Structure of the Bacillus anthracis Sortase A Enzyme Bound to Its Sorting Signal: A FLEXIBLE AMINO-TERMINAL APPENDAGE MODULATES SUBSTRATE ACCESS.
The endospore forming bacterium Bacillus anthracis causes lethal anthrax disease in humans and animals. The ability of this pathogen to replicate within macrophages is dependent upon the display of bacterial surface proteins attached to the cell wall by the B. anthracis Sortase A ((Ba)SrtA) enzyme. Previously, we discovered that the class A (Ba)SrtA sortase contains a unique N-terminal appendage that wraps around the body of the protein to contact the active site of the enzyme. To gain insight into its function, we determined the NMR structure of (Ba)SrtA bound to a LPXTG sorting signal analog. The structure, combined with dynamics, kinetics, and whole cell protein display data suggest that the N terminus modulates substrate access to the enzyme. We propose that it may increase the efficiency of protein display by reducing the unproductive hydrolytic cleavage of enzyme-protein covalent intermediates that form during the cell wall anchoring reaction. Notably, a key active site loop (β7/β8 loop) undergoes a disordered to ordered transition upon binding the sorting signal, potentially facilitating recognition of lipid II.
From the Department of Chemistry and Biochemistry, UCLA-DOE Institute of Genomics and Proteomics, and the Molecular Biology Institute, University of California, Los Angeles, California 90095 and.
Albert H
AH
Chan
From the Department of Chemistry and Biochemistry.
Sung Wook
SW
Yi
the Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030.
Austen L
AL
Terwilliger
the Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas 77030.
Anthony W
AW
Maresso
From the Department of Chemistry and Biochemistry.
Michael E
ME
Jung
From the Department of Chemistry and Biochemistry, UCLA-DOE Institute of Genomics and Proteomics, and the Molecular Biology Institute, University of California, Los Angeles, California 90095 and rclubb@mbi.ucla.edu.
Robert T
RT
Clubb
D019881:Aminoacyltransferases / Q000737:chemistry* / Q000378:metabolism; D001408:Bacillus anthracis / Q000201:enzymology* / Q000472:pathogenicity; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D021382:Protein Sorting Signals; D013379:Substrate Specificity
D001426:Bacterial Proteins; D021382:Protein Sorting Signals; D019881:Aminoacyltransferases; C120542:sortase A; D003546:Cysteine Endopeptidases
Bacillus anthracis; SrtA; enzyme mechanism; enzyme regulation; enzyme substrate complex; nuclear magnetic resonance (NMR); protein dynamic; protein structure; sortase A; transpeptidase