The Stable Interaction Between Signal-Peptidase LepB of Escherichia coli and Nuclease Bacteriocins Promotes Toxin Entry into the Cytoplasm [Microbiology]

October 23rd, 2015 by Mora, L., Moncoq, K., England, P., Oberto, J., de Zamaroczy, M.

LepB is a key membrane component of the cellular secretion machinery, which releases secreted proteins into the periplasm by cleaving the inner membrane-bound leader. We showed that LepB is also an essential component of the machinery hijacked by the tRNase colicin D for its import. Here we demonstrate that this non-catalytic activity of LepB is to promote the association of the central domain of colicin D with the inner membrane, prior to the FtsH-dependent proteolytic processing and translocation of the toxic tRNase domain into the cytoplasm. The novel structural role of LepB results in a stable interaction with colicin D, with a stoichiometry of 1:1 and a nanomolar Kd determined in vitro. LepB provides a chaperone-like function for the penetration of several nuclease-type bacteriocins into target cells. The colicin-LepB interaction is shown to require only a short peptide sequence within the central domain of these bacteriocins and to involve residues present in the short C-terminal Box E of LepB. Genomic screening identified the conserved LepB binding motif in colicin-like ORFs from thirteen additional bacterial species. These findings establish a new paradigm for the functional adaptability of an essential inner-membrane enzyme.
  • Posted in Journal of Biological Chemistry, Publications
  • Comments Off on The Stable Interaction Between Signal-Peptidase LepB of Escherichia coli and Nuclease Bacteriocins Promotes Toxin Entry into the Cytoplasm [Microbiology]