Weisman L S, Krummel B M, Wilson A C
J Biol Chem. 1986 Feb 15;261(5):2309-13.
Sequences are presented for the signal peptides of prelysozymes from 6 species of birds and compared to the known sequence for chicken prelysozyme c. The sequencing was done with synthetic oligonucleotides as primers and oviduct mRNA as the template, obviating the need to clone DNA from these species. Ring-necked pheasant prelysozyme c differs from all other prelysozymes c and pre-alpha-lactalbumins examined by being cleaved in vivo between amino acid residues 17 and 18 instead of between residues 18 and 19. The feature unique to the signal peptide of pheasant prelysozyme c is proline at position 17. Besides showing that proline is acceptable as the carboxyl-terminal amino acid of the signal peptide, our finding implies that it cannot occur as the penultimate amino acid in the signal peptide. This supports the view that unless a polypeptide has the proper secondary structure, signal peptidase will not cleave it, and that this secondary structure is a beta-turn. Another outcome of this comparative study is an estimate that the mean rate of sequence evolution in the prelysozyme signal peptide is 1%/two million years of divergence, similar to that calculated for the insulin signal peptide. Because this rate is a third of the silent substitution rate, it is likely that one out of every three amino acid substitutions is compatible with signal peptide function.
本文给出了6种鸟类前溶菌酶信号肽的序列，并与鸡前溶菌酶c的已知序列进行了比较。测序以合成寡核苷酸为引物，输卵管mRNA为模板，无需从这些物种中克隆DNA。环颈雉前溶菌酶c与所有其他已检测的前溶菌酶c和前α-乳白蛋白不同，它在体内是在氨基酸残基17和18之间而不是在残基18和19之间被切割。雉鸡前溶菌酶c信号肽的独特特征是第17位为脯氨酸。我们的发现不仅表明脯氨酸作为信号肽的羧基末端氨基酸是可以接受的，还意味着它不能作为信号肽的倒数第二个氨基酸出现。这支持了这样一种观点，即除非多肽具有适当的二级结构，信号肽酶不会切割它，并且这种二级结构是一个β-转角。这项比较研究的另一个结果是估计前溶菌酶信号肽的序列进化平均速率为每分化两百万年1%，与胰岛素信号肽的计算速率相似。由于这个速率是沉默替代速率的三分之一，每三个氨基酸替代中可能有一个与信号肽功能兼容。
