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bioRxiv · 10.1101/105866

Structure of a AAA+ unfoldase in the process of unfolding substrate

Ripstein, Z. A.·Huang, R.·Augustyniak, R.·Kay, L. E.·Rubinstein, J. L.
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Abstract

AAA+ unfoldases are thought to unfold substrate through the central pore of their hexameric structures, but how this process occurs is not known. VAT, the Thermoplasma acidophilum homologue of eukaryotic CDC48/p97, works in conjunction with the proteasome to degrade misfolded or damaged proteins. We show that in the presence of ATP, VAT with its regulatory N-terminal domains removed unfolds other VAT complexes as substrate. We captured images of this transient process by electron cryomicroscopy (cryo-EM) to reveal the structure of the substrate-bound intermediate. Substrate binding breaks the six-fold symmetry of the complex, allowing five of the six VAT subunits to constrict into a tight helix that grips an ~80 [A] stretch of unfolded protein. The structure suggests a processive hand-over-hand unfolding mechanism, where each VAT subunit releases the substrate in turn before re-engaging further along the target protein, thereby unfolding it.

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Ripstein, Z. A., Huang, R., Augustyniak, R., Kay, L. E., Rubinstein, J. L.. 2017-02-03. Structure of a AAA+ unfoldase in the process of unfolding substrate. https://doi.org/10.1101/105866

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