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A conserved extended signal peptide region directs posttranslational protein translocation via a novel mechanism

Mickaël Desvaux^1,

¹ Division of Immunity and Infection, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
² Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115, USA
³ Center for Vaccine Development, University of Maryland, Baltimore, MD 21201, USA

Correspondence
Ian R. Henderson
I.R.Henderson{at}bham.ac.uk

Members of the type V secretion family are among the most prevalent secreted proteins in Gram-negative bacteria. A subset of this family, including Pet, the prototypical member of the Enterobacteriaceae serine proteases, possess unusual signal peptides which can be divided into five regions termed N1 (charged), H1 (hydrophobic), N2, H2 and C (cleavage site) domains. The N1 and H1 regions, which the authors have named the extended signal peptide region (ESPR), demonstrate remarkable conservation. In contrast, the N2, H2 and C regions show significant variability, and are reminiscent of typical Sec-dependent signal sequences. Despite several investigations, the function of the ESPR remains obscure. Here, it is shown that proteins possessing the ESPR are translocated in a posttranslational fashion. The presence of the ESPR severely impairs inner membrane translocation. Mutational analysis suggests that the ESPR delays inner membrane translocation by adopting a particular conformation, or by interacting with a cytoplasmic or inner membrane co-factor, prior to inner membrane translocation.

Present address: Institut National de la Recherche Agronomique (INRA), Centre de Recherche Clermont-Ferrand – Theix – Lyon, UR 454 – Unité de Microbiologie, Site de Theix, F-63122 Saint-Genès Champanelle, France.