Gascuel O, Danchin A
J Mol Evol. 1986;24(1-2):130-42. doi: 10.1007/BF02099961.
Investigation of possible variations between prokaryotic and eukaryotic signal sequences of exported proteins has revealed unexpected differences. Apart from the known similarities (presence of a core hydrophobic sequence preceded by a positively charged amino terminus and followed by a flexible structure), we have found that the core is much more rigid in eukaryotic signals than in their prokaryotic counterparts, and that at both ends the constraints are much more stringent in bacteria than in human cells. The differences have been summarized as a set of 17 criteria describing noteworthy features discriminating between the two classes of signal peptides. The program we used permitted each class of sequences to be learned; Escherichia coli sequences were well learned (i.e., they could be recognized by the programs as having common features), whereas human sequences were found to exhibit a much wider variation. Thus it was possible to propose a consensus in the case of the bacterial peptides, but none (or a much looser one) in the case of the human sequences. Two sequences were exceptional among the E. coli signal peptides, those of lipoprotein and plasmid-borne beta-lactamase, suggesting that they have special origins or destinations. Finally, the differences found strongly suggest that the mode of secretion is rather different in the two types of organisms, in spite of the common features of the signal sequences.
对输出蛋白的原核和真核信号序列之间可能存在的差异进行研究后，发现了一些意外的不同之处。除了已知的相似之处（存在一个核心疏水序列，其前面是带正电荷的氨基末端，后面是一个柔性结构），我们还发现，真核信号中的核心比其原核对应物更具刚性，而且在两端，细菌中的限制比人类细胞中的更为严格。这些差异已归纳为一组17条标准，描述了区分这两类信号肽的显著特征。我们使用的程序允许学习每一类序列；大肠杆菌序列能够很好地被学习（即它们能够被程序识别为具有共同特征），而人类序列则表现出更大的变异性。因此，对于细菌肽，可以提出一个共有序列，但对于人类序列则无法提出（或只能提出一个宽松得多的共有序列）。在大肠杆菌信号肽中，脂蛋白和质粒携带的β-内酰胺酶的两个序列是例外，这表明它们有特殊的起源或去向。最后，尽管信号序列有共同特征，但所发现的差异强烈表明，这两种生物体的分泌方式相当不同。
