Crystal structure of Bacillus anthracis transpeptidase enzyme CapD.
Bacillus anthracis elaborates a poly-gamma-d-glutamic acid capsule that protects bacilli from phagocytic killing during infection. The enzyme CapD generates amide bonds with peptidoglycan cross-bridges to anchor capsular material within the cell wall envelope of B. anthracis. The capsular biosynthetic pathway is essential for virulence during anthrax infections and can be targeted for anti-infective inhibition with small molecules. Here, we present the crystal structures of the gamma-glutamyltranspeptidase CapD with and without alpha-l-Glu-l-Glu dipeptide, a non-hydrolyzable analog of poly-gamma-d-glutamic acid, in the active site. Purified CapD displays transpeptidation activity in vitro, and its structure reveals an active site broadly accessible for poly-gamma-glutamate binding and processing. Using structural and biochemical information, we derive a mechanistic model for CapD catalysis whereby Pro(427), Gly(428), and Gly(429) activate the catalytic residue of the enzyme, Thr(352), and stabilize an oxyanion hole via main chain amide hydrogen bonds.
Wu
Ruiying
R
Biosciences Division, Midwest Center for Structural Genomics and Structural Biology Center, Argonne National Laboratory, Argonne, Illinois 60439, USA.
Richter
Stefan
S
Zhang
Rong-guang
RG
Anderson
Valerie J
VJ
Missiakas
Dominique
D
Joachimiak
Andrzej
A
D001408:Bacillus anthracis / Q000201:enzymology*; D016667:Bacterial Capsules / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004151:Dipeptides / Q000737:chemistry* / Q000378:metabolism; D008956:Models, Chemical; D008958:Models, Molecular; D020836:Protein Structure, Quaternary / Q000502:physiology; D005723:gamma-Glutamyltransferase / Q000737:chemistry* / Q000378:metabolism
D001426:Bacterial Proteins; D004151:Dipeptides; D005723:gamma-Glutamyltransferase