514 publications from this institution
Signal peptidases remove targeting peptides from pre-proteins and play central roles in the secretory pathway, as well as in the delivery of proteins to the mitochondrial intermembrane space and to the lumen of thylakoids. The catalytic mechanism of pre-protein cleavage has long been an enigma, but recent data from site-directed mutageneis and sequence alignment studies suggest that signal peptidases may constitute a new type of serine protease, mechanistically related to the β-lactamases.
We have shown previously that the 100-residue-long periplasmic N-terminal tail of the <i>Escherichia coli</i> inner membrane protein ProW can be translocated across the inner membrane in a <i>sec</i>-independent manner and that its translocation is blocked by the introduction of three positively charged residues near its C-terminal end (Whitley, P., Zander, T., Ehrmann, M., Haardt, M., Bremer, E., and von Heijne, G.(1994) <i>EMBO J.</i> 13, 4653-4661). We have now further analyzed the requirements for translocation of the N-terminal tail and found that the introduction of even a single arginine can block translocation. Position-specific differences in the effects on translocation of arginine insertions suggest that the C-terminal end of the N-terminal tail is more critical for translocation than the central and N-terminal regions. We also show that the N-terminal tail is translocated in a truncation mutant where a stop codon is placed immediately after the first transmembrane segment, provided that the transmembrane segment is flanked on its C-terminal end by positively charged residues. Thus, <i>sec</i>-independent translocation of a relatively large domain can be induced by a translocation signal located at the extreme C terminus of a protein.
