Watson D J, Lander A D, Selkoe D J
Department of Neurology and Program in Neuroscience, Harvard Medical School, and Center for Neurologic Diseases, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
J Biol Chem. 1997 Dec 12;272(50):31617-24. doi: 10.1074/jbc.272.50.31617.
Aggregation and deposition of the 40-42-residue amyloid beta-protein (Abeta) are early and necessary neuropathological events in Alzheimer's disease. An understanding of the molecular interactions that trigger these events is important for therapeutic strategies aimed at blocking Abeta plaque formation at the earliest stages. Heparan sulfate proteoglycans may play a fundamental role since they are invariably associated with Abeta and other amyloid deposits at all stages. However, the nature of the Abeta-heparan sulfate proteoglycan binding has been difficult to elucidate because of the strong tendency of Abeta to self-aggregate. Affinity co-electrophoresis can measure the binding of proteoglycans or glycosaminoglycans to proteins without altering the physical state of the protein during the assay. We used affinity co-electrophoresis to study the interaction between Abeta and the glycosaminoglycan heparin and found that the aggregation state of Abeta governs its heparin-binding properties: heparin binds to fibrillar but not nonfibrillar Abeta. The amyloid binding dye, Congo red, inhibited the interaction in a specific and dose-dependent manner. The "Dutch" mutant AbetaE22Q peptide formed fibrils more readily than wild type Abeta and it also attained a heparin-binding state more readily, but, once formed, mutant and wild type fibrils bound heparin with similar affinities. The heparin-binding ability of aggregated AbetaE22Q was reversible with incubation in a solvent that promotes alpha-helical conformation, further suggesting that conformation of the peptide is important. Studies with another human amyloidogenic protein, amylin, suggested that its heparin-binding properties were also dependent on aggregation state. These results demonstrate the dependence of the Abeta-heparin interaction on the conformation and aggregation state of Abeta rather than primary sequence alone, and suggest methods of interfering with this association.
由40 - 42个氨基酸残基组成的β-淀粉样蛋白（Aβ）的聚集和沉积是阿尔茨海默病早期且必要的神经病理事件。了解引发这些事件的分子相互作用对于旨在最早阶段阻断Aβ斑块形成的治疗策略至关重要。硫酸乙酰肝素蛋白聚糖可能起着根本性作用，因为它们在所有阶段都始终与Aβ及其他淀粉样沉积物相关联。然而，由于Aβ强烈的自我聚集倾向，Aβ与硫酸乙酰肝素蛋白聚糖结合的本质一直难以阐明。亲和共电泳可以测量蛋白聚糖或糖胺聚糖与蛋白质的结合，而在测定过程中不会改变蛋白质的物理状态。我们使用亲和共电泳研究了Aβ与糖胺聚糖肝素之间的相互作用，发现Aβ的聚集状态决定其肝素结合特性：肝素与纤维状而非非纤维状的Aβ结合。淀粉样结合染料刚果红以特异性和剂量依赖性方式抑制这种相互作用。“荷兰”突变体AβE22Q肽比野生型Aβ更容易形成纤维，并且它也更容易达到肝素结合状态，但是，一旦形成后，突变体和野生型纤维以相似的亲和力结合肝素。聚集的AβE22Q的肝素结合能力在促进α-螺旋构象的溶剂中孵育后是可逆的，这进一步表明肽的构象很重要。对另一种人类淀粉样生成蛋白胰岛淀粉样多肽的研究表明，其肝素结合特性也取决于聚集状态。这些结果证明了Aβ与肝素的相互作用依赖于Aβ的构象和聚集状态而非仅依赖于一级序列，并提出了干扰这种关联的方法。
