title: Structural and Functional Characterization of an Ancient Bacterial Transglutaminase Sheds Light on the Minimal Requirements for Protein Cross-Linking.
abstract: Transglutaminases are best known for their ability to catalyze protein cross-linking reactions that impart chemical and physical resilience to cellular structures. Here, we report the crystal structure and characterization of Tgl, a transglutaminase from the bacterium Bacillus subtilis. Tgl is produced during sporulation and cross-links the surface of the highly resilient spore. Tgl-like proteins are found only in spore-forming bacteria of the Bacillus and Clostridia classes, indicating an ancient origin. Tgl is a single-domain protein, produced in active form, and the smallest transglutaminase characterized to date. We show that Tgl is structurally similar to bacterial cell wall endopeptidases and has an NlpC/P60 catalytic core, thought to represent the ancestral unit of the cysteine protease fold. We show that Tgl functions through a unique partially redundant catalytic dyad formed by Cys116 and Glu187 or Glu115. Strikingly, the catalytic Cys is insulated within a hydrophobic tunnel that traverses the molecule from side to side. The lack of similarity of Tgl to other transglutaminases together with its small size suggests that an NlpC/P60 catalytic core and insulation of the active site during catalysis may be essential requirements for protein cross-linking.
authors: Catarina G
authors: CG
authors: Fernandes
authors: Diana
authors: D
authors: Plácido
authors: Diana
authors: D
authors: Lousa
authors: José A
authors: JA
authors: Brito
authors: Anabela
authors: A
authors: Isidro
authors: Cláudio M
authors: CM
authors: Soares
authors: Biotechnology Branch, Centers for Disease Control and Prevention , Atlanta, Georgia 30333, United States.
authors: Jan
authors: J
authors: Pohl
authors: Maria A
authors: MA
authors: Carrondo
authors: Margarida
authors: M
authors: Archer
authors: Adriano O
authors: AO
authors: Henriques
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D020134:Catalytic Domain; D003432:Cross-Linking Reagents / Q000737:chemistry; D018360:Crystallography, X-Ray; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D017354:Point Mutation; D011487:Protein Conformation; D017510:Protein Folding; D011503:Transglutaminases / Q000737:chemistry* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D003432:Cross-Linking Reagents; D011503:Transglutaminases