A. Van Dalen et al., Delta psi stimulates membrane translocation of the C-terminal part of a signal sequence, J BIOL CHEM, 274(28), 1999, pp. 19913-19918
For several proteins in Escherichia coli it has been shown that the protonm
otive force (pmf) dependence of translocation can be varied with the signal
sequence composition, suggesting an effect of the pmf on the signal sequen
ce. To test this possibility, we analyzed the effect of the membrane potent
ial on translocation of the signal sequence. For this purpose, a precursor
peptide was used (SP+7), corresponding to the signal sequence of PhoE with
the first seven amino acids of the mature part that can be processed by pur
ified leader peptidase, Translocation was studied in pure lipid vesicles co
ntaining leader peptidase, with its active site inside the vesicles. In the
presence of a positive inside Delta Psi the amount of processing of SP+7 w
as significantly higher than without a Delta Psi, indicating that the trans
location of the cleavage region is stimulated by Delta Psi. Replacement of
the helix-breaking glycine residue at position -10 in the signal sequence f
or a leucine abolished the effect of Delta Psi on the translocation of the
cleavage region. It is concluded that Delta Psi directly acts on the wild t
ype signal sequence by stimulating the translocation of its C terminus. We
propose that Delta Psi acts on the signal sequence by stretching it into a
transmembrane orientation.