Kanno Takashi, Yamaguchi Keiichi, Naiki Hironobu, Goto Yuji, Kawai Tomoji
Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan.
J Struct Biol. 2005 Feb;149(2):213-8. doi: 10.1016/j.jsb.2004.11.008.
Beta2-Microglobulin (beta2-m) is a major structural component of dialysis-related amyloid fibrils. Kozhukh et al. [J. Biol. Chem. 277 (2002) 1310] prepared a series of peptide fragments of beta2-m by the protease digestion and examined their ability to form amyloid fibrils in citrate buffer at pH 2.5. Among various peptides, a 22-residue K3 peptide corresponding to Ser20-Lys41 spontaneously formed amyloid fibrils in aqueous solution. This peptide also formed amyloid protofibrils in 20% (v/v) 2,2,2-trifluoroethanol (TFE). To investigate the influence of solvent conditions on fibril formation, we studied their structures by atomic force microscopy. In aqueous solution, fibrils had a diameter of 4 or 8 nm and tended to cluster each other. On the other hand, protofibrils in 20% (v/v) TFE had a diameter of 2 nm with no tendency of clustering. Intriguingly, when the K3 protofibrils were transferred from 20% (v/v) TFE to aqueous solution, some of them associated to form thicker fibrils with a diameter of 4-15 nm and a left-handed helical twist. TFE is a hydrophobic solvent, so that hydrophobic interactions between molecules may be weakened. The results suggest that the fibrils in aqueous conditions are formed by the cooperative association of protofibrils at the growing ends of the fibrils, in which hydrophobic interactions play a major role.
β2-微球蛋白（β2-m）是透析相关淀粉样纤维的主要结构成分。科朱赫等人[《生物化学杂志》277（2002）1310]通过蛋白酶消化制备了一系列β2-m的肽片段，并检测了它们在pH 2.5的柠檬酸盐缓冲液中形成淀粉样纤维的能力。在各种肽中，对应于Ser20-Lys41的22个残基的K3肽在水溶液中自发形成淀粉样纤维。该肽在20%（v/v）的2,2,2-三氟乙醇（TFE）中也形成了淀粉样原纤维。为了研究溶剂条件对纤维形成的影响，我们通过原子力显微镜研究了它们的结构。在水溶液中，纤维直径为4或8纳米，并且倾向于相互聚集。另一方面，20%（v/v）TFE中的原纤维直径为2纳米，没有聚集的趋势。有趣的是，当K3原纤维从20%（v/v）TFE转移到水溶液中时，其中一些会结合形成直径为4-15纳米且具有左旋螺旋扭曲的更粗的纤维。TFE是一种疏水性溶剂，因此分子间的疏水相互作用可能会减弱。结果表明，水性条件下的纤维是由原纤维在纤维生长末端的协同结合形成的，其中疏水相互作用起主要作用。
