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

July 28, 2017

Title

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

Author

Marcel Bolten, Cyrille L. Delley, Marc Leibundgut, Daniel Boehringer, Nenad Ban, Eilika Weber-Ban

Year

2016

Journal

Structure

Abstract

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.

Instrument

J-715

Keywords

Circular dichroism, Secondary structure, Biochemistry