OPTN, TBK1 bind ubiquitinated MOM proteins

Damaged mitochondria are flagged by ubiquitin (Ub) chains that are conjugated to proteins at the mitochondrial outer membrane (MOM). This process is regulated by the PINK1-mediated phosphorylation of Parkin (PRKN), an E3 ubiquitin protein ligase that, when activated, ubiquitinates a broad range of MOM proteins (Gladkova C et al., 2018; Sauve V et al., 2022). The conjugated Ub chains are recognized by cargo receptors such as sequestosome 1 (p62 or SQSTM1), nuclear dot protein 52 (NDP52) and optineurin (OPTN, also called FIP2 and NRP), which tether damaged mitochondria to components of the autophagy machinery promoting selective autophagy of mitochondria (mitophagy) (Onishi M et al., 2021; Goodall EA et al., 2022; Adriaenssens E et al., 2022). <p>OPTN is an Ub-binding adaptor protein, which is recruited to damaged mitochondria in a PINK1:PRKN-dependent manner (Wong YC & Holzbaur EL 2014; Heo JM et al., 2015; Lazarou M et al., 2015; reviewed in Qiu Y et al., 2022). Structural and biochemical studies demonstrate that OPTN binds polyUb chains via its C-terminal Ub binding domain (UBD) with a preference for M1- and K63-linked polyUb chains (Gleason CE et al., 2011; Nakazawa S et al., 2016; Li F et al., 2018). A surface plasmon resonance (SPR) and ITC binding assays show that OPTN and M1-linked polyUb form a complex with an equilibrium dissociation constant (Kd) value in the micromolar range (Nakazawa S et al., 2016; Li F et al., 2018). <p>OPTN interacts with TANK-binding kinase 1 (TBK1) (Morton S et al., 2008; Mankouri J et al., 2010; Gleason CE et al., 2011; Heo JM et al., 2015; Li F et al., 2016; Yamano K et al., 2024). Specifically, the N-terminal coiled coil domain of OPTN interacts with the C-terminal domain of TBK1 in human embryonic kidney 293T (HEK293T) cells (Morton S et al., 2008; Meena NP et al., 2016; Li F et al., 2016) with the micromolar affinity (Li F et al., 2016). Both constitutive (Mankouri J et al., 2010; Gleason CE et al., 2011; Richter B et al., 2016) and stimuli-induced (Pourcelot M et al., 2016; Meena NP et al., 2016) interactions between OPTN and TBK1 are observed in mouse and human cells. TBK1 has been shown to phosphorylate OPTN at S177, S473 or S513 enhancing the polyUb-binding function of OPTN (Richter B et al., 2016; Li F et al., 2018). TBK1-mediated phosphorylation of OPTN at S473 has been shown to broaden the binding specificity of OPTN to other polyUb chains including K48-linked (Li F et al., 2018). OPTN and TBK1 function in selective autophagy are critical for maintaining cellular homeostasis, and dysregulation of OPTN:TBK1-mediated autophagy has been implicated in disease pathogenesis (Wong YC & Holzbaur EL 2014; Harding O et al., 2021). <p>Interactions between OPTN and other proteins such as autophagy-related protein 9A (ATG9A) (Yamano K et al., 2020), myosin VI (MYO6), microtubule-associated proteins 1A/1B light chain 3B (MAP1LC3B or LC3) are implicated in autophagy. <p>This Reactome event shows association between TBK1, OPTN, and polyUb moieties of MOM proteins.<br>

受损的线粒体通过泛素（Ub）链进行标记，这些链与线粒体外膜（MOM）上的蛋白质结合。此过程受PINK1介导的Parkin（PRKN）磷酸化调控，Parkin是一种E3泛素蛋白连接酶，在激活状态下，对广泛的MOM蛋白进行泛素化（Gladkova C 等人，2018；Sauve V 等人，2022）。结合的Ub链被如密封素1（p62或SQSTM1）、核点蛋白52（NDP52）和光神经素（OPTN，亦称FIP2和NRP）等载体受体识别，这些受体将受损的线粒体锚定到自噬机器的组成部分，从而促进线粒体的选择性自噬（mitophagy）（Onishi M 等人，2021；Goodall EA 等人，2022；Adriaenssens E 等人，2022）。<p>OPTN是一种泛素结合适配蛋白，以PINK1:PRKN依赖的方式招募到受损的线粒体上（Wong YC & Holzbaur EL 2014；Heo JM 等人，2015；Lazarou M 等人，2015；Qiu Y 等人，2022综述）。结构和生化研究表明，OPTN通过其C端泛素结合结构域（UBD）与多Ub链结合，对M1-和K63连接的多Ub链具有偏好性（Gleason CE 等人，2011；Nakazawa S 等人，2016；Li F 等人，2018）。表面等离子体共振（SPR）和ITC结合实验表明，OPTN与M1连接的多Ub形成了一个平衡解离常数（Kd）值在微摩尔范围内的复合物（Nakazawa S 等人，2016；Li F 等人，2018）。<p>OPTN与TANK结合激酶1（TBK1）（Morton S 等人，2008；Mankouri J 等人，2010；Gleason CE 等人，2011；Heo JM 等人，2015；Li F 等人，2016；Yamano K 等人，2024）相互作用。具体而言，OPTN的N端螺旋卷曲结构域与HEK293T细胞（Morton S 等人，2008；Meena NP 等人，2016；Li F 等人，2016）中的TBK1的C端结构域相互作用，具有微摩尔的亲和力（Li F 等人，2016）。在鼠和人的细胞中观察到OPTN与TBK1之间的构成性（Mankouri J 等人，2010；Gleason CE 等人，2011；Richter B 等人，2016）和刺激诱导性（Pourcelot M 等人，2016；Meena NP 等人，2016）相互作用。TBK1已被证明在S177、S473或S513处磷酸化OPTN，增强OPTN的多Ub结合功能（Richter B 等人，2016；Li F 等人，2018）。TBK1在S473处介导的OPTN磷酸化已被证明可以扩展OPTN对其他多Ub链（包括K48连接的）的结合特异性（Li F 等人，2018）。OPTN和TBK1在选择性自噬中的作用对于维持细胞稳态至关重要，OPTN:TBK1介导的自噬失调已被认为是疾病发病机制的原因（Wong YC & Holzbaur EL 2014；Harding O 等人，2021）。<p>OPTN与其他蛋白质如自噬相关蛋白9A（ATG9A）（Yamano K 等人，2020）、肌球蛋白VI（MYO6）、微管相关蛋白1A/1B轻链3B（MAP1LC3B或LC3）之间的相互作用与自噬有关。<p>此Reactome事件显示了TBK1、OPTN和MOM蛋白的多Ub片段之间的关联。