Investigating post-translational modifications of mitochondrial proteins

: mitochondrial fission factor (MFF) and PTEN-induced kinase 1 (PINK1)

Abstract

Proteins can undergo a variety of reversible and irreversible modifications following translation, collectively referred to as post-translational modifications (PTMs). These modifications provide cells an extra layer of regulating many characteristics of proteins, such as their subcellular localization and function. The cross-regulation and co-regulation of PTMs adds to the complexity of this process. Some common PTMs explored in this thesis include phosphorylation, SUMOylation, and ubiquitination of the mitochondrial proteins, mitochondrial fission factor (MFF) and PTEN-induced kinase 1 (PINK1).

The work presented in the first part of this thesis explores the interplay between phosphorylation, SUMOylation, and ubiquitination of the outer mitochondrial membrane protein, MFF. I briefly examine the potential role of one sentrin-specific protease, SENP6, in editing poly-SUMO chains on MFF. I also identify MARCH5 as a putative ubiquitin E3 ligase for MFF. Additionally, I show that ubiquitinated MFF is a substrate for PINK1-mediated phosphorylation, potentially in a SUMO-dependent manner.

PTEN-induced kinase 1 (PINK1) is a mitochondrial kinase that plays a pivotal role in the clearance of damaged mitochondria. The majority of this thesis explores the SUMOylation of PINK1, namely with first identifying PINK1 as a novel SUMO2/3 substrate. PINK1 is likely SUMOylated by the E3 ligase, mitochondrial anchored protein ligase (MAPL), in a lysine-independent manner. I briefly explore the functional role of PINK1 SUMOylation, with preliminary data suggesting that the role of MAPL in regulating basal mitophagy requires PINK1, and this process occurs possibly via PINK1 SUMOylation. Ultimately, this suggests that PINK1 SUMOylation potentially plays a protective role in regulating PINK1-dependent mitophagy. Insights into the exact mechanism and function of PINK1 SUMOylation could be used to modulate this process for future therapeutic applications.

Date of Award	4 Feb 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jeremy M Henley (Supervisor)