Tissue Transglutaminase 2 Catalyzed Cross-Links Between Lysine and Glutamine in α-Synuclein Induced Neurodegenerative Diseases

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2022-12-03

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Abstract

A common hallmark associated in neurodegenerative diseases (ND) are the appearance of abnormal proteins, such as mutations, misfolding, cross-linking, and amino acid extensions generated by nucleotide repeats. Parkinson’s disease (PD), the 14th-leading cause of death in the United States and the second most common neurodegenerative disorder after Alzheimer’s disease (AD). PD is characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) associated with the accumulation of α-synuclein. α-synuclein is a 140 amino acid aggregate-prone protein that contributes to the development of PD, dementia, and other ND, referred to as synucleinopathies. This protein is the major constituent of Lewy bodies (LB) and LB neurites, which are pathological protein aggregates that accumulate in the nerve cells of patients with PD, PD dementia (PDD), and LB dementia (LBD) and increase throughout the nervous system during the progression of the disease. Tissue transglutaminase (TG2), a calcium-dependent enzyme that catalyzes the formation of isopeptide bonds of numerous substrates and implicated in the involvement of ND. I demonstrated TG2 was a key driver in the formation of toxic α-synuclein multimers by cross-linking specific glutamine residues into covalent, protease-resistant epsilon-gamma glutamyl lysine isopeptide bonds. Here, I employed a cost-efficient and innovative technology system that screened specific peptides at the molecular level, elucidated the amine acceptor involved in the post-translational modification (PTM) in α-synuclein aggregates by investigating the enzyme-substrate relationship catalyzed by TG2. A novel in vitro microfluidic peptide-microarray biochip (PepArray™) technology platform was used to analyze 3968 immobilized peptides for identification of specific modified glutamine residues when reacted with TG2, where substrates were available in a controlled enzymatic reaction chamber. Proteomics-based mass spectrometer Orbitrap mass analyzer coupled with an IonTrap analyzer were used to identify specific modified glutamine residues which showed cross-links of Q24 at K6, and highly reactive Q62 at K96. Identification of these disease state substrates supply an intervention into managing cluster growth and better understand the pathogenic properties of α-synucleins which influence in the progression of ND. These proteomic technologies can provide significant insights into substrate specificity and their functions through in vitro technology.

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Keywords

Α-synuclein, Neurodegenerative diseases, Parkinson's disease, TG2, Cross-link, Mass spectrometry, Micro peparray

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