Structural investigation of Mycobacterial protein complexes involved in the stationary phase stress response

Abstract

Large protein complexes play key roles in mediating biological processes in the cell. Little structural information is known on the protein complex mediators governing persistence in the host for Mycobacterium tuberculosis (Mtb). We applied the ‘shotgun EM’ method for the structural characterisation of protein complexes produced after exposure to stationary phase stress for the model Mycobacterium, M smegmatis (Msm). We identified glutamine synthetase I, essential for Mtb virulence, in addition to bacterioferritin, critical for Mtb iron regulation, and encapsulin, which produces a cage-like structure to enclose target proteins. Further investigation found that encapsulin carries dye-decolourising peroxidase (DyP), a potent protein antioxidant, as the primary cargo during stationary phase stress. Our ‘proof-of-concept’ application of this method offers insight into identifying potential key-mediators in Mtb persistence.