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Structure of the Bacillus cell fate determinant SpoIIAA in phosphorylated and unphosphorylated forms

Seavers, P.R., Lewis, R.J., Brannigan, J.A., Verschueren, K.H.J., Murshudov, G.N. and Wilkinson, A.J. (2001) Structure of the Bacillus cell fate determinant SpoIIAA in phosphorylated and unphosphorylated forms. Structure, 9 (7). pp. 605-614. ISSN 0969-2126

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Abstract

Background: The asymmetric cell division during sporulation in Bacillus subtilis gives rise to two compartments: the mother cell and the forespore. Each follow different programs of gene expression coordinated by a succession of alternate RNA polymerase σ factors. The activity of the first of these σ factors, σF, is restricted to the forespore although σF is present in the predivisional cell and partitions into both compartments following the asymmetric septation. For σF to become active, it must escape from a complex with its cognate anti-σ factor, SpoIIAB. This relief from SpoIIAB inhibition requires the dephosphorylation of the anti-σ factor antagonist, SpoIIAA. The phosphorylation state of SpoIIAA is thus a key determinant of σF activity and cell fate.

Results: We have solved the crystal structures of SpoIIAA from Bacillus sphaericus in its phosphorylated and unphosphorylated forms. The overall structure consists of a central β-pleated sheet, one face of which is buried by a pair of α helices, while the other is largely exposed to solvent. The site of phosphorylation, Ser57, is located at the N terminus of helix α2. The phosphoserine is exceptionally well defined in the 1.2 Å electron density maps, revealing that the structural changes accompanying phosphorylation are slight.

Conclusions: Comparison of unphosphorylated and phosphorylated SpoIIAA shows that covalent modification has no significant effect on the global structure of the protein. The phosphoryl group has a passive role as a negatively charged flag rather than the active role it plays as a nucleus of structural reorganization in many eukaryotic signaling systems.

Item Type: Article
Academic Units: The University of York > Chemistry (York)
Depositing User: York RAE Import
Date Deposited: 10 Feb 2009 15:16
Last Modified: 10 Feb 2009 15:16
Published Version: http://dx.doi.org/10.1016/S0969-2126(01)00623-2
Status: Published
Publisher: Elsevier
Identification Number: 10.1016/S0969-2126(01)00623-2
URI: http://eprints.whiterose.ac.uk/id/eprint/7578

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