Cloning, heterologous expression, and characterization of three aquaglyceroporins from Trypanosoma brucei.
Trypanosoma brucei, causative for African sleeping sickness, relies exclusively on glycolysis for ATP production. Under anaerobic conditions, glucose is converted to equimolar amounts of glycerol and pyruvate, which are both secreted from the parasite. As we have shown previously, glycerol transport in T. brucei occurs via specific membrane proteins (Wille, U., Schade, B., and Duszenko, M. (1998) Eur. J. Biochem. 256, 245-250). Here, we describe cloning and biochemical characterization of the three trypanosomal aquaglyceroporins (AQP; TbAQP1-3), which show a 40-45% identity to mammalian AQP3 and -9. AQPs belong to the major intrinsic protein family and represent channels for small non-ionic molecules. Both TbAQP1 and TbAQP3 contain two highly conserved NPA motifs within the pore-forming region, whereas TbAQP2 contains NSA and NPS motifs instead, which are only occasionally found in AQPs. For functional characterization, all three proteins were heterologously expressed in yeast and Xenopus oocytes. In the yeast fps1Delta mutant, TbAQPs suppressed hypoosmosensitivity and rendered cells to a hyper-osmosensitive phenotype, as expected for unregulated glycerol channels. Under iso- and hyperosmotic conditions, these cells constitutively released glycerol, consistent with a glycerol efflux function of TbAQP proteins. TbAQP expression in Xenopus oocytes increased permeability for water, glycerol and, interestingly, dihydroxyacetone. Except for urea, TbAQPs were virtually impermeable for other polyols; only TbAQP3 transported erythritol and ribitol. Thus, TbAQPs represent mainly water/glycerol/dihydroxyacetone channels involved in osmoregulation and glycerol metabolism in T. brucei. This function and especially the so far not investigated transport of dihydroxyacetone may be pivotal for the survival of the parasite survival under non-aerobic or osmotic stress conditions.
Biochemical Institute, Department of Pharmaceutical Biochemistry, and Institute of Physiology, University of Tübingen, 72076 Tübingen Germany.
Nestor L
NL
Uzcategui
Alexander
A
Szallies
Slavica
S
Pavlovic-Djuranovic
Monica
M
Palmada
Katherine
K
Figarella
Christoph
C
Boehmer
Florian
F
Lang
Eric
E
Beitz
Michael
M
Duszenko
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D051398:Aquaporin 1; D051399:Aquaporin 2; D051400:Aquaporin 3; D020346:Aquaporins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D015152:Blotting, Northern; D003001:Cloning, Molecular; D004098:Dihydroxyacetone / Q000737:chemistry; D005822:Genetic Vectors; D005990:Glycerol / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D009995:Osmosis; D010641:Phenotype; D010802:Phylogeny; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D013997:Time Factors; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000378:metabolism*; D014867:Water / Q000737:chemistry; D014981:Xenopus; D014982:Xenopus laevis
C109669:AQP9 protein, human; D051399:Aquaporin 2; D020346:Aquaporins; D014867:Water; D051398:Aquaporin 1; D051400:Aquaporin 3; D004098:Dihydroxyacetone; D005990:Glycerol