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1.
PLoS One ; 5(8): e12282, 2010 Aug 19.
Artículo en Inglés | MEDLINE | ID: mdl-20808867

RESUMEN

Myosins are a multimember family of motor proteins with diverse functions in eukaryotic cells. African trypanosomes possess only two candidate myosins and thus represent a useful system for functional analysis of these motors. One of these candidates is an unusual class I myosin (TbMyo1) that is expressed at similar levels but organized differently during the life cycle of Trypanosoma brucei. This myosin localizes to the polarized endocytic pathway in bloodstream forms of the parasite. This organization is actin dependent. Knock down of TbMyo1 results in a significant reduction in endocytic activity, a cessation in cell division and eventually cell death. A striking morphological feature in these cells is an enlargement of the flagellar pocket, which is consistent with an imbalance in traffic to and from the surface. In contrast TbMyo1 is distributed throughout procyclic forms of the tsetse vector and a loss of approximately 90% of the protein has no obvious effects on growth or morphology. These results reveal a life cycle stage specific requirement for this myosin in essential endocytic traffic and represent the first description of the involvement of a motor protein in vesicle traffic in these parasites.


Asunto(s)
Miosina Tipo I/metabolismo , Vesículas Transportadoras/metabolismo , Trypanosoma brucei brucei/citología , Trypanosoma brucei brucei/enzimología , Secuencia de Aminoácidos , Animales , Regulación de la Expresión Génica , Datos de Secuencia Molecular , Miosina Tipo I/sangre , Miosina Tipo I/química , Miosina Tipo I/genética , Estructura Terciaria de Proteína , Transporte de Proteínas , Ratas , Trypanosoma brucei brucei/metabolismo
2.
FEBS J ; 276(23): 7187-99, 2009 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-19895576

RESUMEN

African trypanosomes possess high levels of alanine aminotransferase (EC 2.6.1.2), although the function of their activity remains enigmatic, especially in slender bloodstream forms where the metabolism of ketoacids does not occur. Therefore, the gene for alanine aminotransferase enzyme in Trypanosoma brucei (TbAAT) was characterized and its function assessed using a combination of RNA interference and gene knockout approaches. Surprisingly, as much as 95% or more of the activity appears to be unnecessary for growth of either bloodstream or procyclic forms respiring on glucose. A combination of RNA interference and NMR spectroscopy revealed an important role for the activity in procyclic forms respiring on proline. Under these conditions, the major end product of proline metabolism is alanine, and a reduction in TbAAT activity led to a proportionate decrease in the amount of alanine excreted along with an increase in the doubling time of the cells. These results provide evidence of a role for alanine aminotransferase in the metabolism of proline in African trypanosomes by linking glutamate produced by the initial oxidative steps of the pathway with pyruvate produced by the final oxidative step of the pathway. This step appears to be essential when proline is the primary carbon source, which is likely to be the physiological situation in the tsetse fly vector.


Asunto(s)
Alanina Transaminasa/metabolismo , Prolina/metabolismo , Proteínas Protozoarias/metabolismo , Trypanosoma brucei brucei/enzimología , Alanina Transaminasa/genética , Animales , Secuencia de Bases , Células Cultivadas , Cinética , Datos de Secuencia Molecular , Resonancia Magnética Nuclear Biomolecular , Proteínas Protozoarias/genética , Interferencia de ARN , Trypanosoma brucei brucei/metabolismo
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