title: Structure of the ubiquitin-associated domain of p62 (SQSTM1) and implications for mutations that cause Paget's disease of bone.
abstract: The p62 protein (also known as SQSTM1) mediates diverse cellular functions including control of NFkappaB signaling and transcriptional activation. p62 binds non-covalently to ubiquitin and co-localizes with ubiquitylated inclusions in a number of human protein aggregation diseases. Mutations in the gene encoding p62 cause Paget's disease of bone (PDB), a common disorder of the elderly characterized by excessive bone resorption and formation. All of the p62 PDB mutations identified to date cluster within the C-terminal region of the protein, which shows low sequence identity to previously characterized ubiquitin-associated (UBA) domains. We report the first NMR structure of a recombinant polypeptide that contains the C-terminal UBA domain of the human p62 protein (residues 387-436). This sequence, which confers multiubiquitin chain binding, forms a compact three-helix bundle with a structure analogous to the UBA domains of HHR23A but with differences in the loop regions connecting helices that may be involved in binding accessory proteins. We show that the Pro392 --> Leu PDB substitution mutation modifies the structure of the UBA domain by extending the N terminus of helix 1. In contrast to the p62 PDB deletion mutations that remove the UBA domain and ablate multiubiquitin chain binding, the Pro392 --> Leu substitution does not affect interaction of the UBA domain with multiubiquitin chains. Thus, phenotypically identical substitution and deletion mutations do not appear to predispose to PDB through a mechanism dependent on a common loss of ubiquitin chain binding by p62.
authors.affiliation: School of Chemistry, University Park, Nottingham NG7 2RD, United Kingdom.
authors.forename: Barbara
authors.initials: B
authors.lastname: Ciani
authors.forename: Robert
authors.initials: R
authors.lastname: Layfield
authors.forename: James R
authors.initials: JR
authors.lastname: Cavey
authors.forename: Paul W
authors.initials: PW
authors.lastname: Sheppard
authors.forename: Mark S
authors.initials: MS
authors.lastname: Searle
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010001:Osteitis Deformans / Q000235:genetics*; D017433:Protein Structure, Secondary; D011506:Proteins; D000071456:Sequestosome-1 Protein; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D011506:Proteins; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; D025801:Ubiquitin