Identification and Characterization of Abnormal Succinylation in Mitochondrial DNA Depletion Syndrome Caused by Defective SUCLA2

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Title: Identification and Characterization of Abnormal Succinylation in Mitochondrial DNA Depletion Syndrome Caused by Defective SUCLA2
Author: Pällijeff, Pieti
Other contributor: Helsingin yliopisto, Lääketieteellinen tiedekunta
University of Helsinki, Faculty of Medicine
Helsingfors universitet, Medicinska fakulteten
Publisher: Helsingin yliopisto
Date: 2021
Language: eng
Thesis level: master's thesis
Degree program: Translationaalisen lääketieteen maisteriohjelma (Translational Medicine)
Master's Programme in Translational Medicine
Magisterprogrammet i translationell medicin
Specialisation: Cross-disciplinary translational medicine
Cross-disciplinary translational medicine
Cross-disciplinary translational medicine
Abstract: Recently, several novel post-translational modifications (PTMs) have been identified as important regulators in biology. Succinylation, the reversible addition of a succinyl group from a free succinyl-CoA into a protein lysine, is one such novel PTM. The last decade of research has unveiled succinylation as a powerful regulator of metabolism, prevalent in every organism it has been studied in and with functional effects on target proteins in several key metabolic pathways. A major contribution of this thesis is to catalogue the recent advances in succinylation research into the most comprehensive literary review currently available on succinylation. While the biological role of this PTM is being established, the relevance of succinylation in human disease has remained unclear. Meanwhile, mitochondrial DNA depletion syndrome caused by defective SUCLA2 (SUCLA2 disease) is a progressive hereditary mitochondrial disease with no available treatment. SUCLA2 disease is caused by defective mutations in the ß-subunit SUCLA2 of the TCA cycle enzyme succinyl-CoA synthetase. While the characteristic manifestations, including impairment of respiratory complexes, and the etiological mutations in this disease are well established, the pathogenic model for SUCLA2 disease has remained incomplete. As succinyl-CoA synthetase shares a substrate, succinyl-CoA, with succinylation, this thesis set out to probe SUCLA2 mutants for a potential succinylation phenotype. An extensive hypersuccinylation phenotype was characterized in fibroblasts and tissue samples from SUCLA2 mutant patients by immunochemical methods. The hypersuccinylation target identities in SUCLA2 mutants were revealed with proteomics by mass-spectrometry. Hypersuccinylation in SUCLA2 mutants was shown to be enriched in proteins participating in mitochondrial energy metabolism, including respiratory complex proteins. In addition, several novel metabolic phenotypes were characterized in SUCLA2 mutants with metabolomics by mass-spectrometry, most prominently a significant depletion of aspartate metabolism. While identification of extensive hypersuccinylation in SUCLA2 mutants establishes a novel concept of succinylation relevance in human metabolic disease, the prospect of altered regulation of the respiratory complexes due to hypersuccinylation lays the foundation for a novel pathogenic model for SUCLA2 disease. Meanwhile, the observed novel metabolic phenotypes significantly contribute to the current understanding on SUCLA2 mutant metabolism and inspire a hypothetical model on how the defective succinyl-CoA synthetase could be circumvented in the TCA cycle of SUCLA2 mutants.
Subject: Succinylation
post-translational modification
succinyl-CoA synthetase
mitochondrial disease
mitochondrial DNA depletion syndrome
metabolic regulation
TCA cycle
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