Signal peptide hydrophobicity is critical for early stages in protein export by Bacillus subtilis.
Signal peptides that direct protein export in Bacillus subtilis are overall more hydrophobic than signal peptides in Escherichia coli. To study the importance of signal peptide hydrophobicity for protein export in both organisms, the alpha-amylase AmyQ was provided with leucine-rich (high hydrophobicity) or alanine-rich (low hydrophobicity) signal peptides. AmyQ export was most efficiently directed by the authentic signal peptide, both in E. coli and B. subtilis. The leucine-rich signal peptide directed AmyQ export less efficiently in both organisms, as judged from pulse-chase labelling experiments. Remarkably, the alanine-rich signal peptide was functional in protein translocation only in E. coli. Cross-linking of in vitro synthesized ribosome nascent chain complexes (RNCs) to cytoplasmic proteins showed that signal peptide hydrophobicity is a critical determinant for signal peptide binding to the Ffh component of the signal recognition particle (SRP) or to trigger factor, not only in E. coli, but also in B. subtilis. The results show that B. subtilis SRP can discriminate between signal peptides with relatively high hydrophobicities. Interestingly, the B. subtilis protein export machinery seems to be poorly adapted to handle alanine-rich signal peptides with a low hydrophobicity. Thus, signal peptide hydrophobicity appears to be more critical for the efficiency of early stages in protein export in B. subtilis than in E. coli.
Zanen
Geeske
G
Department of Pharmaceutical Biology, University of Groningen, the Netherlands.
Houben
Edith N G
EN
Meima
Rob
R
Tjalsma
Harold
H
Jongbloed
Jan D H
JD
Westers
Helga
H
Oudega
Bauke
B
Luirink
Joen
J
van Dijl
Jan Maarten
JM
Quax
Wim J
WJ
D000409:Alanine; D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D007930:Leucine; D019696:Peptidylprolyl Isomerase / Q000378:metabolism; D021382:Protein Sorting Signals; D021381:Protein Transport; D018271:Signal Recognition Particle / Q000378:metabolism; D000516:alpha-Amylases / Q000378:metabolism
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D021382:Protein Sorting Signals; D018271:Signal Recognition Particle; D000516:alpha-Amylases; C403324:trigger factor, E coli; D019696:Peptidylprolyl Isomerase; D007930:Leucine; D000409:Alanine