title: Bacterial proteasome activator bpa (rv3780) is a novel ring-shaped interactor of the mycobacterial proteasome.
abstract: The occurrence of the proteasome in bacteria is limited to the phylum of actinobacteria, where it is maintained in parallel to the usual bacterial compartmentalizing proteases. The role it plays in these organisms is still not fully understood, but in the human pathogen Mycobacterium tuberculosis (Mtb) the proteasome supports persistence in the host. In complex with the ring-shaped ATPase Mpa (called ARC in other actinobacteria), the proteasome can degrade proteins that have been post-translationally modified with the prokaryotic ubiquitin-like protein Pup. Unlike for the eukaryotic proteasome core particle, no other bacterial proteasome interactors have been identified to date. Here we describe and characterize a novel bacterial proteasome activator of Mycobacterium tuberculosis we termed Bpa (Rv3780), using a combination of biochemical and biophysical methods. Bpa features a canonical C-terminal proteasome interaction motif referred to as the HbYX motif, and its orthologs are only found in those actinobacteria encoding the proteasomal subunits. Bpa can inhibit degradation of Pup-tagged substrates in vitro by competing with Mpa for association with the proteasome. Using negative-stain electron microscopy, we show that Bpa forms a ring-shaped homooligomer that can bind coaxially to the face of the proteasome cylinder. Interestingly, Bpa can stimulate the proteasomal degradation of the model substrate β-casein, which suggests it could play a role in the removal of non-native or damaged proteins.
authors.affiliation: ETH Zurich, Institute for Molecular Biology & Biophysics, Zurich, Switzerland.
authors.forename: Cyrille L
authors.initials: CL
authors.lastname: Delley
authors.affiliation: ETH Zurich, Institute for Molecular Biology & Biophysics, Zurich, Switzerland.
authors.forename: Juerg
authors.initials: J
authors.lastname: Laederach
authors.affiliation: ETH Zurich, Institute for Molecular Biology & Biophysics, Zurich, Switzerland.
authors.forename: Michal
authors.initials: M
authors.lastname: Ziemski
authors.affiliation: ETH Zurich, Institute for Molecular Biology & Biophysics, Zurich, Switzerland.
authors.forename: Marcel
authors.initials: M
authors.lastname: Bolten
authors.affiliation: ETH Zurich, Institute for Molecular Biology & Biophysics, Zurich, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Boehringer
authors.affiliation: ETH Zurich, Institute for Molecular Biology & Biophysics, Zurich, Switzerland.
authors.forename: Eilika
authors.initials: E
authors.lastname: Weber-Ban
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D017124:Conserved Sequence; D004789:Enzyme Activation; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000201:enzymology*; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry*; D054730:Protein Interaction Domains and Motifs
chemical_list: D001426:Bacterial Proteins; D046988:Proteasome Endopeptidase Complex