Menzies Research Institute, University of Tasmania, Hobart, Tasmania, Australia.
J Neurochem. 2010 Mar;112(6):1552-61. doi: 10.1111/j.1471-4159.2010.06571.x. Epub 2010 Jan 7.
The beta-site APP cleaving enzyme (BACE1) is responsible for the first step in the production of the beta-amyloid protein of Alzheimer's disease. BACE1 is synthesized as a partially active zymogen (proBACE1). We previously showed that the glycosaminoglycan (GAG) heparin can increase the enzyme activity of proBACE1. In this study, the structural requirements and the mechanism for the GAG-induced activation were examined. The effect of heparin on proBACE1 was influenced by the degree of sulfation and carboxylation of the GAG, as well as by the length of the sugar. Although low molecular weight heparin fragments did not strongly stimulate proBACE1, they inhibited heparin-induced activation of the enzyme. The structure of the zymogen was modeled using the known X-ray structures of the BACE1 catalytic domain and the homologous prodomain of porcine pepsinogen. The modeled structure suggested that a heparin-binding domain may reside close to the prodomain, and that movement of a loop region between residues 46-65, lying adjacent to the prodomain, may be needed to accommodate heparin binding. The presence of the loop domain adjacent to the active site may account for the lower activity of the zymogen relative to the mature enzyme. Movement of the loop region upon heparin binding could expose the active site region to allow for increased substrate binding. The results suggest a model in which conformational changes close to the prodomain may be involved in the mechanism of heparin-induced activation of proBACE1.
β-位淀粉样前体蛋白裂解酶（BACE1）负责阿尔茨海默病β-淀粉样蛋白的产生的第一步。BACE1 最初合成时为部分活性的酶原（proBACE1）。我们先前表明，糖胺聚糖（GAG）肝素可以增加 proBACE1 的酶活性。在这项研究中，我们研究了 GAG 诱导激活的结构要求和机制。肝素对 proBACE1 的影响受 GAG 的硫酸化和羧化程度以及糖的长度的影响。尽管低分子量肝素片段不能强烈刺激 proBACE1，但它们抑制肝素诱导的酶激活。使用 BACE1 催化结构域和猪胃蛋白酶原同源前结构域的已知 X 射线结构来模拟酶原的结构。模型结构表明，肝素结合域可能位于前结构域附近，并且可能需要位于前结构域附近的残基 46-65 之间的环区域移动，以适应肝素结合。环区域位于活性位点附近的存在可能是酶原相对于成熟酶的活性较低的原因。肝素结合时环区域的移动可能会暴露活性位点区域，从而增加底物结合。结果表明，靠近前结构域的构象变化可能参与肝素诱导 proBACE1 激活的机制。
