Comparison of protein expression pattern between the Plasmodium falciparum chloroquine-resistant RKL9 and chloroquine-sensitive MRC2 strains

OBJECTIVE: The objective of this study was to compare the protein expression patterns of Plasmodium falciparum extracellular and intracellular proteins separated by two-dimensional electrophoresis (2-DE) from the chloroquine-sensitive (CQS) MRC2 strain and chloroquine-resistant (CQR) RKL9 strain. Materials and Methods: Both the extracellular protein (ECP) and intracellular protein (ICP) were extracted and solubilized. The proteins were separated by 2-DE, first based on their charges using isoelectric focusing and then their sizes by electrophoresis. The separated protein spots were detected by silver staining, and further, the protein spot density was analyzed by an image analysis software. RESULTS: 2-DE separated the proteins extracted from the CQS and CQR strains based on their differentially expressed protein patterns. EXTRACELLULAR PROTEIN ANALYSIS: A total of 109 and 77 protein spots were detected by image analysis of ECP extracted from MRC2 and RKL9 strains, respectively. There was a marked reduction in protein expression pattern in the CQR strain when compared with the CQS strain. Interestingly, 50 and 18 protein spots were uniquely expressed in MRC2 and RKL9 strains, respectively. When MRC2 strain-expressed proteins were taken as the control, 12 upregulated and 14 downregulated protein spots were observed in the RKL9 strain-extracted proteins. INTRACELLULAR PROTEIN ANALYSIS: ICP extracted from MRC2 and RKL9 strains showed 187 and 199 protein spots by an image analysis software, and a small enhancement of protein expression was measured when comparing the CQR strain with CQS strain. There were 67 and 79 unique protein spots detected in MRC2 and RKL9 strains, respectively. A total of 120 protein spots were similar when MRC2 proteins were taken as the control; among these protein spots, 40 upregulated and 22 downregulated protein spots were detected in RKL9 strain-expressed protein. CONCLUSIONS: Both these unique and matched protein spots might be molecularly potent drug targets for chloroquine resistance in P. falciparum. Further identification of these proteins by mass spectrometry/peptide sequencing is essential to clearly understand the mechanism of resistance.