Evidence from flagelliform silk cDNA for the structural basis of elasticity and modular nature of spider silks
Evidence from flagelliform silk cDNA for the structural basis of elasticity and modular nature of spider silks
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DOI：
10.1006/jmbi.1997.1478
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发表时间：
1998-02-06
影响因子：
5.6
通讯作者：
Lewis, RV
中科院分区：
文献类型：
--
作者：
Hayashi, CY;Lewis, RV
圆网蜘蛛依靠它们的空中网来诱捕飞行的猎物。圆网设计的一个关键机械特性是捕获螺旋的高弹性。本文报道了形成捕丝螺旋核心纤维的鞭毛腺丝蛋白的大量cDNA克隆。像所有蚕丝一样，鞭毛状蛋白主要由重复序列组成。该蛋白的显性重复序列为Gly-Pro-Gly-Gly-X，在串联序列中最多可出现63次。该基序可能形成Pro(2)-Gly(3) II型β -旋，由此产生的一系列串联β -旋被认为形成β -螺旋。我们提出，这种弹簧般的螺旋是丝绸弹性的基础。基序(X)可变的第5个位置被一小部分残基（Ala, Ser, Tyr, Val）占据。此外，这些X氨基酸在整个重复序列中以特定的模式出现。这种有序的变化强烈表明，在水合作用下，β -螺旋形成了氢键网络，从而增加了鞭毛状丝的弹性。鞭毛状蛋白单体在丝纤维中的自组装可能受到-螺旋/ -螺旋相互作用的促进。此外，鞭毛状蛋白中的另外两个基序，Gly-Gly-X和一个破坏富含甘氨酸区域的间隔物，可能有助于单体排列成纤维。将该鞭毛状蛋白cDNA与蜘蛛丝基因家族的其他成员进行了比较。我们发现所有的蛛丝蛋白都可以被表征为一组共享的结构模块。这些模块在蛋白质中的出现与从c端区域推断的系统发育关系不一致。这一观察结果，以及单个鞭毛状蛋白重复序列之间的高度变异，但在其他丝蛋白中却明显缺乏这种变异，表明不寻常的均质化过程参与了丝蛋白的进化。(C) 1998学术出版社有限公司
Orb-web weaving spiders rely on their aerial nets to entrap flying prey. A key mechanical feature of orb-web design is the high elasticity of the capture spiral. We report the cloning of substantial cDNA for flagelliform gland silk protein, which forms the core fiber of the catching spiral. Like all silks, the flagelliform protein is composed largely of iterated sequences. The dominant repeat of this protein is Gly-Pro-Gly-Gly-X, which can appear up to 63 times in tandem arrays. This motif likely forms Pro(2)-Gly(3) type II beta-turns and the resulting series of concatenated beta-turns are thought to form a beta-spiral. We propose that this spring-like helix is the basis for the elasticity of silk. The variable fifth position of the motif (X) is occupied by a small subset of residues (Ala, Ser, Tyr, Val). Moreover, these X amino acids occur in specific patterns throughout the repeats. This ordered variation strongly suggests that with hydration, the beta-spirals form hydrogen-bonded networks that increase the elasticity of flagelliform silk. The self-assembly of flagelliform protein monomers into silk fibers may be promoted by beta-spiral/beta-spiral interactions. Additionally, the other two motifs in the flagelliform protein, Gly-Gly-X and a spacer that disrupts the glycine-rich regions, may contribute to the alignment of monomers into fibers.The flagelliform protein cDNA was compared to the other members of the spider silk gene family. We show that all spider silk proteins can be characterized as sets of shared structural modules. The occurrence of these modules among the proteins is inconsistent with the phylogenetic relationships inferred from the C-terminal regions. This observation, along with the high level of variation among individual flagelliform protein repeats, but striking lack of such variation in the other silk proteins, suggests that unusual homogenization processes are involved in silk protein evolution. (C) 1998 Academic Press Limited.