Structural Analysis of the Bacterial Proteasome Activator Bpa in Complex with the 20S Proteasome

• Published in: Structure (London) 2016-12, Vol.24 (12), p.2138-2151
• Main Authors: Bolten, Marcel, Delley, Cyrille L., Leibundgut, Marc, Boehringer, Daniel, Ban, Nenad, Weber-Ban, Eilika
• Format: Article
• Language: English
• Subjects: bacterial proteasome activator; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Bpa; Cryoelectron Microscopy; degradation; Models, Molecular; Molecular Docking Simulation; Mycobacterium tuberculosis; Mycobacterium tuberculosis - chemistry; Mycobacterium tuberculosis - metabolism; PafE; proteasome; Proteasome Endopeptidase Complex - chemistry; Proteasome Endopeptidase Complex - metabolism; Protein Structure, Secondary
• ISSN: 0969-2126; 1878-4186
• DOI: 10.1016/j.str.2016.10.008

Mycobacterium tuberculosis harbors proteasomes that recruit substrates for degradation through an ubiquitin-like modification pathway. Recently, a non-ATPase activator termed Bpa (bacterial proteasome activator) was shown to support an alternate proteasomal degradation pathway. Here, we present the cryo-electron microscopy (cryo-EM) structure of Bpa in complex with the 20S core particle (CP). For docking into the cryo-EM density, we solved the X-ray structure of Bpa, showing that it forms tight four-helix bundles arranged into a 12-membered ring with a 40 Å wide central pore and the C-terminal helix of each protomer protruding from the ring. The Bpa model was fitted into the cryo-EM map of the Bpa-CP complex, revealing its architecture and striking symmetry mismatch. The Bpa-CP interface was resolved to 3.5 Å, showing the interactions between the C-terminal GQYL motif of Bpa and the proteasome α-rings. This docking mode is related to the one observed for eukaryotic activators with features specific to the bacterial complex. [Display omitted] •Crystal structure of Mycobacterium tuberculosis bacterial proteasome activator Bpa•Stabilization of Bpa-20S complex by way of a genetically encoded crosslinker•Cryo-EM reconstruction reveals architecture of the Bpa-20S complex•High-resolution cryo-EM analysis of the GQYL motif of Bpa and the proteasome Bolten et al. employed a genetically encoded crosslinker to obtain stable complexes of the mycobacterial proteasome and the activator Bpa for cryo-EM reconstruction. The solved crystal structure of Bpa and a high-resolution single-particle cryo-EM reconstruction of the complex elucidates the molecular basis of the interaction mediated by the GQYL motif of Bpa.