Perry David J, Bittencourt Daniela, Siltberg-Liberles Jessica, Rech Elibio L, Lewis Randolph V
Department of Molecular Biology, University of Wyoming, Laramie, Wyoming 821071-3944, United States, Laboratory of Molecular Biology, EMBRAPA Western Amazonia, Manaus, AM, Brazil, and Laboratory of Gene Transfer, Biotechnology Unit, EMBRAPA Genetic Resources and Biotechnology, Brasilia, DF, Brazil.
Biomacromolecules. 2010 Nov 8;11(11):3000-6. doi: 10.1021/bm1007585. Epub 2010 Oct 18.
Orb-weaving spider silk fibers are assembled from very large, highly repetitive proteins. The repeated segments contain, in turn, short, simple, and repetitive amino acid motifs that account for the physical and mechanical properties of the assembled fiber. Of the six orb-weaver silk fibroins, the piriform silk that makes the attachment discs, which lashes the joints of the web and attaches dragline silk to surfaces, has not been previously characterized. Piriform silk protein cDNAs were isolated from phage libraries of three species: A. trifasciata , N. clavipes , and N. cruentata . The deduced amino acid sequences from these genes revealed two new repetitive motifs: an alternating proline motif, where every other amino acid is proline, and a glutamine-rich motif of 6-8 amino acids. Similar to other spider silk proteins, the repeated segments are large (>200 amino acids) and highly homogenized within a species. There is also substantial sequence similarity across the genes from the three species, with particular conservation of the repetitive motifs. Northern blot analysis revealed that the mRNA is larger than 11 kb and is expressed exclusively in the piriform glands of the spider. Phylogenetic analysis of the C-terminal regions of the new proteins with published spidroins robustly shows that the piriform sequences form an ortholog group.
圆蛛织网的蛛丝纤维由非常大的、高度重复的蛋白质组装而成。这些重复片段依次包含短的、简单的和重复的氨基酸基序，这些基序决定了组装后纤维的物理和机械性能。在六种圆蛛丝纤蛋白中，形成附着盘的梨状丝此前尚未被表征，这种丝用于捆绑蛛网的关节并将拖丝附着在表面上。从三种蜘蛛（三带金蛛、棒络新妇蛛和红斑新妇蛛）的噬菌体文库中分离出了梨状丝蛋白的cDNA。从这些基因推导的氨基酸序列揭示了两个新的重复基序：一个交替脯氨酸基序，其中每隔一个氨基酸就是脯氨酸，以及一个由6 - 8个氨基酸组成的富含谷氨酰胺的基序。与其他蜘蛛丝蛋白类似，重复片段很大（>200个氨基酸），并且在一个物种内高度同质化。这三个物种的基因之间也存在显著的序列相似性，尤其是重复基序的保守性。Northern印迹分析表明，mRNA大于11 kb，且仅在蜘蛛的梨状腺中表达。用已发表的蛛丝蛋白对新蛋白质的C端区域进行系统发育分析，有力地表明梨状丝序列形成了一个直系同源组。
