Mercaptopyruvate sulfurtransferase and cysteine biosynthetic pathways in Leishmania

Williams, Roderick Adeyinka Malcolm (2003) Mercaptopyruvate sulfurtransferase and cysteine biosynthetic pathways in Leishmania. PhD thesis, University of Glasgow.

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Abstract

Coping with oxidative stress is vital for survival of the intracellular parasite Leishmania, but the complex biochemical mechanisms involved are not fully understood. This study focused on enzymes of cysteine metabolism in Leishmania and the parts they play. Mercaptopyruvate sulfurtransferase (EC 2.8.1.2) of Leishmania major and L. mexicana and serine acetyltransferase (EC 2.1.3.30), cysteine synthase (EC 4.2.99.8) and cystathionine b-synthase (EC 4.2.1.22) of Leishmania major have been cloned, expressed as active enzymes in Escherichia coli, and characterised. The leishmanial mercaptopyruvate sulfurtransferase is structurally peculiar in possessing a C-terminal domain of some 70 amino acids. Homologous genes of T. cruzi and T. brucei encode enzymes with a similar C-terminal domain, which suggests that the feature, not known in any other sulfurtranferase, is a characteristic of trypanosomatid parasites. Short truncations of the C-terminal domain resulted in misfolded, inactive proteins, demonstrating that the domain plays some key role in facilitating correct folding of the enzymes. The recombinant sulfurtransferase exhibit high activity towards 3-mercaptopyruvate and catalyse the transfer of sulfane to cyanide to form thiocyanate and sulfide. The sulfide can react with O-acetyl serine to yield cysteine through the action of cysteine synthase. They also use thiosulfate as a substrate and mercaptoethanol, glutathione, cysteine or reduced thioredoxin as the accepting nucleophile, the latter being oxidised. Mercaptopyruvate sulfurtransferase and cysteine synthase are expressed in all life cycle stages of Leishmania and the expression levels are increased under hypo-sulfur stress. The expression level of mercaptopyruvate sulfurtransferase is also increased under oxidative stress whereas overexpression of serine acetyltransferase, cysteine synthase and cystathionine beta-synthase in Leishmania promastigotes produced cell lines resistant to the oxidants hydrogen peroxide (0.5 mM), tert-butyl hydroperoxide (10 mM) and cumene hydroperoxide (10 mM).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QR Microbiology > QR180 Immunology
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Infection Immunity and Inflammation
Funder's Name: UNSPECIFIED
Supervisor's Name: Coombs, G.H. and Mottram, J.C.
Date of Award: 2003
Depositing User: Mrs Marie Cairney
Unique ID: glathesis:2003-8317
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 21 Jul 2017 16:14
Last Modified: 21 Jul 2017 16:14
URI: http://theses.gla.ac.uk/id/eprint/8317

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