Structures of the Trypanosome Cell

 

 

 

 

A kinetoplast inside a mitochondria. (UCLA)

Acidocalcisomes contain dense, dark material. (KBD)

 

 

A transferrin receptor "hiding" between surface glycoproteins (Borst and Fairlamb, 1998).

The kinetoplast and flagellae divide first. (UCLA)

 

 

 

 

 

Why are studies of the trypanosome cell so important? Not only will a better understanding of trypanosome cell biology help us find new ways to combat trypanosomiasis, it also has the potential to give us new insights into eukaryotic cell biology in general. This is because trypanosomes are brimming with unusual and fascinating organelles and other structural components. They are also now relatively easy to culture and study.

Here are just a few interesting aspects of trypanosome cell research:

  • The KINETOPLAST was the first discovered example of DNA in the cytoplasm (rev. Vickerman and Coombs, 1999). It is a mass of circular DNA inside the trypanosome’s mitochondrion, and it is attached to the basal bodies of the flagellum. It undergoes repression and activation so that the trypanosome can switch its pattern of respiration to match its host’s energy source. Division of the kinetoplast is a reliable marker of a certain point in the cell cycle, making it important in cell cycle studies (Ploubidou et al., 1999).
  • The ACIDOCALCISOME is an organelle first described in trypanosomes (Docampo et al., 1995). It is similar to volutin granules present in some other microorganisms. Its contents are very acidic and include a high density of calcium and magnesium, and its membrane contains many ion exchangers, including a novel category of Ca2+ pump. It is thought that the acidocalcisome functions in calcium storage and regulation, and the huge internal concentration of polyphosphates suggests an additional role in energy storage (Docampo and Moreno, 2001).

  • The GLYCOSOME is an organelle similar to the peroxisome, except that it houses much of glycolysis, purine salvage, and ether-lipid biosynthesis. To learn more about the role of the glycosome in trypanosome respiration, click here.

  • The trypanosome CYTOSKELETON is heavily microtubule-based, and contains many interesting structures. For a summary of cytoskeleton structures and recent findings, click here.
  • The trypanosome plasma membrane is covered with hundreds of important RECEPTORS, which are hidden from the immune system beneath the antigenic coat or inside the flagellar pocket invaginations. These receptors are involved in the uptake of all the necessary host resources, from glucose to purines to iron. Because many of these receptors are very different from those found in mammals, they may make excellent drug targets in the near future (reviewed in Borst, 1998).
  • The CELL CYCLE of trypanosomes may have novel checkpoints unlike those of other eukaryotes, recent evidence suggests. Mitosis failures always lead to cytokinesis failures in most organisms, but a trypanosome cell in which mitosis has been disrupted can still undergo cytokinesis- the mitosis checkpoint seems to be missing! There details are still very unclear, but some scientists hypothesize that one of the checkpoints may be regulated by division of the kinetoplast (Ploubidou et al. 1999).

Unique organelles, unusual receptors, and novel cell cycle checkpoints- these are only a few examples of what sets trypanosomes apart from the rest of us. The information we gain from these structures and others in the next few years could give us new treatment avenues, direct us to similar structures in other microorganisms, and give us information about how and when our own cell structures evolved. Please refer to our links and list of references to begin accessing the enormous wealth of information on this topic.

Works Cited

Borst, P. and A.H. Fairlamb. 1998. Surface receptors and transporters of Trypanosoma brucei. Annu. Rev. Microbiol. 52: 745-78.

Docampo, R., D.A. Scott, A.E. Vercesi, and S.N.J. Moreno. 1995. Intracellular Ca2+ storage in acidocalcisomes of Trypanosoma cruzi. Biochem J. 310: 1005-12.

Docampo, R., and S.N.J. Moreno. 2001. The acidocalcisome. Mol. Biochem. Parasitol. 33:151-159.

Ploubidou, A., D.R. Robinson, R.C. Docherty, E.O. Ogbadoyi, and K. Gull. 1999. Evidence for novel cell cycle checkpoints in trypanosomes: kinetoplast segregation and cytokinesis in the absence of mitosis. J. Cell Sci.112: 4641-4650.

Vickerman, K. and G.H. Coombs. 1999. Protozoan paradigms for cell biology. J. Cell Sci. 112: 2797-2798.

Revised 24 April 2003. Send corrections or comments to enderli@earlham.edu