Signal Peptide Peptidase- and ClpP-like Proteins of Bacillus subtilis Required for Efficient Translocation and Processing of Secretory Proteins

Abstract

Signal peptides direct the export of secretory proteins from the cytoplasm. After processing by signal peptidase, they are degraded in the membrane and cytoplasm. The resulting fragments can have signaling functions. These observations suggest important roles for signal peptide peptidases. The present studies show that the Gram-positive eubacterium Bacillus subtilis contains two genes for proteins, denoted SppA and TepA, with similarity to the signal peptide peptidase A of Escherichia coli. Notably, TepA also shows similarity to ClpP proteases. SppA of B. subtilis was only required for efficient processing of pre-proteins under conditions of hyper-secretion. In contrast, TepA depletion had a strong effect on pre-protein translocation across the membrane and subsequent processing, not only under conditions of hyper-secretion. Unlike SppA, which is a typical membrane protein, TepA appears to have a cytosolic localization, which is consistent with the observation that TepA is involved in early stages of the secretion process. Our observations demonstrate that SppA and TepA have a role in protein secretion in B. subtilis. Based on their similarity to known proteases, it seems likely that SppA and TepA are specifically required for the degradation of proteins or (signal) peptides that are inhibitory to protein translocation.

Dissecting virulence pathways of Mycobacterium tuberculosis through protein–protein association

“…Because FtsQ has been shown to interact with components of SecYEG translocon (25), it is possible that FtsQ participates in the delivery of Cfp-10 to the SecYEG translocon. Furthermore, we detected a positive interaction between Cfp-10 and the AAA-ATPase chaperone ClpC1 (a member of the Clp͞Hsp100 family of proteins), which are involved in diverse functions, including secretion, gene regulation, protein refolding, and degradation (26,27) and have been shown to associate with the translocation machinery in the chloroplast membrane (28). It may well be that Mtb ClpC1 facilitates Cfp-10 secretion by associating with the translocation complex in the membrane.…”

The Bacillus subtilis ABC transporter EcsAB influences intramembrane proteolysis through RasP

“…Both, SppA and YqeZ are s W -controlled (Huang et al, 1999;Wiegert et al, 2001), and for YqeZ a function for immunity against sublancin rather than degradation of signal peptides has been shown (Butcher & Helmann, 2006). For SppA (YteI) and TepA (YmfB), a function in degradation of proteins or (signal) peptides that are inhibitory to protein translocation has been proposed (Bolhuis et al, 1999). Signal peptide peptidases described for eukaryotes belong to the group of intramembrane cleaving proteases, and attack certain signal peptides after they have been clipped from newly synthesized secretory or membrane proteins (Weihofen & Martoglio, 2003).…”

“…E. coli SppA (protease IV) has been shown to degrade the processed signal sequence of the major lipoprotein, but it is not the only protease that is responsible for signal peptide digestion in the cell envelope (Suzuki et al, 1987). For B. subtilis, three proteins similar to SppA have been described (TepA, SppA and YqeZ; Bolhuis et al, 1999;Helmann, 2002). Both, SppA and YqeZ are s W -controlled (Huang et al, 1999;Wiegert et al, 2001), and for YqeZ a function for immunity against sublancin rather than degradation of signal peptides has been shown (Butcher & Helmann, 2006).…”

Identification of Bacillus subtilis σW‐dependent genes that provide intrinsic resistance to antimicrobial compounds produced by Bacilli

“…Exceptions include the fosB fosfomycin-resistance gene (Cao et al, 2001), the pbpE penicillin-binding protein (Popham and Setlow, 1993), and sppA which may play a role in degradation of cleaved signal peptides (Bolhuis et al, 1999). Bioinformatic analysis suggests that several other σ W -dependent operons may function in bacteriocin or antibiotic resistance (Cao et al, 2002b).…”