Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA.
Pharmaceutical Sciences, Merck & Co., Inc., Kenilworth, NJ, USA.
Nat Struct Mol Biol. 2019 Jul;26(7):592-598. doi: 10.1038/s41594-019-0238-6. Epub 2019 Jun 24.
Glucagon and insulin maintain blood glucose homeostasis and are used to treat hypoglycemia and hyperglycemia, respectively, in patients with diabetes. Whereas insulin is stable for weeks in its solution formulation, glucagon fibrillizes rapidly at the acidic pH required for solubility and is therefore formulated as a lyophilized powder that is reconstituted in an acidic solution immediately before use. Here we use solid-state NMR to determine the atomic-resolution structure of fibrils of synthetic human glucagon grown at pharmaceutically relevant low pH. Unexpectedly, two sets of chemical shifts are observed, indicating the coexistence of two β-strand conformations. The two conformations have distinct water accessibilities and intermolecular contacts, indicating that they alternate and hydrogen bond in an antiparallel fashion along the fibril axis. Two antiparallel β-sheets assemble with symmetric homodimer cross sections. This amyloid structure is stabilized by numerous aromatic, cation-π, polar and hydrophobic interactions, suggesting mutagenesis approaches to inhibit fibrillization could improve this important drug.
胰高血糖素和胰岛素分别维持血糖的动态平衡，用于治疗糖尿病患者的低血糖和高血糖。虽然胰岛素在其溶液制剂中可以稳定数周，但在用于溶解的酸性 pH 值下，胰高血糖素会迅速纤维化，因此被配制成冻干粉末，在使用前立即在酸性溶液中复溶。在这里，我们使用固态 NMR 确定了在具有药用相关性的低 pH 值下生长的合成人胰高血糖素纤维的原子分辨率结构。出乎意料的是，观察到两组化学位移，表明存在两种 β-折叠构象。这两种构象具有不同的水可及性和分子间接触，表明它们沿着纤维轴交替并以反平行方式形成氢键。两个反平行的β-折叠片以对称的同源二聚体横截面组装。这种淀粉样结构由许多芳香族、阳离子-π、极性和疏水性相互作用稳定，表明突变体抑制纤维化的方法可能会改善这种重要的药物。
