Phospho-ubiquitin

Molecular indicators reshaping diagnostics in mitochondrial and neurodegenerative diseases.

Phospho-ubiquitin: A Biomarker for Mitochondrial Dysfunction

Phosphoubiquitin (pUb), a phosphorylated form of ubiquitin, has emerged as a potential biomarker for mitochondrial dysfunction and related neurodegenerative diseases. This post-translational modification is primarily generated by the kinase PINK1 (PTEN-induced kinase 1) in response to mitochondrial damage. Upon mitochondrial stress, PINK1 accumulates on the outer mitochondrial membrane and phosphorylates ubiquitin at serine 65, facilitating the recruitment and activation of the E3 ligase Parkin, which triggers mitophagy—the selective clearance of damaged mitochondria.

A Window Into Mitophagy

Elevated levels of phosphoubiquitin have been observed in cells and tissues undergoing active mitophagy, making it a valuable readout for mitochondrial quality control. Its accumulation is particularly relevant in Parkinson’s disease and related disorders, where mutations in PINK1 or Parkin impair mitophagy. Thus, phosphoubiquitin serves not only as a mechanistic indicator of mitochondrial stress response but also as a promising biomarker for diagnosing and monitoring the progression or therapeutic response in mitochondrial and neurodegenerative diseases.

Mitochondrial Ubiquitome: Precision Profiling

Ubiquitination of outer-mitochondrial membrane (OMM) proteins of mitochondria is a hallmark feature of mitophagy. Primarily driven by the PINK1/Parkin E3 ligase activation feedback loop, damaged mitochondria become a hot spot of ubiquitination. Ubiquitination of TOM20, VDACs, MFN1, MFN2, CISD1 and MIRO1 among others have been reported. Progenra has developed a highly sensitive ELISA-based assay to detect ubiquitination of multiple OMM proteins after mitochondrial damage. We have leveraged this assay to characterize our mitophagy enhancer molecules.

Figure 5. PINK1 activation on damaged mitochondria stimulates the recruitment and activation of Parkin E3 ligase which results in robust ubiquitination of multiple OMM proteins. Progenra has developed highly sensitive ELISA assays to detect OMM protein ubiquitination.