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Study of the substrate specificity of the LACTB tumour suppressor enzyme
Baudyšová, Alžběta ; Kečkéšová, Zuzana (advisor) ; Janečková, Lucie (referee)
Serine beta-lactamase-like protein (LACTB) is a tumour suppressor that modulates mitochondrial lipid metabolism and induces differentiation of breast cancer cells. This is achieved by the LACTB-dependent downregulation of phosphatidylserine- decarboxylase (PISD) which subsequently leads to decreases in the amounts of phosphatidylethanolamines and lysophosphatidylethanolamines in mitochondrial membranes. However, PISD was shown to not be a direct substrate of the LACTB enzyme what leaves the identity of the LACTB substrate an open question. To fill this important gap in the mechanism of the LACTB tumour suppressive pathway, this diploma thesis was focused on finding a physiological substrate of LACTB via Proteomic Identification of protease Cleavage Sites (PICS) assay. For this purpose, the other sub-aims of this project were to isolate recombinant wild-type LACTB and its catalytic mutant, to reveal ideal in vitro conditions for LACTB activity and to find out the requirements needed for LACTB multimerization. My results show that in vitro activity of LACTB is increased in the presence of higher pH and calcium ions. I also show that higher LACTB multimeric forms are bound together via disulfide bonds as they disintegrate after treatment with dithiothreitol. Furthermore, and most importantly, I show...
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Molecular requirements of LACTB-induced tumor suppression
Jakoubě, Pavel ; Kečkéšová, Zuzana (advisor) ; Rohlenová, Kateřina (referee)
LACTB is a recently discovered mitochondrial tumour suppressor protein operating in many different types of tissues. Its mechanism-of-action seems to be context dependent as it has been shown to suppress carcinogenesis through the induction of cell cycle arrest, apoptosis, differentiation and suppression of EMT. These processes can be further dependent on alterations of lipid metabolism and interactions with additional tumour suppressors and signalling pathways. LACTB is derived from bacterial penicillin binding proteins, is localized to the mitochondrial intermembrane space and possesses enzymatic activity. It was shown to form filaments, which consist of two intertwined antiparallel chains, suggesting its role in the organisation of mitochondrial intermembrane space. In the first aim of my thesis, I wanted to examine in more detail the molecular requirement for LACTB's filament formation with the specific focus on the role of disulphide bonds in this process. In the second aim of my thesis, I intended to uncover the binding partners of LACTB, which might have a role in the filament formation. Realizing both aims will uncover important requirements for the proper folding and biological activity of LACTB. Key words: LACTB, tumour suppressor, cancer, structure, disulphide bonds, protein interactions
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Study of the substrate specificity of the LACTB tumour suppressor enzyme
Baudyšová, Alžběta ; Kečkéšová, Zuzana (advisor) ; Janečková, Lucie (referee)
Serine beta-lactamase-like protein (LACTB) is a tumour suppressor that modulates mitochondrial lipid metabolism and induces differentiation of breast cancer cells. This is achieved by the LACTB-dependent downregulation of phosphatidylserine- decarboxylase (PISD) which subsequently leads to decreases in the amounts of phosphatidylethanolamines and lysophosphatidylethanolamines in mitochondrial membranes. However, PISD was shown to not be a direct substrate of the LACTB enzyme what leaves the identity of the LACTB substrate an open question. To fill this important gap in the mechanism of the LACTB tumour suppressive pathway, this diploma thesis was focused on finding a physiological substrate of LACTB via Proteomic Identification of protease Cleavage Sites (PICS) assay. For this purpose, the other sub-aims of this project were to isolate recombinant wild-type LACTB and its catalytic mutant, to reveal ideal in vitro conditions for LACTB activity and to find out the requirements needed for LACTB multimerization. My results show that in vitro activity of LACTB is increased in the presence of higher pH and calcium ions. I also show that higher LACTB multimeric forms are bound together via disulfide bonds as they disintegrate after treatment with dithiothreitol. Furthermore, and most importantly, I show...
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Mitochondrial beta-lactamase and its role in humans
Baudyšová, Alžběta ; Šácha, Pavel (advisor) ; Pecina, Petr (referee)
Cancer is one of the most frequent causes of death. Fortunately, human body has a number of various mechanisms that protect cells from tumorigenic transformation. One of those mechanisms are tumor suppressor genes. The latest described tumor suppressor gene encodes LACTB protein. LACTB is the mammalian homolog of bacterial beta-lactamases and penicillin binding proteins (PBPs). PBPs are involved in construction of bacterial cell walls (specifically in the synthesis of peptidoglycan) and they could be inhibited by penicillin antibiotics. Beta-lactamases are able to break the beta-lactam ring of penicillin and provide resistance to the antibiotics. The main topic of this work will be the LACTB protein. LACTB is localizated in the intermembrane space of mammalian mitochondria. Here it forms filaments whose physiological function still remains unknown. LACTB, apart from its connection with cancer, was also associated with obesity and penicillin allergy. Main focus of this work will be to gather all known information about the LACTB protein and put them into a wider context.
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