Shcherban T Y, Shi J, Durachko D M, Guiltinan M J, McQueen-Mason S J, Shieh M, Cosgrove D J
Department of Biology, Pennsylvania State University, University Park 16802, USA.
Proc Natl Acad Sci U S A. 1995 Sep 26;92(20):9245-9. doi: 10.1073/pnas.92.20.9245.
Expansins are unusual proteins discovered by virtue of their ability to mediate cell wall extension in plants. We identified cDNA clones for two cucumber expansins on the basis of peptide sequences of proteins purified from cucumber hypocotyls. The expansin cDNAs encode related proteins with signal peptides predicted to direct protein secretion to the cell wall. Northern blot analysis showed moderate transcript abundance in the growing region of the hypocotyl and no detectable transcripts in the nongrowing region. Rice and Arabidopsis expansin cDNAs were identified from collections of anonymous cDNAs (expressed sequence tags). Sequence comparisons indicate at least four distinct expansin cDNAs in rice and at least six in Arabidopsis. Expansins are highly conserved in size and sequence (60-87% amino acid sequence identity and 75-95% similarity between any pairwise comparison), and phylogenetic trees indicate that this multigene family formed before the evolutionary divergence of monocotyledons and dicotyledons. Sequence and motif analyses show no similarities to known functional domains that might account for expansin action on wall extension. A series of highly conserved tryptophans may function in expansin binding to cellulose or other glycans. The high conservation of this multigene family indicates that the mechanism by which expansins promote wall extensin tolerates little variation in protein structure.
扩展蛋白是一类特殊的蛋白质，因其能够介导植物细胞壁伸展而被发现。我们根据从黄瓜下胚轴中纯化的蛋白质的肽序列，鉴定出了两个黄瓜扩展蛋白的cDNA克隆。这些扩展蛋白cDNA编码的相关蛋白质带有预测可将蛋白质分泌到细胞壁的信号肽。Northern印迹分析表明，下胚轴生长区域的转录本丰度适中，而在非生长区域未检测到转录本。从匿名cDNA（表达序列标签）文库中鉴定出了水稻和拟南芥的扩展蛋白cDNA。序列比较表明，水稻中至少有四个不同的扩展蛋白cDNA，拟南芥中至少有六个。扩展蛋白在大小和序列上高度保守（任何两两比较之间的氨基酸序列同一性为60 - 87%，相似性为75 - 95%），系统发育树表明，这个多基因家族在单子叶植物和双子叶植物进化分化之前就已形成。序列和基序分析表明，与可能解释扩展蛋白对细胞壁伸展作用的已知功能域没有相似性。一系列高度保守的色氨酸可能在扩展蛋白与纤维素或其他聚糖的结合中起作用。这个多基因家族的高度保守表明，扩展蛋白促进细胞壁伸展的机制在蛋白质结构上几乎没有变化。
