4ADY:
reference: The Structure of the 26S Proteasome Subunit Rpn2 Reveals Its PC Repeat Domain as a Closed Toroid of Two Concentric alpha-Helical Rings., He J, Kulkarni K, da Fonseca PC, Krutauz D, Glickman MH, Barford D, Morris EP, Structure. 2012 Mar 7;20(3):513-21. PMID: 22405010

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