The Evolutionary History of MAPL (Mitochondria-Associated Protein Ligase) and Other Eukaryotic BAM/GIDE Domain Proteins

Exploring the Role of Ubiquitin-Proteasome System in the Pathogenesis of Parkinson's Disease

Parkinson's disease (PD) is a prevalent neurodegenerative disorder among the elderly population. The pathogenesis of PD encompasses genetic alterations, environmental factors, and age-related neurodegenerative processes. Numerous studies have demonstrated that aberrant functioning of the ubiquitin-proteasome system (UPS) plays a crucial role in the initiation and progression of PD. Notably, E3 ubiquitin ligases serve as pivotal components determining substrate specificity within UPS and are intimately associated with the regulation of various proteins implicated in PD pathology. This review comprehensively summarizes the mechanisms by which E3 ubiquitin ligases and deubiquitinating enzymes modulate PD-associated proteins and signaling pathways, while exploring the intricate relationship between UPS dysfunctions and PD etiology. Furthermore, this article discusses recent research advancements regarding inhibitors targeting PD-related E3 ubiquitin ligases.

Mul1 restrains Parkin-mediated mitophagy in mature neurons by maintaining ER-mitochondrial contacts

Chronic mitochondrial stress associates with major neurodegenerative diseases. Recovering stressed mitochondria constitutes a critical step of mitochondrial quality control and thus energy maintenance in early stages of neurodegeneration. Here, we reveal Mul1-Mfn2 pathway that maintains neuronal mitochondrial integrity under stress conditions. Mul1 deficiency increases Mfn2 activity that triggers the first phasic mitochondrial hyperfusion and also acts as an ER-Mito tethering antagonist. Reduced ER-Mito coupling leads to increased cytoplasmic Ca²⁺ load that activates calcineurin and induces the second phasic Drp1-dependent mitochondrial fragmentation and mitophagy. Overexpressing Mfn2, but not Mfn1, mimics Mul1-deficient phenotypes, while expressing PTPIP51, an ER-Mito anchoring protein, suppresses Parkin-mediated mitophagy. Thus, by regulating mitochondrial morphology and ER-Mito contacts, Mul1-Mfn2 pathway plays an early checkpoint role in maintaining mitochondrial integrity. Our study provides new mechanistic insights into neuronal mitochondrial maintenance under stress conditions, which is relevant to several major neurodegenerative diseases associated with mitochondrial dysfunction and altered ER-Mito interplay.

Little is known about the pathways that maintain mitochondrial structure and function under neuronal stress conditions. Here, authors demonstrate that the Mul1-Mfn2 pathway plays a checkpoint role in maintaining mitochondrial integrity and energy maintenance by ensuring ER-mitochondrial tethering and preventing mitophagy.

Mitochondrial E3 ubiquitin ligase 1: A key enzyme in regulation of mitochondrial dynamics and functions

Mitochondrial E3 ubiquitin ligase 1 (Mul1) is a multifunctional mitochondrial membrane protein with its RING domain exposed to the cytoplasm. On the one hand, Mul1 functions as a ubiquitin-ligase to ubiquitinate a bunch of signal molecules, such as mitofusin2 (Mfn2), Akt, p53 and ULK1, through its RING finger domain, leading to proteins degradation. On the other hand, Mul1 acts as a small ubiquitin-like modifiers (SUMO) E3 ligase to sumoylate certain proteins, such as dynamin-related protein 1 (Drp1), enhancing protein stabilization. Through the dual functions of ubiquitination and SUMOylation, Mul1 involves in regulation of many physiological and pathological processes, such as mitochondrial dynamics, cell growth, apoptosis and mitophagy. In addition, Mul1 can also directly activate or interact with some proteins, such as NF-κB and JNK, to take part in the regulation of cellular apoptosis. This review summarizes recent progress in relevant studies on the physiological and pathological functions of Mul1 and pays special attention to its role in regulation of mitochondrial dynamics.