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Spidroin is the main protein in a spider's dragline silk. It is part of a unique family of large structural proteins that make up the bulk of spider silk fibers. There are two types of spidroin: spidroin 1 and spidroin 2. They differ in their percentages of specific amino acids.〔Moisenovich M, Pustovalova O, Shackelford J, Vasiljeva T. Tissue regeneration in vivo within recombinant spidroin 1 scaffolds. Biomaterials 33 (2012) 3887e3898〕 Spidroin is part of a large group ofRH57H90307F proteins called scleroproteins. This group includes other structural proteins such as collagen and keratin. The specific characteristics of spidroins are becoming more commonly researched. A fiber of spidroin is as thick and resistant as one of steel but is more flexible. It can be stretched to approximately 135% of its original length without breaking. Its properties make it an excellent candidate for use in various scientific fields.〔Askarieh G, Hedhammar M, Nordling K, Saenz A, Casals C, Rising A, Johansson J & Knight S. Self-assembly of spider silk proteins is controlled by a pH-sensitive relay. Nature 465, 236–238 (13 May 2010) doi:10.1038/nature08962.〕 == Structure == Major ampullate spidroins are large proteins with an extension of 250-350 kDa, with an average of 3500 amino acids. They represent a polymeric organization, mostly based on highly homogenized tandem repeats. There are 100 tandem copies of 30 to 40 amino acids which repeat sequence and they represent more than 90% of the protein sequence.〔Xu M, Lewis RV. Structure of a protein superfiber: spider dragline silk. Proc Natl Acad Sci 1990, 87:7120-7124.http://www.pnas.org/content/87/18/7120.long〕 Alanine and glycine residues are the most abundant. Alanine appears in blocks of six to fourteen units that form β-sheets. These alanine blocks can stack to create crystalline structures in the fiber, linking different protein molecules together. Glycine is present in different motifs, such as GGX and GPGXX (where X = A, L, Q, or Y), that also have specific secondary structures (3 10 helix and β-spiral, respectively). Glycine-rich regions are more amorphous and contribute to extensibility and flexibility. Some of the differences observed between spidroin 1 and spidroin 2 (the most important major ampullate spidroins) are the proline content, which is very low in the first one but significant in the second one, and the motifs. Motif (GGX)n is characteristic in spidroin 1, while GPG and QQ are typical in spidroin 2. On the other hand, spidroins have non-repetitive amino (N) and carboxyl (C) terminal domains of approximately 150 and 100 amino acids respectively. N- and C-terminal domains share little resemblance, except that they are both rich in serine and both are largely amphipathic α-helical secondary structures. These domains are conserved not only between spidroin 1 and 2, but also among many silk types and spider species. Experimental data show the N- and C-terminal domains contribute to fiber assembly.〔Huemmerich D, Helsen CW, Quedzuweit S, Oschmann JRudolph R, Scheibel T: Primary structure elements of spider dragline silks and their contribution to protein solubility. Biochemistry 2004, 43:13604-13612. http://pubs.acs.org/doi/abs/10.1021/bi048983q〕 The C-terminal domain is involved in the organized transition from a soluble spidroin solution to an insoluble fiber during spinning.〔Sponner A, Vater W, Rommerskirch W, Vollrath F, Unger E, Grosse F, Weisshart K. The conserved C-termini contribute to the properties of spider silk fibroins. Biochem Biophys Res Commun. 2005b;338:897–902.http://www.ncbi.nlm.nih.gov/pubmed/16253207〕 In the N-terminal domain, there are signal peptides which regulate spidroin secretion from silk gland cells.〔Stark M, Grip S, Rising A, Hedhammar M, Engstrom W, Hjalm G, Johansson J. Macroscopic fibers self-assembled from recombinant miniature spider silk proteins. Biomacromolecules. 2007;8:1695–1701. http://www.ncbi.nlm.nih.gov/pubmed/17402782〕〔Garb J, Ayoub N, Hayashi C. Untangling spider silk evolution with spidroin terminal domains. BMC Evolutionary Biology. 2010, 10:243. http://www.biomedcentral.com/1471-2148/10/243〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spidroin」の詳細全文を読む スポンサード リンク
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