NMR structure of the ubiquitin associated (UBA) domain of p62 (SQSTM1) in complex with ubiquitin. RDC refined
[SQSTM_HUMAN] Defects in SQSTM1 are a cause of Paget disease of bone (PDB) [MIM:602080]. PDB is a metabolic bone disease affecting the axial skeleton and characterized by focal areas of increased and disorganized bone turn-over due to activated osteoclasts. Manifestations of the disease include bone pain, deformity, pathological fractures, deafness, neurological complications and increased risk of osteosarcoma. PDB is a chronic disease affecting 2 to 3% of the population above the age of 40 years.        Note=In a cell model for Huntington disease (HD), appears to form a shell surrounding aggregates of mutant HTT that may protect cells from apoptosis, possibly by recruiting autophagosomal components to the polyubiquitinylated protein aggregates.
[SQSTM_HUMAN] Required both for the formation and autophagic degradation of polyubiquitin-containing bodies, called ALIS (aggresome-like induced structures). Links ALIS to the autophagic machinery via direct interaction with MAP1 LC3 family members. May regulate the activation of NFKB1 by TNF-alpha, nerve growth factor (NGF) and interleukin-1. May play a role in titin/TTN downstream signaling in muscle cells. May regulate signaling cascades through ubiquitination. Adapter that mediates the interaction between TRAF6 and CYLD (By similarity). May be involved in cell differentiation, apoptosis, immune response and regulation of K(+) channels.          
Publication Abstract from PubMed
The p62 protein functions as a scaffold in signaling pathways that lead to activation of NF-kappaB and is an important regulator of osteoclastogenesis. Mutations affecting the receptor activator of NF-kappaB signaling axis can result in human skeletal disorders, including those identified in the C-terminal ubiquitin-associated (UBA) domain of p62 in patients with Paget disease of bone. These observations suggest that the disease may involve a common mechanism related to alterations in the ubiquitin-binding properties of p62. The structural basis for ubiquitin recognition by the UBA domain of p62 has been investigated using NMR and reveals a novel binding mechanism involving a slow exchange structural reorganization of the UBA domain to a "bound" non-canonical UBA conformation that is not significantly populated in the absence of ubiquitin. The repacking of the three-helix bundle generates a binding surface localized around the conserved Xaa-Gly-Phe-Xaa loop that appears to optimize both hydrophobic and electrostatic surface complementarity with ubiquitin. NMR titration analysis shows that the p62-UBA binds to Lys 48-linked di-ubiquitin with approximately 4-fold lower affinity than to mono-ubiquitin, suggesting preferential binding of the p62-UBA to single ubiquitin units, consistent with the apparent in vivo preference of the p62 protein for Lys 63-linked polyubiquitin chains (which adopt a more open and extended structure). The conformational switch observed on binding may represent a novel mechanism that underlies specificity in regulating signalinduced protein recognition events.
Ubiquitin recognition by the ubiquitin-associated domain of p62 involves a novel conformational switch.,Long J, Gallagher TR, Cavey JR, Sheppard PW, Ralston SH, Layfield R, Searle MS J Biol Chem. 2008 Feb 29;283(9):5427-40. Epub 2007 Dec 14. PMID:18083707
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.