Gowda K, Black S D, Moeller I, Sakakibara Y, Liu M C, Zwieb C
Department of Molecular Biology, University of Texas Health Science Center at Tyler 75710, USA.
Gene. 1998 Jan 30;207(2):197-207. doi: 10.1016/s0378-1119(97)00627-6.
Signal recognition particle (SRP) plays a critical role in the targeting of secretory proteins to cellular membranes. An essential component of SRP is the protein SRP54, which interacts not only with the nascent signal peptide, but also with the SRP RNA. To understand better how protein targeting occurs in the human system, the human SRP54 gene was cloned, sequenced, and the protein was expressed in bacteria and insect cells. Recombinant SRP54 was purified from both sources. The protein bound to SRP RNA in the presence of protein SRP19, and associated with the signal peptide of in vitro translated pre-prolactin. Comparative sequence analysis of human SRP54 with homologs from all three phylogenetic domains was combined with high-stringency protein secondary structure prediction. A conserved RNA-binding loop was predicted in the largely helical M-domain of SRP54. Contrary to general belief, the unusually high number of methionine residues clustered outside the predicted helices, thus indicating a mechanism of signal peptide recognition that may involve methionine-rich loops.
信号识别颗粒（SRP）在分泌蛋白靶向细胞膜的过程中起着关键作用。SRP的一个重要组成部分是蛋白质SRP54，它不仅与新生信号肽相互作用，还与SRP RNA相互作用。为了更好地理解人类系统中蛋白质靶向是如何发生的，人类SRP54基因被克隆、测序，并在细菌和昆虫细胞中表达该蛋白质。重组SRP54从这两种来源中纯化出来。该蛋白质在蛋白质SRP19存在的情况下与SRP RNA结合，并与体外翻译的前催乳素的信号肽相关联。将人类SRP54与来自所有三个系统发育域的同源物进行比较序列分析，并结合高严格度的蛋白质二级结构预测。在SRP54的主要为螺旋结构的M结构域中预测到一个保守的RNA结合环。与一般看法相反，异常大量的甲硫氨酸残基聚集在预测螺旋之外，因此表明信号肽识别机制可能涉及富含甲硫氨酸的环。
