A novel role for 100 kD heat shock proteins in the parasite Leishmania donovani.

Heat shock proteins of the 100 kD family have been known to confer general stress tolerance in yeast and plants. Several protozoan parasites possess genes for Hsp100 proteins. In Leishmania species the protein is expressed under heat stress and during the mammalian stage, the amastigote. We show here that replacement of the clpB gene which encodes Hsp100 does not affect thermotolerance or general viability in Leishmania donovani insect stages (promastigotes) nor in axenically cultured mammalian stages (amastigotes). However, its expression is required for normal development of the parasite inside mammalian host cells. Hsp100 appears to function as an antagonist of amastigote-to-promastigote differentiation and a promoter of full amastigote development.