Streatfield, S.J. and Sandkvist, M. and Sixma, T.K. and Bagdasarian, M. and Hol, W.G.J. and Hirst, T.R. (1992) Intermolecular interactions between the a-subunit and b-subunit of heat-labile enterotoxin from escherichia-coli promote holotoxin assembly and stability invivo. Proceedings of the National Academy of Sciences of the United States of America, 89 (24). pp. 12140-12144. ISSN 0027-8424.
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Cholera toxin and the related heat-labile enterotoxin (LT) produced by Escherichia coli consist of a holotoxin of one A subunit and five B subunits (AB5). Here we investigate the domains of the A subunit (EtxA) of E. coli LT which influence the events of B-subunit (EtxB) oligomerization and the formation of a stable AB5 holotoxin complex. We show that the C-terminal 14 amino acids of the A subunit comprise two functional domains that differentially affect oligomerization and holotoxin stability. Deletion of the last 14 amino acids (-14) from the A subunit resulted in a molecule that was significantly impaired in its capacity to promote the assembly of a mutant B subunit, EtxB191.5. In contrast, deletion of the last four amino acids (-4) from the A subunit gave a molecule that retained such a capacity. This suggests that C-terminal residues within the -14 to -4 region of the A subunit are important for promoting the oligomerization of EtxB. In addition, we demonstrate that the truncated A subunit lacking the last 4 amino acids was unable to form a stable AB5 holotoxin complex even though it promoted B-subunit oligomerization. This suggests that the last 4 residues of the A subunit function as an "anchoring" sequence responsible for maintaining the stability of A/B subunit interaction during holotoxin assembly. These data represent an important example of how intermolecular interactions between polypeptides in vivo can modulate the folding and assembly of a macromolecular complex.
|Uncontrolled keywords:||protein export; protein folding; endoplasmic reticulum retention signal; cholera toxin|
|Divisions:||Faculties > Science Technology and Medical Studies > School of Biosciences|
|Depositing User:||O.O. Odanye|
|Date Deposited:||31 Aug 2009 21:47|
|Last Modified:||31 Aug 2009 21:47|
|Resource URI:||http://kar.kent.ac.uk/id/eprint/22247 (The current URI for this page, for reference purposes)|
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