Induction and localization of Plasmodium falciparum stress proteins related to the heat shock protein 70 family

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Abstract

Induction of heat shock-related stress proteins Pfhsp and Pfgrp, similar in sequence to hsp70 (heat shock protein) and grp78 (glucose-regulated protein), respectively, was studied in culture-derived parasite Plasmodium falciparum. Elevation in temperature from 26°C to 37°C and higher caused significant induction of Pfhsp with a moderate effect on the synthesis of Pfgrp also. Synthesis of Pfgrp, however, was not induced by partial glucose deprivation. On the contrary, lack of glucose in the medium resulted in cessation of protein synthesis in the parasites. Other known inducers of grp synthesis in mammalian cells, i.e., calcium ionophore A23187 and inhibitors of glycosylation (tunicamycin, 2-deoxy glucose) were also without any apparent effect on the synthesis of Pfgrp. Heat shock-induced responses were transient in nature: removal of stress caused repression of these responses. The effect of glucose deprivation was only partially reversible with better recovery if parasites were subjected to glucose starvation at 26°C than at 37°C. Northern blot analysis and in vitro translation of mRNA revealed a parallel increase in the levels of mRNA for Pfhsp upon heat shock. Immuno-gold electron microscopy with cultured parasites revealed nuclear location of Pfhsp and primarily cytoplasmic (probably endoplasmic reticulum) location of Pfgrp. These findings suggest that SDEL (carboxy terminal sequence of Pfgrp) might play a similar role in the cellular localization of Pfgrp as does the sequence KDEL in mammalian cells and HDEL in yeast.

Keywords

Heat shock protein
Stress protein
Malaria
Plasmodium falciparum
Endoplasmic reticulum
Host-parasite adaptation

Abbreviations

hsp
heat shock protein
grp
glucose-regulated protein
Pfhsp
Plasmodium falciparum hsp70
Pfgrp
P. falciparum grp78
SDS-PAGE
sodium dodecyl sulfate-polyacrylamide gel electrophoresis
EM
electron microscopy
ER
endoplasmic reticulum
TCA
trichloroacetic acid

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