Department of Chemistry, University at Albany, The State University of New York, Albany, New York.
BioTools, Jupiter, Florida.
Biophys J. 2012 Aug 8;103(3):522-531. doi: 10.1016/j.bpj.2012.04.042.
Fibrils are β-sheet-rich aggregates that are generally composed of several protofibrils and may adopt variable morphologies, such as twisted ribbons or flat-like sheets. This polymorphism is observed for many different amyloid associated proteins and polypeptides. In a previous study we proposed the existence of another level of amyloid polymorphism, namely, that associated with fibril supramolecular chirality. Two chiral polymorphs of insulin, which can be controllably grown by means of small pH variations, exhibit opposite signs of vibrational circular dichroism (VCD) spectra. Herein, using atomic force microscopy (AFM) and scanning electron microscopy (SEM), we demonstrate that indeed VCD supramolecular chirality is correlated not only by the apparent fibril handedness but also by the sense of supramolecular chirality from a deeper level of chiral organization at the protofilament level of fibril structure. Our microscopic examination indicates that normal VCD fibrils have a left-handed twist, whereas reversed VCD fibrils are flat-like aggregates with no obvious helical twist as imaged by atomic force microscopy or scanning electron microscopy. A scheme is proposed consistent with observed data that features a dynamic equilibrium controlled by pH at the protofilament level between left- and right-twist fibril structures with distinctly different aggregation pathways for left- and right-twisted protofilaments.
纤维是富含β-折叠的聚集体，通常由几个原纤维组成，并且可能具有可变的形态，例如扭曲的带状物或扁平状的薄片。这种多态性存在于许多不同的淀粉样相关蛋白和多肽中。在之前的一项研究中，我们提出了另一种淀粉样纤维超分子手性的多态性的存在。两种手性胰岛素多晶型，可通过微小的 pH 变化来可控地生长，表现出相反的振动圆二色性（VCD）谱的符号。在此，我们使用原子力显微镜（AFM）和扫描电子显微镜（SEM）证明，VCD 超分子手性不仅与明显的纤维手性相关，而且与原纤维结构中更深层次的手性组织的超分子手性的方向相关。我们的微观检查表明，正常的 VCD 纤维具有左手扭曲，而反向 VCD 纤维则是扁平状的聚集体，没有明显的螺旋扭曲，这可以通过原子力显微镜或扫描电子显微镜成像观察到。我们提出了一个与观察数据一致的方案，该方案在原纤维水平上通过 pH 控制动态平衡，具有明显不同的左扭转和右扭转原纤维的聚合途径的左手和右手扭曲的纤维结构。
