The capsule and S-layer: two independent and yet compatible macromolecular structures in Bacillus anthracis.
Bacillus anthracis, the etiological agent of anthrax, is a gram-positive spore-forming bacterium. Fully virulent bacilli are toxinogenic and capsulated. Two abundant surface proteins, including the major antigen, are components of the B. anthracis surface layer (S-layer). The B. anthracis paracrystalline S-layer has previously only been found in noncapsulated vegetative cells. Here we report that the S-layer proteins are also synthesized under conditions where the poly-gamma-D-glutamic acid capsule is present. Structural and immunological analyses show that the capsule is exterior to and completely covers the S-layer proteins. Nevertheless, analysis of single and double S-layer protein mutants shows that the presence of these proteins is not required for normal capsulation of the bacilli. Similarly, the S-layer proteins assemble as a two-dimensional crystal, even in the presence of the capsule. Thus, both structures are compatible, and yet neither is required for the correct formation of the other.
Mesnage
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S
Toxines et Pathogénie Bactériennes (CNRS URA 1858), Institut Pasteur, Paris, France.
Tosi-Couture
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E
Gounon
P
P
Mock
M
M
Fouet
A
A
D000818:Animals; D000907:Antibodies, Bacterial; D000918:Antibody Specificity; D000942:Antigens, Bacterial / Q000032:analysis; D001408:Bacillus anthracis / Q000166:cytology* / Q000276:immunology / Q000648:ultrastructure; D016667:Bacterial Capsules / Q000032:analysis* / Q000648:ultrastructure; D001426:Bacterial Proteins / Q000032:analysis* / Q000096:biosynthesis / Q000235:genetics; D017353:Gene Deletion; D005798:Genes, Bacterial / Q000235:genetics; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D011099:Polyglutamic Acid / Q000096:biosynthesis
D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; C055764:S-layer proteins; D011099:Polyglutamic Acid