Crystal structure of the catalytic domain of the Bacillus cereus SleB protein, important in cortex peptidoglycan degradation during spore germination.
The SleB protein is one of two redundant cortex-lytic enzymes (CLEs) that initiate the degradation of cortex peptidoglycan (PG), a process essential for germination of spores of Bacillus species, including Bacillus anthracis. SleB has been characterized as a soluble lytic transglycosylase that specifically recognizes spore cortex PG and catalyzes the cleavage of glycosidic bonds between N-acetylmuramic acid (NAM) and N-acetylglucosamine residues with concomitant formation of a 1,6-anhydro bond in the NAM residue. We found that like the full-length Bacillus cereus SleB, the catalytic C-terminal domain (SleB(C)) exhibited high degradative activity on cortex PG in vitro, although SleB's N-terminal domain, thought to bind PG, was inactive. The 1.85-Å crystal structure of SleB(C) reveals an ellipsoid molecule with two distinct domains dominated by either α helices or β strands. The overall fold of SleB closely resembles that of the catalytic domain of the family 1 lytic transglycosylases but with a completely different topological arrangement. Structural analysis shows that an invariant Glu157 of SleB is in a position equivalent to that of the catalytic glutamate in other lytic transglycosylases. Indeed, SleB bearing a Glu157-to-Gln mutation lost its cortex degradative activity completely. In addition, the other redundant CLE (called CwlJ) in Bacillus species likely has a three-dimensional structure similar to that of SleB, including the invariant putative catalytic Glu residue. SleB and CwlJ may offer novel targets for the development of anti-spore agents.
Department of Molecular, Microbial and Structural Biology University of Connecticut Health Center, Farmington, Connecticut, USA.
Yunfeng
Y
Li
Kai
K
Jin
Barbara
B
Setlow
Peter
P
Setlow
Bing
B
Hao
D000117:Acetylglucosamine / Q000737:chemistry; D000581:Amidohydrolases / Q000737:chemistry* / Q000235:genetics; D001409:Bacillus cereus / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006867:Hydrolases / Q000235:genetics; D009112:Muramic Acids / Q000737:chemistry; D010457:Peptidoglycan / Q000378:metabolism*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013171:Spores, Bacterial / Q000201:enzymology* / Q000378:metabolism
D001426:Bacterial Proteins; D009112:Muramic Acids; D010457:Peptidoglycan; C101656:SleB protein, Bacillus; C031651:N-acetylmuramic acid; C433796:CwlJ protein, Bacillus subtilis; D006867:Hydrolases; D000581:Amidohydrolases; D000117:Acetylglucosamine