title: Crystal structure of Bacillus anthracis transpeptidase enzyme CapD.
abstract: 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.
authors.affiliation: Biosciences Division, Midwest Center for Structural Genomics and Structural Biology Center, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Ruiying
authors.initials: R
authors.lastname: Wu
authors.forename: Stefan
authors.initials: S
authors.lastname: Richter
authors.forename: Rong-guang
authors.initials: RG
authors.lastname: Zhang
authors.forename: Valerie J
authors.initials: VJ
authors.lastname: Anderson
authors.forename: Dominique
authors.initials: D
authors.lastname: Missiakas
authors.forename: Andrzej
authors.initials: A
authors.lastname: Joachimiak
mesh_terms: 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
chemical_list: D001426:Bacterial Proteins; D004151:Dipeptides; D005723:gamma-Glutamyltransferase