SecDF of Bacillus subtilis, a molecular Siamese twin required for the efficient secretion of proteins.
In the present studies, we show that the SecD and SecF equivalents of the Gram-positive bacterium Bacillus subtilis are jointly present in one polypeptide, denoted SecDF, that is required to maintain a high capacity for protein secretion. Unlike the SecD subunit of the pre-protein translocase of Escherichia coli, SecDF of B. subtilis was not required for the release of a mature secretory protein from the membrane, indicating that SecDF is involved in earlier translocation steps. Strains lacking intact SecDF showed a cold-sensitive phenotype, which was exacerbated by high level production of secretory proteins, indicating that protein translocation in B. subtilis is intrinsically cold-sensitive. Comparison with SecD and SecF proteins from other organisms revealed the presence of 10 conserved regions in SecDF, some of which appear to be important for SecDF function. Interestingly, the SecDF protein of B. subtilis has 12 putative transmembrane domains. Thus, SecDF does not only show sequence similarity but also structural similarity to secondary solute transporters. Our data suggest that SecDF of B. subtilis represents a novel type of the SecD and SecF proteins, which seems to be present in at least two other organisms.
Department of Genetics, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.
A
A
Bolhuis
C P
CP
Broekhuizen
A
A
Sorokin
M L
ML
van Roosmalen
G
G
Venema
S
S
Bron
W J
WJ
Quax
J M
JM
van Dijl
D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C499394:SecD protein, E coli; C489583:SecF protein, E coli; C075767:secD protein, Bacteria; C075768:secF protein, Bacteria