Trypanosoma brucei: characterisation of a life cycle stage-specific G-protein.
G-proteins have important and diverse roles in cellular signaling in higher eukaryotes but as yet little is known about the involvement of these GTP-binding proteins in protozoan parasites. Bacterial toxin-catalysed ADP-ribosylation, routinely used in the characterisation of G-proteins in higher eukaryotes, was used to determine whether functional G-protein homologues could be detected in Trypanosoma brucei. A 43-kDa polypeptide that was ADP-ribosylated in the presence of pertussis toxin was identified in membrane fractions. This polypeptide was also recognised by an antibody generated against a peptide sequence representing a mammalian GO alpha G-protein subunit. GTP and GTP gamma S (a nonhydrolysable analogue of GTP) abolished the ADP-ribosylation reaction, indicating that the 43-kDa polypeptide also binds GTP. Furthermore, this T. brucei G-protein is present in bloodstream but not procyclic life cycle stages. Using an in situ GTP binding assay, a further group of small-molecular-size GTP-binding proteins which are present in both bloodstream and procyclic stages have been identified. This demonstration of G-proteins in T. brucei suggests possible intracellular mechanisms that may be involved in the transduction of host or other parasite signals.
Coulter
L J
LJ
Wellcome Unit of Molecular Parasitology, Anderson College, Glasgow University, United Kingdom.
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D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D015153:Blotting, Western; D002772:Cholera Toxin / Q000494:pharmacology; D003429:Cross Reactions; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D019204:GTP-Binding Proteins / Q000032:analysis* / Q000276:immunology / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D007106:Immune Sera / Q000276:immunology; D008163:Luminescent Measurements; D009243:NAD / Q000378:metabolism; D037342:Pertussis Toxin; D015800:Protozoan Proteins / Q000032:analysis* / Q000276:immunology / Q000378:metabolism; D013045:Species Specificity; D014346:Trypanosoma brucei brucei / Q000737:chemistry* / Q000187:drug effects / Q000254:growth & development; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007106:Immune Sera; D015800:Protozoan Proteins; D010566:Virulence Factors, Bordetella; D009243:NAD; D000246:Adenosine Diphosphate Ribose; D006160:Guanosine Triphosphate; D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins