Dataset Information

Cryo-EM of mammalian PA28??-iCP immunoproteasome reveals a distinct mechanism of proteasome activation by PA28??.

ABSTRACT: The proteasome activator PA28?? affects MHC class I antigen presentation by associating with immunoproteasome core particles (iCPs). However, due to the lack of a mammalian PA28??-iCP structure, how PA28?? regulates proteasome remains elusive. Here we present the complete architectures of the mammalian PA28??-iCP immunoproteasome and free iCP at near atomic-resolution by cryo-EM, and determine the spatial arrangement between PA28?? and iCP through XL-MS. Our structures reveal a slight leaning of PA28?? towards the ?3-?4 side of iCP, disturbing the allosteric network of the gatekeeper ?2/3/4 subunits, resulting in a partial open iCP gate. We find that the binding and activation mechanism of iCP by PA28?? is distinct from those of constitutive CP by the homoheptameric TbPA26 or PfPA28. Our study sheds lights on the mechanism of enzymatic activity stimulation of immunoproteasome and suggests that PA28??-iCP has experienced profound remodeling during evolution to achieve its current level of function in immune response.

SUBMITTER: Chen J

PROVIDER: S-EPMC7854634 | biostudies-literature | 2021 Feb

REPOSITORIES: biostudies-literature

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Cryo-EM of mammalian PA28αβ-iCP immunoproteasome reveals a distinct mechanism of proteasome activation by PA28αβ.

Chen Jinhuan J Wang Yifan Y Xu Cong C Chen Kaijian K Zhao Qiaoyu Q Wang Shutian S Yin Yue Y Peng Chao C Ding Zhanyu Z Cong Yao Y

Nature communications 20210202 1

The proteasome activator PA28αβ affects MHC class I antigen presentation by associating with immunoproteasome core particles (iCPs). However, due to the lack of a mammalian PA28αβ-iCP structure, how PA28αβ regulates proteasome remains elusive. Here we present the complete architectures of the mammalian PA28αβ-iCP immunoproteasome and free iCP at near atomic-resolution by cryo-EM, and determine the spatial arrangement between PA28αβ and iCP through XL-MS. Our structures reveal a slight leaning of ...[more]

PMID: 33531497

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Project description:By monitoring the fragmentation of a GST-BHMT (a protein fusion of glutathionine S-transferase N-terminal to betaine-homocysteine S-methyltransferase) reporter in lysosomes, the GST-BHMT assay has previously been established as an endpoint, cargo-based assay for starvation-induced autophagy that is largely nonselective. Here, we demonstrate that under nutrient-rich conditions, proteasome inhibition by either pharmaceutical or genetic manipulations induces similar autophagy-dependent GST-BHMT processing. However, mechanistically this proteasome inhibition-induced autophagy is different from that induced by starvation as it does not rely on regulation by MTOR (mechanistic target of rapamycin [serine/threonine kinase]) and PRKAA/AMPK (protein kinase, AMP-activated, ? catalytic subunit), the upstream central sensors of cellular nutrition and energy status, but requires the presence of the cargo receptors SQSTM1/p62 (sequestosome 1) and NBR1 (neighbor of BRCA1 gene 1) that are normally involved in the selective autophagy pathway. Further, it depends on ER (endoplasmic reticulum) stress signaling, in particular ERN1/IRE1 (endoplasmic reticulum to nucleus signaling 1) and its main downstream effector MAPK8/JNK1 (mitogen-activated protein kinase 8), but not XBP1 (X-box binding protein 1), by regulating the phosphorylation-dependent disassociation of BCL2 (B-cell CLL/lymphoma 2) from BECN1 (Beclin 1, autophagy related). Moreover, the multimerization domain of GST-BHMT is required for its processing in response to proteasome inhibition, in contrast to its dispensable role in starvation-induced processing. Together, these findings support a model in which under nutrient-rich conditions, proteasome inactivation induces autophagy-dependent processing of the GST-BHMT reporter through a distinct mechanism that bears notable similarity with the yeast Cvt (cytoplasm-to-vacuole targeting) pathway, and suggest the GST-BHMT reporter might be employed as a convenient assay to study selective macroautophagy in mammalian cells.

Dataset Information

Cryo-EM of mammalian PA28??-iCP immunoproteasome reveals a distinct mechanism of proteasome activation by PA28??.

Publications

Cryo-EM of mammalian PA28αβ-iCP immunoproteasome reveals a distinct mechanism of proteasome activation by PA28αβ.

Similar Datasets

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