, Spik G
Laboratoire de Chimie Biologique, Unité Mixte de Recherche du Centre National de Recherche Scientifique no. 111, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France.
Biochem J. 1998 Dec 15;336 ( Pt 3)(Pt 3):689-97. doi: 10.1042/bj3360689.
Cyclophilin B (CyPB) is a cyclosporin A (CsA)-binding protein, mainly associated with the secretory pathway, and is released in biological fluids. We recently reported that CyPB specifically binds to T-lymphocytes and promotes enhanced incorporation of CsA. The interactions with cellular binding sites involved, at least in part, the specific N-terminal extension of the protein. In this study, we intended to specify further the nature of the CyPB-binding sites on peripheral blood T-lymphocytes. We first provide evidence that the CyPB binding to heparin-Sepharose is prevented by soluble sulphated glycosaminoglycans (GAG), raising the interesting possibility that such interactions may occur on the T-cell surface. We then characterized CyPB binding to T-cell surface GAG and found that these interactions involved the N-terminal extension of CyPB, but not its conserved CsA-binding domain. In addition, we determined the presence of a second CyPB binding site, which we termed a type I site, in contrast with type II for GAG interactions. The two binding sites exhibit a similar affinity but the expression of the type I site was 3-fold lower. The conclusion that CyPB binding to the type I site is distinct from the interactions with GAG was based on the findings that it was (1) resistant to NaCl wash and GAG-degrading enzyme treatments, (2) reduced in the presence of CsA or cyclophilin C, and (3) unmodified in the presence of either the N-terminal peptide of CyPB or protamine. Finally, we showed that the type I binding sites were involved in an endocytosis process, supporting the hypothesis that they may correspond to a functional receptor for CyPB.
亲环蛋白B（CyPB）是一种环孢素A（CsA）结合蛋白，主要与分泌途径相关，并释放到生物体液中。我们最近报道，CyPB特异性结合T淋巴细胞并促进CsA的摄取增强。与细胞结合位点的相互作用至少部分涉及该蛋白特定的N端延伸。在本研究中，我们旨在进一步明确外周血T淋巴细胞上CyPB结合位点的性质。我们首先提供证据表明，可溶性硫酸化糖胺聚糖（GAG）可阻止CyPB与肝素-琼脂糖的结合，这引发了一种有趣的可能性，即这种相互作用可能发生在T细胞表面。然后我们对CyPB与T细胞表面GAG的结合进行了表征，发现这些相互作用涉及CyPB的N端延伸，但不涉及其保守的CsA结合结构域。此外，我们确定存在第二个CyPB结合位点，我们将其称为I型位点，与GAG相互作用的II型位点形成对比。这两个结合位点表现出相似的亲和力，但I型位点的表达量低3倍。CyPB与I型位点的结合不同于与GAG的相互作用，这一结论基于以下发现：（1）它对NaCl洗涤和GAG降解酶处理具有抗性；（2）在CsA或亲环蛋白C存在时减少；（3）在CyPB的N端肽或鱼精蛋白存在时未改变。最后，我们表明I型结合位点参与了内吞过程，支持了它们可能对应于CyPB功能性受体的假设。
