Pollitt S, Inouye S, Inouye M
J Biol Chem. 1986 Feb 5;261(4):1835-7.
The requirement for the glycine residue at the COOH terminus of the signal peptide of the precursor of the major Escherichia coli outer membrane lipoprotein was examined. Using oligonucleotide-directed site-specific mutagenesis, this residue was replaced by residues of increasing side chain size. Substitution by serine had no effect on the modification or processing of the prolipoprotein. Substitution by valine or leucine resulted in the accumulation of the unmodified precursor, whereas threonine substitution resulted in slow lipid modification and no detectable processing of the lipid modified precursor. The results indicate that serine is the upper limit on size for the residue at the cleavage site. Larger residues at this position prevent the action of both the glyceride transferase and signal peptidase II enzymes, indicating that the cleavage site residue plays a role in events prior to proteolytic cleavage. The upper limit on size of the cleavage site residue is similar to that found for exported proteins cleaved by signal peptidase I, as well as eucaryotic exported proteins. The possibility that the cleavage site residue may have a role other than active site recognition by the signal peptidase is discussed.
对大肠杆菌主要外膜脂蛋白前体信号肽COOH末端甘氨酸残基的需求进行了研究。利用寡核苷酸定向位点特异性诱变，将该残基替换为侧链尺寸不断增加的残基。用丝氨酸替代对前脂蛋白的修饰或加工没有影响。用缬氨酸或亮氨酸替代导致未修饰前体的积累，而苏氨酸替代导致脂质修饰缓慢且未检测到脂质修饰前体的加工。结果表明，丝氨酸是切割位点残基大小的上限。该位置较大的残基会阻止甘油酯转移酶和信号肽酶II的作用，表明切割位点残基在蛋白水解切割之前的事件中起作用。切割位点残基大小的上限与信号肽酶I切割的输出蛋白以及真核输出蛋白的上限相似。还讨论了切割位点残基可能具有信号肽酶活性位点识别以外其他作用的可能性。
