Molecular analysis of Plasmodium falciparum co-chaperone Aha1 supports its interaction with and regulation of Hsp90 in the malaria parasite

Int J Biochem Cell Biol. 2012 Jan;44(1):233-45. doi: 10.1016/j.biocel.2011.10.021. Epub 2011 Nov 11.


The recent recognition of Plasmodium falciparum Hsp90 (PfHsp90) as a promising anti-malaria drug target has sparked interest in identifying factors that regulate its function and drug-interaction. Co-chaperones are well-known regulators of Hsp90's chaperone function, and certain members have been implicated in conferring protection against lethal cellular effects of Hsp90-specific inhibitors. In this context, studies on PfHsp90's co-chaperones are imperative to gain insight into the regulation of the chaperone in the malaria parasite. In this study, a putative co-chaperone P. falciparum Aha1 (PfAha1) was identified and investigated for its interaction and regulation of PfHsp90. A previous genome-wide yeast two-hybrid study failed to identify PfAha1's association with PfHsp90, which prompted us to use a directed assay to investigate their interaction. PfAha1 was shown to interact with PfHsp90 via the in vivo split-ubiquitin assay and the association was confirmed in vitro by GST pull-down experiments. The GST pull-down assay further revealed PfAha1's interaction with PfHsp90 to be dependent on MgCl(2) and ATP, and was competed by co-chaperone Pfp23 that binds PfHsp90 under the same condition. In addition, the PfHsp90-PfAha1 complex was found to be sensitive to disruption by high salt, indicating a polar interaction between them. Using bio-computational modelling coupled with site-directed mutagenesis, the polar residue N108 in PfAha1 was found to be strategically located and essential for PfHsp90 interaction. The functional significance of PfAha1's interaction was clearly that of exerting a stimulatory effect on the ATPase activity of PfHsp90, likely to be essential for promoting the activation of PfHsp90's client proteins.

MeSH terms

  • Adenosine Triphosphatases / metabolism
  • Amino Acid Sequence
  • Animals
  • Genome, Protozoan
  • HSP90 Heat-Shock Proteins / chemistry
  • HSP90 Heat-Shock Proteins / genetics*
  • HSP90 Heat-Shock Proteins / metabolism*
  • Humans
  • Models, Molecular
  • Molecular Chaperones / chemistry
  • Molecular Chaperones / genetics*
  • Molecular Chaperones / metabolism*
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Plasmodium falciparum / genetics*
  • Plasmodium falciparum / metabolism*
  • Sequence Alignment


  • HSP90 Heat-Shock Proteins
  • Molecular Chaperones
  • Adenosine Triphosphatases