Specificity in protein-ligand recognition: characterisation of a novel conformational switch in the p62 UBA domain interaction with ubiquitin

多功能p62蛋白（也称为SQSTM1）调节多种细胞过程，包括与骨细胞（破骨细胞）和神经元功能相关的体内相互作用伙伴。影响p62的突变是导致佩吉特骨病（PDB）的常见原因，然而，这种骨骼疾病的确切发病机制尚不清楚。泛素相关（UBA）结构域在许多蛋白质中被鉴定为泛素结合基序；p62中的PDB突变主要发生在其c端UBA结构域，这意味着这些病理性突变可能损害p62蛋白与已经标记有泛素的破骨细胞蛋白靶点的相互作用。最近，在PDB患者中发现了p62序列其他部分的突变，这些突变仍然导致泛素结合功能的丧失或损害。在对p62的UBA结构域及其与泛素和多泛素链相互作用的结构研究中，我们最近证明了结合泛素后UBA的一种新的结构重组，这似乎为泛素结合的特定调节提供了一种独特的机制，考虑到p62参与多种信号复合物。这种结合机制表明，UBA结构域的PDB突变可以通过影响这种构象平衡的直接和间接机制影响泛素结合特异性。我们计划研究更大的p62蛋白片段相互作用的分子起源，而不仅仅是UBA结构域，并以PDB突变为有价值的工具，研究泛素识别的潜在生理基础。

The multi-functional p62 protein (also known as SQSTM1) regulates a diverse range of cellular processes involving in vivo interaction partners relevant to bone cell (osteoclast) and neuronal function. Mutations affecting p62 are a common cause of Paget's disease of bone (PDB), however, the precise disease mechanism in this skeletal disorder is unclear. Ubiquitin-associated (UBA) domains have been identified in many proteins as ubiquitin (Ub)-binding motifs; PDB mutations in p62 occur principally within its C-terminal UBA domain, with the implication that these pathological mutations may compromise interactions of the p62 protein with osteoclast protein targets already tagged with ubiquitin. More recently, mutations in other parts of the p62 sequence have been identified in PDB patients which still result in loss or impairment of ubiquitin-binding function. In structural studies of the UBA domain of p62 and its interaction with ubiquitin and poly-ubiquitin chains, we have recently demonstrated a novel structural re-organisation of the UBA upon binding ubiquitin that appears to provide an unique mechanism for specific regulation of ubiquitin-binding, given the participation of p62 in multiple signalling complexes. This binding mechanism suggests that PDB mutations in the UBA domain could affect ubiquitin binding specificity through both direct and indirect mechanisms that affect this conformational equilibrium. We plan to investigate the molecular origins of the interaction of much larger fragments of the p62 protein than simply the UBA domain, and investigate the underlying physiological basis for ubiquitin recognition with PDB mutations as valuable tools.