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Journal of Bacteriology, December 2008, p. 8009-8017, Vol. 190, No. 24
0021-9193/08/$08.00+0     doi:10.1128/JB.01073-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Amino Acid Substitutions in Transmembrane Domains 9 and 10 of GerVB That Affect the Germination Properties of Bacillus megaterium Spores{triangledown}

Graham Christie* and Christopher R. Lowe

Institute of Biotechnology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QT, United Kingdom

Received 1 August 2008/ Accepted 7 October 2008

The molecular basis for differences in germinant recognition of Bacillus megaterium QM B1551 spores containing the GerVB and/or GerUB receptor proteins has been examined by site-directed mutagenesis and the construction of cross-homologue chimeras. Focusing on nonconserved residues predicted to reside in transmembrane domains 9 and 10, we demonstrate that GerVB residues Ser319 and Leu345 are of particular importance in defining the specificity and apparent affinity of the receptor for germinants. Kinetic analyses of mutants with different amino acid substitutions at these positions indicate that Ser319 and Leu345 are not involved directly in the binding of germinants, but probably reside in regions of the receptor where structural perturbations can affect the conformation of, or access to, germinant binding sites. Position 345 is also shown to be of importance in GerUB, where the F345A mutation severely impairs receptor function. Functionality is restored in the GerUB Ala345 background by substituting putative outer-loop residues adjacent to TM10 for the corresponding residues in GerVB, indicating that a degree of structural coordination between these regions is important to receptor function.

* Corresponding author. Mailing address: Institute of Biotechnology, University of Cambridge, Tennis Court Road, Cambridge, United Kingdom CB2 1QT. Phone: 01223 764959. Fax: 01223 334162. E-mail: gc301{at}cam.ac.uk

{triangledown} Published ahead of print on 17 October 2008.

Journal of Bacteriology, December 2008, p. 8009-8017, Vol. 190, No. 24
0021-9193/08/$08.00+0     doi:10.1128/JB.01073-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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