Structure of the Bacillus anthracis Sortase A Enzyme Bound to Its Sorting Signal

• Published in: The Journal of biological chemistry 2015-10, Vol.290 (42), p.25461-25474
• Main Authors: Chan, Albert H., Yi, Sung Wook, Terwilliger, Austen L., Maresso, Anthony W., Jung, Michael E., Clubb, Robert T.
• Format: Article
• Language: English
• Subjects: Bacillus anthracis; enzyme mechanism; enzyme regulation; enzyme substrate complex; nuclear magnetic resonance (NMR); protein dynamic; protein structure; sortase A; SrtA; transpeptidase
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M115.670984

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 (BaSrtA) enzyme. Previously, we discovered that the class A BaSrtA 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 BaSrtA 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. Background: The Bacillus anthracis sortase A (BaSrtA) enzyme attaches virulence factors to the cell surface. Results: The structure of BaSrtA bound to a substrate analog reveals key amino acids involved in substrate recognition and catalysis. Conclusion:BaSrtA modulates substrate access using a unique N-terminal appendage. Significance: This research could facilitate the design of new anti-infective agents that work by disrupting surface protein display.