Conservation of components of the export machinery in prokaryotes

Decook, H; Tommassen, Jan

doi:10.1016/0378-1097(91)90594-z

Cited by 17 publications

(17 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We also showed that S. marcescens SecB crossreacted strongly with E. coli SecB (see Fig. 2C), as reported previously (9). S. marcescens strain from which secB was deleted had defective pre-MBP processing.…”

Section: S Marcescenssupporting

confidence: 90%

“…A SecB homolog has been identified in S. marcescens on the basis of cross-reaction of a particular species with anti-E. coli SecB antibodies (9). Conversely, the specificity of the SecB chaperone for the Sec translocation system, especially the specific interaction with SecA (14), the ATPase of the Sec translocation system, make the involvement of SecB in type I secretion all the more puzzling.…”

mentioning

confidence: 99%

See 1 more Smart Citation

The SecB Chaperone Is Bifunctional in Serratia marcescens : SecB Is Involved in the Sec Pathway and Required for HasA Secretion by the ABC Transporter

2003

View full text Add to dashboard Cite

HasA is the secreted hemophore of the heme acquisition system (Has) of Serratia marcescens. It is secreted by a specific ABC transporter apparatus composed of three proteins: HasD, an inner membrane ABC protein; HasE, another inner membrane protein; and HasF, a TolC homolog. Except for HasF, the structural genes of the Has system are encoded by an iron-regulated operon. In previous studies, this secretion system has been reconstituted in Escherichia coli, where it requires the presence of the SecB chaperone, the Sec pathwaydedicated chaperone. We cloned and inactivated the secB gene from S. marcescens. We show that S. marcescens SecB is 93% identical to E. coli SecB and complements the secretion defects of a secB mutant of E. coli for both the Sec and ABC pathways of HasA secretion. In S. marcescens, SecB inactivation affects translocation by the Sec pathway and abolishes HasA secretion. This demonstrates that S. marcescens SecB is the genuine chaperone for HasA secretion in S. marcescens. These results also demonstrate that S. marcescens SecB is bifunctional, as it is involved in two separate secretion pathways. We investigated the effects of secB point mutations in the reconstituted HasA secretion pathway by comparing the translocation of a Sec substrate in various mutants. Two different patterns of SecB residue effects were observed, suggesting that SecB functions may differ for the Sec and ABC pathways.The type I secretion pathway (or ATP-binding cassette [ABC] pathway) is one of several pathways used by gramnegative bacteria to secrete proteins into the extracellular medium. It is widespread and is used for the secretion of proteins with various functions (3). It involves a secretion apparatus composed of three proteins: the ABC protein; the so-called membrane fusion protein in the cytoplasmic membrane, and a specific outer membrane protein of the TolC class, which creates a channel about 30 Å in diameter through the periplasmic space and the outer membrane (17) through which the secreted protein is most likely translocated.The type I secretion pathway presents several characteristic features. Secretion occurs in a single step, directly from the cytoplasm to the extracellular medium. The secretion signal is in most cases located at the C-terminal end of the secreted protein and is not cleaved during secretion. As a consequence, the secreted protein is entirely synthesized before secretion. The secretion apparatus assembles on demand, in response to a signal triggered by the association of this secretion signal with the ABC component of the secretion machinery (22, 36). The size of the proteins secreted by the type I pathway ranges from 50 to more than 4,000 amino acids. However, given the size of the channel created by the outer membrane component, this channel can only accommodate globular proteins of at most 150 to 200 amino acids, imposing strict constraints on the secretion process. We have recently shown that a folded ABC substrate cannot be translocated through the ABC secretion apparatus (8).HasA is ...

show abstract

Section: S Marcescenssupporting

confidence: 90%

mentioning

confidence: 99%

The SecB Chaperone Is Bifunctional in Serratia marcescens : SecB Is Involved in the Sec Pathway and Required for HasA Secretion by the ABC Transporter

2003

View full text Add to dashboard Cite

show abstract

“…These alleles, prlD21, -22, and -23 and azi-17, confer azide resistance, are potent enough with LamB17D-LacZ to allow SDI, and cause defects in the secretion of wild-type proteins. Strikingly, all alter Tyr-134, a residue conserved in all known SecA proteins (5,14,34,35,39,46,47,59,62). We suspect that these four mutations may slow an ATPase activity of SecA.…”

Section: Discussionmentioning

confidence: 92%

“…This discovery, together with the universal presence of signal sequences in secreted proteins, argues that the basic mechanism of protein secretion has been conserved throughout nature. While homologs of SecA have been found in other bacteria, in plastids of algae, and in chloroplasts of plants (5,14,34,35,39,46,47,59,62), none has been discovered in yeasts or mammals. Whether this reflects an important difference between prokaryotes and eukaryotes remains to be determined.…”

mentioning

confidence: 99%

Suppression of signal sequence defects and azide resistance in Escherichia coli commonly result from the same mutations in secA

Huie

Silhavy

1995

J Bacteriol

View full text Add to dashboard Cite

The SecA protein of Escherichia coli is required for protein translocation from the cytoplasm. The complexity of SecA function is reflected by missense mutations in the secA gene that confer several different phenotypes: (i) conditional-lethal alleles cause a generalized block in protein secretion, resulting in the cytoplasmic accumulation of the precursor forms of secreted proteins; (ii) azi alleles confer resistance to azide at concentrations up to 4 mM; and (iii) prlD alleles suppress a number of signal sequence mutations in several different genes. To gain further insights into the role of SecA in protein secretion, we have isolated and characterized a large number of prlD mutations, reasoning that these mutations alter a normal function of wild-type SecA. Our results reveal a striking coincidence of signal sequence suppression and azide resistance: the majority of prlD alleles also confer azide resistance, and all azi alleles tested are suppressors. We suggest that this correlation reflects the mechanism(s) of signal sequence suppression. There are two particularly interesting subclasses of prlD and azi alleles. First, four of the prlD and azi alleles exhibit special properties: (i) as suppressors they are potent enough to allow PrlD (SecA) inactivation by a toxic LacZ fusion protein marked with a signal sequence mutation (suppressor-directed inactivation), (ii) they confer azide resistance, and (iii) they cause modest defects in the secretion of wild-type proteins. Sequence analysis reveals that all four of these alleles alter Tyr-134 in SecA, changing it to Ser, Cys, or Asn. The second subclass consists of seven prlD alleles that confer azide supersensitivity, and sequence analysis reveals that six of these alleles are changes of Ala-507 to Val. Both of the affected amino acids are located within different putative ATP-binding regions of SecA and thus may affect ATPase activities of SecA. We suggest that the four azide-resistant mutations slow an ATPase activity of SecA, thus allowing successful translocation of increased amounts of mutant precursor proteins.

show abstract

“…Further (42). The existence of a Sec-like system in shigellae is suggested by the finding that polyclonal antisera to E. coli SecA and SecB recognize proteins of similar molecular masses in whole-cell protein extracts of S. flexneri and S. dysenteriae (18).…”

Section: Resultsmentioning

confidence: 99%

Unipolar localization and ATPase activity of IcsA, a Shigella flexneri protein involved in intracellular movement

et al. 1993

View full text Add to dashboard Cite

Shigella flexneri uses elements of the host cell cytoskeleton to move within cells and from cell to cell. IcsA, an S. flexneri protein involved in this movement, was purified and studied in vitro. IcsA bound the radiolabelled ATP analog 3'(2')-O-(4-benzoyl)benzoyl-ATP and hydrolyzed ATP. In addition, the surface localization of IcsA on both extracellular and intracellular shigellae was unipolar. Further, in HeLa cells infected with shigellae, IcsA antiserum labelled the actin tail throughout its length, thereby suggesting that IcsA interacts with elements within the tail. Localization of IcsA within the tail at a distance from the bacterium would require its secretion; we demonstrate here that in vitro IcsA is secreted into the culture supernatant in a cleaved form.

show abstract

Conservation of components of the export machinery in prokaryotes

Cited by 17 publications

References 12 publications

The SecB Chaperone Is Bifunctional in Serratia marcescens : SecB Is Involved in the Sec Pathway and Required for HasA Secretion by the ABC Transporter

The SecB Chaperone Is Bifunctional in Serratia marcescens : SecB Is Involved in the Sec Pathway and Required for HasA Secretion by the ABC Transporter

Suppression of signal sequence defects and azide resistance in Escherichia coli commonly result from the same mutations in secA

Unipolar localization and ATPase activity of IcsA, a Shigella flexneri protein involved in intracellular movement

Contact Info

Product

Resources

About