Drug target validation of the trypanothione pathway enzymes through metabolic modelling

Authors

  • Viridiana Olin-Sandoval,

    1.  Departamento de Bioquímica, Instituto Nacional de Cardiología Ignacio Chávez, México Distrito Federal, Mexico
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  • Zabdi González-Chávez,

    1.  Departamento de Bioquímica, Instituto Nacional de Cardiología Ignacio Chávez, México Distrito Federal, Mexico
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  • Miriam Berzunza-Cruz,

    1.  Departamento de Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México, México Distrito Federal, Mexico
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  • Ignacio Martínez,

    1.  Departamento de Inmunología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, México Distrito Federal, Mexico
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  • Ricardo Jasso-Chávez,

    1.  Departamento de Bioquímica, Instituto Nacional de Cardiología Ignacio Chávez, México Distrito Federal, Mexico
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  • Ingeborg Becker,

    1.  Departamento de Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México, México Distrito Federal, Mexico
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  • Bertha Espinoza,

    1.  Departamento de Inmunología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, México Distrito Federal, Mexico
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  • Rafael Moreno-Sánchez,

    1.  Departamento de Bioquímica, Instituto Nacional de Cardiología Ignacio Chávez, México Distrito Federal, Mexico
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  • Emma Saavedra

    1.  Departamento de Bioquímica, Instituto Nacional de Cardiología Ignacio Chávez, México Distrito Federal, Mexico
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E. Saavedra, Departamento de Bioquímica, Instituto Nacional de Cardiología Ignacio Chávez, Juan Badiano No. 1 Col. Sección XVI, Tlalpan, México Distrito Federal 14080, Mexico
Fax: + 5255 55730994
Tel: +5255 5573 2911 ext. 1298
E-mail: emma_saavedra2002@yahoo.com

Abstract

A kinetic model of trypanothione [T(SH)2] metabolism in Trypanosoma cruzi was constructed based on enzyme kinetic parameters determined under near-physiological conditions (including glutathione synthetase), and the enzyme activities, metabolite concentrations and fluxes determined in the parasite under control and oxidizing conditions. The pathway structure is characterized by a T(SH)2 synthetic module of low flux and low catalytic capacity, and another more catalytically efficient T(SH)2-dependent antioxidant/regenerating module. The model allowed quantification of the contribution of each enzyme to the control of T(SH)2 synthesis and concentration (flux control and concentration control coefficients, respectively). The main control of flux was exerted by γ-glutamylcysteine synthetase (γECS) and trypanothione synthetase (TryS) (control coefficients of 0.58–0.7 and 0.49–0.58, respectively), followed by spermidine transport (0.24); negligible flux controls by trypantothione reductase (TryR) and the T(SH)2-dependent antioxidant machinery were determined. The concentration of reduced T(SH)2 was controlled by TryR (0.98) and oxidative stress (−0.99); however, γECS and TryS also exerted control on the cellular level of T(SH2) when they were inhibited by more than 70%. The model predicted that in order to diminish the T(SH)2 synthesis flux by 50%, it is necessary to inhibit γECS or TryS by 58 or 63%, respectively, or both by 50%, whereas more than 98% inhibition was required for TryR. Hence, simultaneous and moderate inhibition of γECS and TryS appears to be a promising multi-target therapeutic strategy. In contrast, use of highly potent and specific inhibitors for TryR and the antioxidant machinery is necessary to affect the antioxidant capabilities of the parasites.

Database 
The glutathione synthetase gene sequences from the Ninoa and Queretaro strains have been submitted to the GenBank database under accession numbers HQ398240 and HQ398239, respectively

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