Cross-β amyloid fibrils and membrane-bound β-barrels are two important classes of β-sheet proteins. To investigate whether there are systematic differences in the backbone and sidechain conformations of these two families of proteins, here we analyze the ¹³C chemical shifts of 17 amyloid proteins and 7 β-barrel membrane proteins whose high-resolution structures have been determined by NMR. These 24 proteins contain 373 β-sheet residues in amyloid fibrils and 521 β-sheet residues in β-barrel membrane proteins. The ¹³C chemical shifts are shown in 2D ¹³C–¹³C correlation maps, and the amino acid residues are categorized by two criteria: (1) whether they occur in β-strand segments or in loops and turns; (2) whether they are water-exposed or dry, facing other residues or lipids. We also examine the abundance of each amino acid in amyloid proteins and β-barrels and compare the sidechain rotameric populations. The ¹³C chemical shifts indicate that hydrophobic methyl-rich residues and aromatic residues exhibit larger static sidechain conformational disorder in amyloid fibrils than in β-barrels. In comparison, hydroxyl- and amide-containing polar residues have more ordered sidechains and more ordered backbones in amyloid fibrils than in β-barrels. These trends can be explained by steric zipper interactions between β-sheet planes in cross-β fibrils, and by the interactions of β-barrel residues with lipid and water in the membrane. These conformational trends should be useful for structural analysis of amyloid fibrils and β-barrels based principally on NMR chemical shifts.

交叉β淀粉样蛋白原纤维和膜结合β-桶是β-折叠蛋白的两个重要类别。为了研究这两个蛋白质家族的主链和侧链构象是否存在系统差异，我们在此分析了17 种淀粉样蛋白和 7 种 β-桶膜蛋白的¹³ C 化学位移，其高分辨率结构已通过 NMR 确定。这 24 种蛋白质在淀粉样蛋白原纤维中含有 373 个 β-折叠残基，在 β-桶膜蛋白中含有 521 个 β-折叠残基。¹³ C 化学位移显示在 2D 13 ^C – ¹³C相关图，氨基酸残基按两个标准分类：（1）它们是出现在β链片段中还是出现在环和转角中；(2) 是否遇水或干燥，面对其他残留物或脂质。我们还检查了淀粉样蛋白和β-桶中每种氨基酸的丰度，并比较了侧链旋转异构体群。¹³ _C 化学位移表明，与β-桶相比，淀粉样蛋白原纤维中的疏水性富含甲基的残基和芳香族残基表现出更大的静态侧链构象紊乱。相比之下，含羟基和酰胺的极性残基在淀粉样蛋白原纤维中比在 β-桶中具有更有序的侧链和更有序的主链。这些趋势可以通过交叉β原纤维中β-折叠平面之间的空间拉链相互作用以及β-桶残基与膜中脂质和水的相互作用来解释。这些构象趋势对于主要基于 NMR 化学位移的淀粉样蛋白原纤维和 β-桶的结构分析应该是有用的。