Department of Biochemistry and Molecular Biology , University of Southern Denmark , 5230 Odense , Denmark.
Biomacromolecules. 2019 Jun 10;20(6):2384-2391. doi: 10.1021/acs.biomac.9b00368. Epub 2019 May 22.
Spider silk's mechanical properties make it an interesting material for many industrial applications. The structure and nanoscopic organization of its proteins are the basis of these qualities. In this study, the emission maxima of the autofluorescence from the protein core of major and minor ampullate silk fibers from the orb-web-weaving spider Nephila madagascariensis are determined and found to be 534 ± 11 and 547 ± 19 nm, respectively. Molecular conformational changes during applied strain are observed in both fiber types using two-photon excitation polarization measurements. Our findings showed that within the fibers the autofluorescent dipoles are separated into two distinct populations, one randomly orientated (amorphous regions) and one with aligned dipoles as found in crystalline structures. The crystalline-amorphous ratio was determined, and it was found that the crystalline dipoles made up around 30 and 20% of the autofluorescent dipoles in major and minor ampullate silk fibers, respectively. Using two-photon polarization measurements, it is possible to directly observe that the major and minor ampullate silk fibers structurally adapt to the applied stress, as well as discern different molecular conformational changes between major and minor ampullates. It was seen that the crystalline-amorphous ratio increased, with up to 9% for major fibers and 6% for minor fibers, as strain was applied, suggesting a conformational adaptation of the fiber, interpreted as noncrystalline 3-helices transforming into crystalline β-sheets.
蜘蛛丝的机械性能使其成为许多工业应用的有趣材料。其蛋白质的结构和纳米组织是这些特性的基础。在这项研究中，确定了来自织圆网蜘蛛 Nephila madagascariensis 的大、小囊状丝纤维蛋白核心的自发荧光发射最大值，分别为 534±11nm 和 547±19nm。使用双光子激发偏振测量，观察到在这两种纤维类型中，在施加应变时分子构象发生变化。我们的研究结果表明，在纤维内部，自发荧光偶极子分为两个不同的群体，一个是随机取向的（无定形区域），另一个是在晶体结构中发现的具有取向偶极子的。确定了晶体-无定形的比例，发现大、小囊状丝纤维中的晶体偶极子分别占自发荧光偶极子的约 30%和 20%。使用双光子偏振测量，可以直接观察到大、小囊状丝纤维结构适应所施加的应力，以及区分大、小囊状丝之间的不同分子构象变化。观察到随着应变的施加，晶体-无定形的比例增加，大纤维增加了 9%，小纤维增加了 6%，这表明纤维的构象适应性，解释为无定形的 3 螺旋转化为晶体β-折叠。
