Proteins and lipids of glycosomal membranes from Leishmania tarentolae and Trypanosoma brucei

Claudia Colasante,Aloysius G M Tielens,Theresa Manful,Christine Clayton,Thomas Ruppert,Jaap J Van Hellemond,Frank Voncken

doi:10.12688/f1000research.2-27.v1

Abstract

In kinetoplastid protists, several metabolic pathways, including glycolysis and purine salvage, are located in glycosomes, which are microbodies that are evolutionarily related to peroxisomes. With the exception of some potential transporters for fatty acids, and one member of the mitochondrial carrier protein family, proteins that transport metabolites across the glycosomal membrane have yet to be identified. We show here that the phosphatidylcholine species composition of Trypanosoma brucei glycosomal membranes resembles that of other cellular membranes, which means that glycosomal membranes are expected to be impermeable to small hydrophilic molecules unless transport is facilitated by specialized membrane proteins. Further, we identified 464 proteins in a glycosomal membrane preparation from Leishmania tarentolae. The proteins included approximately 40 glycosomal matrix proteins, and homologues of peroxisomal membrane proteins - PEX11, GIM5A and GIM5B; PXMP4, PEX2 and PEX16 - as well as the transporters GAT1 and GAT3. There were 27 other proteins that could not be unambiguously assigned to other compartments, and that had predicted trans-membrane domains. However, no clear candidates for transport of the major substrates and intermediates of energy metabolism were found. We suggest that, instead, these metabolites are transported via pores formed by the known glycosomal membrane proteins.

Highlights

In kinetoplastid protists, several metabolic pathways, including glycolysis, purine salvage and ether lipid biosynthesis, are located in a microbody, the glycosome[1,2], which is evolutionarily related to peroxisomes
The total amount of membrane protein obtained from 3 × 1010 T. brucei was so low that we doubted that any lower-abundance proteins would be detected by mass spectrometry
We decided to isolate glycosomes from the related kinetoplastid L. tarentolae to increase the sensitivity for the detection of even low-abundant glycosomal membrane proteins

Summary

Introduction

Several metabolic pathways, including glycolysis, purine salvage and ether lipid biosynthesis, are located in a microbody, the glycosome[1,2], which is evolutionarily related to peroxisomes. Specific transporters would be required if the membrane were impermeable to molecules of the size of glycolytic intermediates, such as glucose, phosphate, malate, pyruvate, phosphoenolpyruvate and various triosephosphates. In 1987, the first protein profile of glycosomal membranes from Trypanosoma brucei was published[6]. It revealed two abundant proteins of 24 and 26 kDa, which were later shown to be trypanosome homologues of the peroxisome biogenesis protein PEX117–9. Subsequent studies, including two of the glycosomal proteome[1,10], revealed several more trypanosome PEX proteins that are predicted to be membrane-bound, such as PEX211,12, PEX1013, PEX1213, PEX1314 and PEX1415. MCP6 is found preferentially in the glycosomal membranes of bloodstreamform trypanosomes, whereas in procyclic forms, it is predominantly targeted to the mitochondria[17]

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Conclusion