Preparation of Parasite Protein Extracts and Western Blot Analysis

Abstract

In order to prepare protein extracts of Plasmodium falciparum blood stages for western blot analysis, infected red blood cells (iRBC) need to be separated from uninfected red blood cells (uRBC) which make up the bulk of the parasite culture. Depending on the localisation of the parasite protein of interest, different methods are available to achieve this. If the protein is present within the parasite or is attached to a cellular structure of the iRBC cell, saponin can be used. This reagent lyses the membranes of infected and uninfected erythrocytes, the Maurer´s clefts (vesicular structures in the iRBC) and the parasitophorous vacuole membrane containing the parasite but leaves the parasite plasma membrane intact, providing a convenient procedure to isolate intact parasites without uRBCs. However, this method has the disadvantage that the host cell cytosol and the parasitophorous vacuole (PV) content of iRBCs are lost. If this has to be avoided, it is possible to use a Percoll gradient to separate intact iRBCs from uRBCs. Sequential treatment with Tetanolysin and saponin can then be used to selectively release the iRBC cytosol and the PV content from the parasite. These selective lysis methods are also suitable to determine the subcellular localisation of a protein of interest.