The proteasome maturation protein POMP facilitates major steps of 20S proteasome formation at the endoplasmic reticulum

Abstract

The quality control of proteins mediated by the plasticity of the proteasome system is regulated by the timely and flexible formation of this multisubunit proteolytic enzyme complex. Adaptable biogenesis of the 20S proteasome core complex is therefore of vital importance for adjusting to changing proteolytic requirements. However, the molecular mechanism and the cellular sites of mammalian proteasome formation are still unresolved. By using precursor complex-specific antibodies, we now show that the main steps in 20S core complex formation take place at the endoplasmic reticulum (ER). Thereby, the proteasome maturation protein (POMP)-an essential factor of mammalian proteasome biogenesis-interacts with ER membranes, binds to a 1-7 rings, recruits b-subunits stepwise and mediates the association of mammalian precursor complexes with the ER. Thus, POMP facilitates the main steps in 20S core complex formation at the ER to coordinate the assembly process and to provide cells with freshly formed proteasomes at their site of function.

Additive loss-of-function proteasome subunit mutations in CANDLE/PRAAS patients promote type I IFN production

“…Most proteasomal β subunits, except for β3 and β4, are synthesized as proforms that are matured through autocatalytic cleavage during the assembly process, which liberates the active-site threonines (14,15). Most proteasomal β subunits, except for β3 and β4, are synthesized as proforms that are matured through autocatalytic cleavage during the assembly process, which liberates the active-site threonines.…”

“…Equal amounts of TSDGbuffered protein extracts from EBV-B cells, patients' keratinocytes, patients' fibroblasts, siRNA-treated fibroblasts, or transfected HeLa cells were separated on SDS-Laemmli gels (15%) or native PAGE (3%-12%, Invitrogen) and immunoblotted for proteasome subunits as indicated. Primary antibodies were as follows: α6, β1i (LMP2), β5i (LMP7), and POMP are laboratory stocks and were used in former studies (15,16) the manuscript. All authors reviewed and approved the final version of the manuscript.…”

Proteasome assembly from 15S precursors involves major conformational changes and recycling of the Pba1–Pba2 chaperone

“…Contacts to alpha subunits have previously been observed for yeast Ump1 (ref. 34) and its human orthologue 36 . The stretched out conformation of Ump1 and the lack of defined EM density along the projected path fit its description as an intrinsically unstructured protein with little secondary structure elements 37,38 .…”

Targeting the insulin-like growth factor-1 receptor to overcome bortezomib resistance in preclinical models of multiple myeloma

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