Dissecting beta-ring assembly pathway of the mammalian 20S proteasome |
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Authors: | Hirano Yuko Kaneko Takeumi Okamoto Kenta Bai Minghui Yashiroda Hideki Furuyama Kaori Kato Koichi Tanaka Keiji Murata Shigeo |
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Affiliation: | Laboratory of Frontier Science, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan. |
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Abstract: | The 20S proteasome is the catalytic core of the 26S proteasome. It comprises four stacked rings of seven subunits each, alpha(1-7)beta(1-7)beta(1-7)alpha(1-7). Recent studies indicated that proteasome-specific chaperones and beta-subunit appendages assist in the formation of alpha-rings and dimerization of half-proteasomes, but the process involved in the assembly of beta-rings is poorly understood. Here, we clarify the mechanism of beta-ring formation on alpha-rings by characterizing assembly intermediates accumulated in cells depleted of each beta-subunit. Starting from beta2, incorporation of beta-subunits occurs in an orderly manner dependent on the propeptides of beta2 and beta5, and the C-terminal tail of beta2. Unexpectedly, hUmp1, a chaperone functioning at the final assembly step, is incorporated as early as beta2 and is required for the structural integrity of early assembly intermediates. We propose a model in which beta-ring formation is assisted by both intramolecular and extrinsic chaperones, whose roles are partially different between yeast and mammals. |
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Keywords: | assembly chaperone propeptide proteasome ubiquitin |
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