Protein turnover and differentiation in Leishmania

Abstract

Leishmania occurs in several developmental forms and thus undergoes complex cell differentiation events during its life-cycle. Those are required to allow the parasite to adapt to the different environmental conditions. The sequencing of the genome of L. major has facilitated the identification of the parasite's vast arsenal of proteolytic enzymes, a few of which have already been carefully studied and found to be important for the development and virulence of the parasite. This review focuses on these peptidases and their role in the cellular differentiation of Leishmania through their key involvement in a variety of degradative pathways in the lysosomal and autophagy networks.

Fig. 1

Changes in cell shape during the Leishmania life-cycle. (a) Scanning electron microscope images of the main Leishmania major life-cycle stages, the procyclic and metacyclic promastigotes were grown in culture, the amastigote was isolated from an infected macrophage isolated from a mouse. (b) Schematic representation of the main intracellular organelles from Leishmania promastigote (left) or amastigote (right) forms. The flagellar pocket marks the anterior end of the cell.

Fig. 2

Clans and families of Leishmania major peptidases. Nomenclature is based on the MEROPS database (http://merops.sanger.ac.uk/). Numbers in brackets represents the estimated number of peptidases in each Family, taken from Ivens et al. (2005) and the MEROPS database (release 7.7, January 2007).

Fig. 3

Labelling of the lysosomal compartment of Leishmania major using a GFP-fused syntaxin. GFP-LmjF19.0120 (green) was observed in a live procyclic promastigote (a, top), metacyclic promastigote (a, bottom) and amastigote within a mouse macrophage (b). Nuclear (n) and mitochondrial (kinetoplast, k) DNA were stained with DAPI (blue). The cells were visualised by differential interference contrast (DIC) and enlarged images are displayed on the right. Scale bar is 10 μm.

Fig. 4

The distribution of GFP-ATG8 expressed in live Leishmania during its life-cycle. Examples of GFP-ATG8-labelled autophagosomes are indicated with arrows. GFP-ATG8 has a cytosolic distribution in replicating procyclic promastigotes, but some relocates to autophagosomes during metacyclogenesis or under starvation conditions. GFP-ATG8 is located in the MVT-lysosome in metacyclic promastigotes as the autophagosomes fuse with lysosomes to form autolysosomes. During differentiation from a metacyclic promastigote to an amastigote following infection of a macrophage, GFP-ATG8 has an initial cytosolic distribution (1 h p.i., one parasite visualised), associates with multiple autophagosomes at peak differentiation (24 h, one parasite visualised) and is subsequently found in the cytosol (48 h, two parasites visualised). Scale bar is 10 μm.