Conformation of protein secreted across bacterial outer membranes: a study of enterotoxin translocation from Vibrio cholerae

Journal Article · Sat Oct 31 23:00:00 EST 1987 · Proc. Natl. Acad. Sci. U.S.A.; (United States)

DOI:https://doi.org/10.1073/pnas.84.21.7418· OSTI ID:6837894

Hirst, T R; Holmgren, J

The secretion of enterotoxin by Vibrio cholerae is punctuated by the transient entry of the toxin subunits into the periplasm. In this paper, the authors show that the subunits oligomerize into an assembled holotoxin within the periplasm prior to their secretion across the outer membrane. The rate of toxin assembly was studied by pulse-labeling cells with (/sup 35/S)-methionine and then monitoring the turnover of radiolabeled subunits as they assembled within the periplasm. The subunits entered the periplasm as monomers and assembled into oligomers with a half-time of approx. = 1 min. Since assembly was a rapid event compared to the rate of toxin efflux from the periplasm, which had a half-time of approx. = 13 min, they conclude that all of the subunits that pass through the periplasm assemble before they traverse the outer membrane. The average concentration of subunit monomers and assembled holotoxin within the periplasm was calculated to be approx. = 20 and approx. = 260 ..mu..g/ml, respectively. This indicates that the periplasm is a suitably concentrated milieu where spontaneous toxin assembly can occur. These findings suggest that protein movement across bacterial outer membranes, in apparent contrast to export across other biological membranes, involves translocation of polypeptides that have already folded into tertiary and even quaternary conformations.

• Research Organization: Univ. of Leicester (England)
• OSTI ID: 6837894
• Journal Information: Proc. Natl. Acad. Sci. U.S.A.; (United States), Journal Name: Proc. Natl. Acad. Sci. U.S.A.; (United States) Vol. 84:21; ISSN PNASA
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
ANTIGENS
AUTORADIOGRAPHY
BACTERIA
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CELL MEMBRANES
DAYS LIVING RADIOISOTOPES
DRUGS
ELECTROPHORESIS
ENZYME IMMUNOASSAY
EVEN-ODD NUCLEI
IMMUNOASSAY
ISOTOPES
LIGHT NUCLEI
LIPOTROPIC FACTORS
MATERIALS
MEMBRANE TRANSPORT
MEMBRANES
METHIONINE
MICROORGANISMS
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
PEPTIDES
PROTEINS
RADIOISOTOPES
SECRETION
SULFUR 35
SULFUR ISOTOPES
TOXIC MATERIALS
TOXINS