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另一种捕食性丝:萤火虫(双翅目:扁角菌蚊科)所产的丝在大量无定形部分中包含交叉β-折叠微晶。

The other prey-capture silk: Fibres made by glow-worms (Diptera: Keroplatidae) comprise cross-β-sheet crystallites in an abundant amorphous fraction.

作者信息

Walker Andrew A, Weisman Sarah, Trueman Holly E, Merritt David J, Sutherland Tara D

机构信息

Evolution, Ecology and Genetics, Research School of Biology, Australian National University, Canberra, 0200, Australia; Ecosystem Sciences, Commonwealth Scientific and Industrial Research Organisation, Black Mountain Laboratories, Canberra, 2601, Australia.

Ecosystem Sciences, Commonwealth Scientific and Industrial Research Organisation, Black Mountain Laboratories, Canberra, 2601, Australia.

出版信息

Comp Biochem Physiol B Biochem Mol Biol. 2015 Sep;187:78-84. doi: 10.1016/j.cbpb.2015.05.008. Epub 2015 May 22.

Abstract

Glow-worms (larvae of dipteran genus Arachnocampa) are restricted to moist habitats where they capture flying prey using snares composed of highly extensible silk fibres and sticky mucus droplets. Little is known about the composition or structure of glow-worm snares, or the extent of possible convergence between glow-worm and arachnid capture silks. We characterised Arachnocampa richardsae silk and mucus using X-ray scattering, Fourier transform infrared spectroscopy and amino acid analysis. Silk but not mucus contained crystallites of the cross-β-sheet type, which occur in unrelated insect silks but have not been reported previously in fibres used for prey capture. Mucus proteins were rich in Gly (28.5%) and existed in predominantly a random coil structure, typical of many adhesive proteins. In contrast, the silk fibres were unusually rich in charged and polar residues, particularly Lys (18.1%), which we propose is related to their use in a highly hydrated state. Comparison of X-ray scattering, infrared spectroscopy and amino acid analysis data suggests that silk fibres contain a high fraction of disordered protein. We suggest that in the native hydrated state, silk fibres are capable of extension via deformation of both disordered regions and cross-β-sheet crystallites, and that high extensibility is an adaptation promoting successful prey capture. This study illustrates the rich variety of protein motifs that are available for recruitment into biopolymers, and how convergently evolved materials can nevertheless be based on fundamentally different protein structures.

摘要

萤火虫(双翅目蛛萤属幼虫)仅分布于潮湿的栖息地,它们利用由高度可延展的丝纤维和粘性黏液滴组成的陷阱捕获飞行中的猎物。关于萤火虫陷阱的组成、结构,以及萤火虫与蛛形纲动物用于捕获猎物的丝之间可能存在的趋同程度,人们了解甚少。我们利用X射线散射、傅里叶变换红外光谱和氨基酸分析对里氏蛛萤的丝和黏液进行了表征。丝中含有交叉β-折叠片层类型的微晶,而黏液中没有。交叉β-折叠片层微晶存在于不相关的昆虫丝中,但此前尚未在用于捕获猎物的纤维中报道过。黏液蛋白富含甘氨酸(28.5%),主要以无规卷曲结构存在,这是许多黏附蛋白的典型特征。相比之下,丝纤维异常富含带电荷和极性的残基,尤其是赖氨酸(18.1%),我们认为这与它们在高度水合状态下的使用有关。X射线散射、红外光谱和氨基酸分析数据的比较表明,丝纤维含有高比例的无序蛋白。我们认为,在天然水合状态下,丝纤维能够通过无序区域和交叉β-折叠片层微晶的变形实现伸展,并且高伸展性是一种促进成功捕获猎物的适应性特征。这项研究说明了可用于纳入生物聚合物的丰富多样的蛋白质基序,以及趋同进化的材料如何仍然可以基于根本不同的蛋白质结构。

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