Department of Biology, Laurentian University, Ramsey Lake Road, Sudbury, Ont., Canada P3E 2C6.
Microbiol Res. 2010;165(1):1-10. doi: 10.1016/j.micres.2008.03.002. Epub 2008 Apr 14.
Just as in the Eukarya and the Bacteria, members of the Archaea need to export proteins beyond the cell membrane. This would be required to fulfill a variety of essential functions such as nutrient acquisition and biotransformations, maintenance of extracellular structures and more. Apart from the Eukarya and the Bacteria however, members of the Archaea share a number of unique characteristics. Does this uniqueness extend to the protein secretion system? It was the objective of this study to answer this question. To overcome the limited experimental information on secreted proteins in Archaea, this study was carried out by subjecting the available archaeal genomes, which represent halophiles, thermophiles, and extreme thermophiles, to bioinformatics analysis. Specifically, to examine the properties of the secretomes of the Archaea using the ExProt program. A total of 24 genomes were analyzed. Secretomes were found to fall in the range of 6% of total ORFs (Methanopyrus kandleri) to 19% (Halobacterium sp. NRC-1). Methanosarcina acetivorans has the highest fraction of lipoproteins (at 89) and the lowest (at 1) were members of the Thermoplasma, Pyrobaculum aerophilum, and Nanoarchaeum equitans. Based on the Tat consensus sequence, contribution of these secreted proteins to the secretomes were negligible, making up 8 proteins out of a total of 7105 predicted exported proteins. Amino acid composition, an attribute of signal peptides not used as a selection criteria by ExProt, of predicted archaeal signal peptides show that in the haloarchaea secretomes, the frequency of the amino acid Lys is much lower than that seen in bacterial signal peptides, but is compensated for by a higher frequency of Arg. It also showed that higher frequencies for Thr, Val, and Gly contribute to the hydrophobic character in haloarchaeal signal peptides, unlike bacterial signal peptides in which the hydrophobic character is dominated by Leu and Ile.
正如真核生物和细菌一样，古菌的成员需要将蛋白质输出到细胞膜之外。这对于履行各种基本功能是必要的，例如营养物质的获取和生物转化、维持细胞外结构等。然而，除了真核生物和细菌之外，古菌的成员还具有许多独特的特征。这种独特性是否延伸到蛋白质分泌系统？本研究的目的是回答这个问题。为了克服古菌分泌蛋白实验信息有限的问题，本研究通过对现有的古菌基因组进行生物信息学分析，这些基因组代表了嗜盐菌、嗜热菌和极端嗜热菌。具体来说，使用 ExProt 程序检查古菌分泌组的特性。总共分析了 24 个基因组。发现分泌组的范围在总 ORF 的 6%（甲烷八叠球菌）到 19%（盐杆菌 NRC-1）之间。产甲烷乙酰杆菌的脂蛋白比例最高（为 89%），而嗜热原体、嗜热硫还原杆菌和 Nanoarchaeum equitans 的脂蛋白比例最低（为 1%）。根据 Tat 保守序列，这些分泌蛋白对分泌组的贡献可以忽略不计，在总共预测的 7105 个分泌蛋白中，只有 8 个是 Tat 信号肽。预测的古菌信号肽的氨基酸组成，这是 ExProt 未用作选择标准的信号肽属性，表明在盐杆菌分泌组中，Lys 氨基酸的频率远低于细菌信号肽，但被 Arg 更高的频率所补偿。它还表明，Thr、Val 和 Gly 的更高频率有助于盐杆菌信号肽的疏水性，而细菌信号肽的疏水性主要由 Leu 和 Ile 主导。
