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bioRxiv · 10.1101/2024.11.04.621988

Structure of Blm10:13S proteasome intermediate reveals parallel assembly pathways for the proteasome core particle

Kaur, M.·Chen, X.·Lee, S. Y.·Weaver, T. M.·Freudenthal, B. D.·Walters, K.·Roelofs, J.
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Abstract

Proteasomes are formed by chaperone-assisted assembly of core particles (CPs) and regulatory particles (RPs). The CP chaperone dimer Pba1/Pba2 binds early to proteasome subunits, and is thought to be replaced by Blm10 to form Blm10:CP, which promotes ATP-independent degradation of disordered proteins. Here, we present evidence of distinct parallel assembly pathways for CP by solving five cryo-EM structures including a Blm10:13S pre-assembly intermediate. Our data conflict with the current model of Blm10 and Pba1/Pba2 sequential activity in a single assembly pathway, as we find their CP binding is mutually exclusive and both are present on early and late assembly intermediates. CP affinity for Pba1/Pba2 is reduced during maturation, promoting Pba1/Pba2 release. We find Blm10 undergoes no such affinity switch, suggesting this pathway predominantly yields mature Blm10-bound CP. Altogether, our findings conflict with the current paradigm of sequential CP binding to instead indicate parallel assembly pathways by Pba1/Pba2 and Blm10.

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Kaur, M., Chen, X., Lee, S. Y., Weaver, T. M., Freudenthal, B. D., Walters, K., Roelofs, J.. 2024-11-05. Structure of Blm10:13S proteasome intermediate reveals parallel assembly pathways for the proteasome core particle. https://doi.org/10.1101/2024.11.04.621988

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