National Institute of Agrobiological Sciences (NIAS), Tsukuba, Ibaraki 305-8634, Japan.
Laboratory of Electron Microscopy and Crystal Chemistry, Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan.
J Struct Biol. 2014 Mar;185(3):303-8. doi: 10.1016/j.jsb.2013.12.005. Epub 2013 Dec 15.
α-Helical coiled coil and β-sheet complexes are essential structural building elements of silk proteins produced by different species of the Hymenoptera. Beside X-ray scattering at wide and small angles we applied cryo-electron diffraction and microscopy to demonstrate the presence and the details of such structures in silk of the giant hornet Vespa mandarinia japonica. Our studies on the assembly of the fibrous silk proteins and their internal organization in relation to the primary chain structure suggest a 172 Å pitch supercoil consisting of four intertwined alanine-rich α-helical strands. The axial periodicity may adopt even multiples of the pitch value. Coiled coil motifs form the largest portion of the hornet silk structure and are aligned nearly parallel to the cocoon fiber axis in the same way as the membrane-like parts of the cocoon are molecularly orientated in the spinning direction. Supercoils were found to be associated with β-crystals, predominantly localized in the l-serine-rich chain sequences terminating each of the four predominant silk proteins. Such β-sheet blocks are considered resulting from transformation of random coil molecular sequences due to the action of elongational forces during the spinning process.
α-螺旋卷曲螺旋和β-折叠复合物是膜翅目不同物种产生的丝蛋白的基本结构构建元素。除了广角和小角 X 射线散射外，我们还应用冷冻电子衍射和显微镜来证明巨型大黄蜂 Vespa mandarinia japonica 丝中存在这种结构及其细节。我们对纤维状丝蛋白的组装及其与一级链结构的内部组织的研究表明，存在由四个相互缠绕的富含丙氨酸的α-螺旋链组成的 172Å 螺距超螺旋。轴向周期性可能采用螺距值的偶数倍。卷曲螺旋基序构成了大黄蜂丝结构的最大部分，并且与茧纤维轴几乎平行排列，就像茧的膜状部分在纺丝方向上分子取向一样。发现超螺旋与β-晶体有关，β-晶体主要定位于终止四个主要丝蛋白中的每一个的 l-丝氨酸丰富链序列中。由于纺丝过程中拉伸力的作用，这种β-折叠块被认为是由于无规卷曲分子序列的转化而产生的。
