ISSN:
1365-2958
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
,
Medicine
Notes:
Electron microscopy of isolated cell walls of the ancient bacterium Thermus thermophilus revealed that most of the peptidoglycan (PG) surface, apart from the septal region, was shielded against specific αPG antibodies. On the other hand, an antiserum raised against S-layer-attached cell wall fragments (αSAC) bound to most of the surface except for the septal regions. Treatments with α-amylase and pronase E made the entire cell wall surface uniformly accessible to αPG and severely decreased the binding of αSAC. We concluded that a layer of strongly bound secondary cell wall polymers (SCWPs) covers most of the cell wall surface in this ancient bacterium. A preliminary analysis revealed that such SCWPs constitute 14% of the cell wall and are essentially composed of sugars. Enzyme treatments of the cell walls revealed that SCWP was required in vitro for the binding of the S-layer protein through the S-layer homology (SLH) motif. The csaB gene was necessary for the attachment of the S-layer–outer membrane (OM) complex to the cell wall in growing cells of T. thermophilus. In vitro experiments confirmed that cell walls from a csaB mutant bound to the S-layer with a much lower affinity (∼1/10) than that of the wild type. CsaB was found to be required for pyruvylation of components of the SCWP and for immunodetection with α-SAC antiserum. Therefore, the S-layer–OM complex of T. thermophilus binds to the cell wall through the SLH motif of the S-layer protein via a strong interaction with a highly immunogenic pyruvylated component of the SCWP. Immuno-cross-reactive compounds were detected with αSAC on cell walls of other Thermus spp. and in the phylogenetically related microorganism Deinococcus radiodurans. These results imply that the interaction between the SLH motif and pyruvylated components of the cell wall arose early during bacterial evolution as an ancestral mechanism for anchoring proteins and outer membranes to the cell walls of primitive bacteria.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-2958.2004.04011.x
