Abstract

Hsp90 is important for normal growth and development in eukaryotes. Together with Hsp70 and other accessory proteins, Hsp90 not only helps newly synthesized proteins to fold but also regulates activities of transcription factors and protein kinases. Although the gene coding for heat shock protein 90 from Plasmodium falciparum (PfHsp90) has been characterized previously, there is very little known regarding its function in the parasite. We have analyzed PfHsp90 complexes and addressed its role in parasite life cycle using Geldanamycin (GA), a drug known to interfere with Hsp90 function. Sedimentation analysis and size exclusion chromatography showed PfHsp90 to be in 11 s(20,(w)) complexes of approximately 300 kDa in size. Similar to the hetero-oligomeric complexes of Hsp90 in mammals, PfHsp70 was found to be present in PfHsp90 complexes. Homology modeling revealed a putative GA-binding pocket at the amino terminus of PfHsp90. The addition of GA inhibited parasite growth with LD(50) of 0.2 microm. GA inhibited parasite growth by arresting transition from Ring to trophozoite. Transition from trophozoite to schizonts and reinvasion of new erythrocytes were less significantly affected. While inducing the synthesis of PfHsp70 and PfHsp90, GA did not significantly alter the pattern of newly synthesized proteins. Pre-exposure to heat shock attenuated GA-mediated growth inhibition, suggesting the involvement of heat shock proteins. Specificity of GA action on PfHsp90 was evident from selective inhibition of PfHsp90 phosphorylation in GA-treated cultures. In addition to suggesting an essential role for PfHsp90 during parasite growth, our results highlight PfHsp90 as a potential drug target to control malaria.

Highlights

  • Known to be expressed by the parasite during the intraerythrocytic stages in the vertebrate host [2,3,4]

  • The gene coding for heat shock protein 90 from Plasmodium falciparum (PfHsp90) has been characterized previously, there is very little known regarding its function in the parasite

  • We have examined the complexes of PfHsp90 and analyzed its role in parasite growth in human erythrocytes using GA

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Summary

Introduction

Known to be expressed by the parasite during the intraerythrocytic stages in the vertebrate host [2,3,4] These heat shock proteins share significant homologies with their mammalian counterparts, there is very limited information available regarding their functional roles in parasite development. We have focused our study on the role of parasite-heat shock protein 90 expressed during erythrocytic cycle in humans. 1) Together with Hsp and Hsp, Hsp helps newly synthesized proteins to fold and 2) it helps modulate the activities of transcription factors (steroid hormone receptors and nuclear receptors) and protein kinases (8 –10) The latter activity of Hsp puts it at the center stage of signal transduction events, crucial for cell survival and growth.

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