Role of the propilin leader peptide in the maturation of F pilin.
F-pilin maturation and translocation result in the cleavage of a 51-amino-acid leader sequence from propilin and require LepB and TraQ but not the SecA-SecY secretion pathway. The unusual propilin leader peptide and the dependence of its cleavage on TraQ suggested that TraQ recognition may be specific for the leader peptide. An in vitro propilin cleavage assay yielded propilin (13 kDa), the pilin polypeptide (7 kDa), and a 5.5-kDa protein as the traA products. The 5.5-kDa protein comigrates with the full-length 51-amino-acid leader peptide, and [14C]proline labeling confirmed its identity since the only proline residues of propilin are found within the leader peptide. The in vitro and in vivo propilin-processing reactions proceed similarly in a single polypeptide cleavage step. Furthermore, TraQ dependence is a property of F-pilin maturation specifically rather than a property of the leader peptide. A propilin derivative with an amino-terminal signal sequence generated by deleting codons 2 to 28 required TraQ for processing in vivo. On the other hand, a chimeric protein with the propilin wild-type leader peptide fused to the mature portion of beta-lactamase was processed in a TraQ-independent manner. Thus, despite its unusual length, the propilin leader peptide seems to perform a function similar to that of the typical amino-terminal signal sequence. This work suggests that TraQ is not necessary for the proteolysis of propilin and therefore is likely to act as a chaperone-like protein that promotes the translocation of propilin.
Majdalani
N
N
Department of Medical Microbiology and Immunology, Texas A&M University Health Science Center, College Station, Texas 77843. USA.
Moore
D
D
Maneewannakul
S
S
Ippen-Ihler
K
K
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D029968:Escherichia coli Proteins; D036781:Fimbriae Proteins; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D017931:DNA Primers; D029968:Escherichia coli Proteins; C444040:F pilin, E coli; D008565:Membrane Proteins; D010455:Peptides; D011498:Protein Precursors; D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D036781:Fimbriae Proteins