很多蛋白在高濃度時都形成纖維狀結(jié)構(gòu)，但蜘蛛網(wǎng)蛋白（有高度重復(fù)片段,，側(cè)面為非重復(fù)性末端區(qū)域）卻有不同行為,。它們在存放于高濃度時具有非常好的可溶性,，但可根據(jù)需要轉(zhuǎn)化成極為堅(jiān)固的纖維。使這一點(diǎn)成為可能的分子機(jī)制尚不清楚,，但本期Nature上兩篇結(jié)構(gòu)研究論文提供了新線索,。
Askarieh等人發(fā)表了來自一種名為“Euprosthenops australis”的織網(wǎng)蜘蛛的一個拖絲蛋白“蜘蛛絲蛋白”的N-端區(qū)域的1.7X-射線晶體結(jié)構(gòu)。該結(jié)構(gòu)顯示了這種高度保守的區(qū)域何以能夠通過防止蜘蛛絲蛋白的過早積累,、以及通過在pH值降低時沿蜘蛛絲伸出管觸發(fā)聚合反應(yīng)來調(diào)控蜘蛛絲的組裝,。
Hagn等人確定了來自常見園蛛科蜘蛛“Araneus diadematus”的拖絲蛋白“絲心蛋白-3”的C-端NR區(qū)域的溶液結(jié)構(gòu)。他們觀察到了該蛋白的存儲和組裝形式之間由化學(xué)或機(jī)械刺激激發(fā)的一個構(gòu)形切換,。（生物谷Bioon.com）
生物谷推薦原文出處：
Nature doi:10.1038/nature08962
Self-assembly of spider silk proteins is controlled by a pH-sensitive relay
Glareh Askarieh1,2,5, My Hedhammar3,5, Kerstin Nordling3, Alejandra Saenz4, Cristina Casals4, Anna Rising3, Jan Johansson3 & Stefan D. Knight2
1Department of Chemistry, Oslo University, 1033 Blindern, 0315 Oslo, Norway
2Department of Molecular Biology, Uppsala BioCenter, SLU, Biomedical Centre, P.O. Box 590, SE-751 24 Uppsala, Sweden
3Department of Anatomy, Physiology and Biochemistry, SLU, Biomedical Centre, P.O. Box 575, SE-751 23 Uppsala, Sweden
4Department of Biochemistry and Molecular Biology I & CIBER Enfermedades Respiratorias, Complutense University of Madrid, 28040-Madrid, Spain
5These authors contributed equally to this work
Nature’s high-performance polymer, spider silk, consists of specific proteins, spidroins, with repetitive segments flanked by conserved non-repetitive domains1, 2. Spidroins are stored as a highly concentrated fluid dope. On silk formation, intermolecular interactions between repeat regions are established that provide strength and elasticity3, 4. How spiders manage to avoid premature spidroin aggregation before self-assembly is not yet established. A pH drop to 6.3 along the spider’s spinning apparatus, altered salt composition and shear forces are believed to trigger the conversion to solid silk, but no molecular details are known. Miniature spidroins consisting of a few repetitive spidroin segments capped by the carboxy-terminal domain form metre-long silk-like fibres irrespective of pH5. We discovered that incorporation of the amino-terminal domain of major ampullate spidroin 1 from the dragline of the nursery web spider Euprosthenops australis (NT) into mini-spidroins enables immediate, charge-dependent self-assembly at pH values around 6.3, but delays aggregation above pH?7. The X-ray structure of NT, determined to 1.7?? resolution, shows a homodimer of dipolar, antiparallel five-helix bundle subunits that lack homologues. The overall dimeric structure and observed charge distribution of NT is expected to be conserved through spider evolution and in all types of spidroins. Our results indicate a relay-like mechanism through which the N-terminal domain regulates spidroin assembly by inhibiting precocious aggregation during storage, and accelerating and directing self-assembly as the pH is lowered along the spider’s silk extrusion duct.
