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HSP90 is an abundantly and ubiquitously expressed heat shock protein. It is understood to exist in two principal
forms α and β, which share 85% sequence amino acid
homology. The two isoforms of Hsp90 are expressed in
the cytosolic compartment (1). Despite the similarities,
HSP90α exists predominantly as a homodimer while
HSP90β exists mainly as a monomer.(2) From a functional
perspective, hsp90 participates in the folding, assembly,
maturation, and stabilization of specific proteins as an
integral component of a chaperone complex. (3-6)
Furthermore, Hsp90 is highly conserved between species;
having 60% and 78% amino acid similarity between
mammalian and the corresponding yeast and Drosophila
proteins, respectively.
Hsp90 is a highly conserved and essential stress protein
that is expressed in all eukaryotic cells. Despite its label
of being a heat-shock protein, hsp90 is one of the most highly
expressed proteins in unstressed cells (12% of cytosolic
protein). It carries out a number of housekeeping functions 
including controlling the activity, turnover, and trafficking of
a variety of proteins. Most of the hsp90-regulated proteins
that have been discovered to date are involved in cell
signaling (7-8). The number of proteins now know to interact
with Hsp90 is about 100. Target proteins include the kinases
v-Src, Wee1, and c-Raf, transcriptional regulators such as p53
and steroid receptors, and the polymerases of the hepatitis B
virus and telomerase.5 When bound to ATP, Hsp90 interacts
with co-chaperones Cdc37, p23, and an assortment of
immunophilin-like proteins, forming a complex that stabilizes
and protects target proteins from proteasomal degradation.
In most cases, hsp90-interacting proteins have been shown to
co-precipitate with hsp90 when carrying out immune
adsorption studies, and to exist in cytosolic heterocomplexes
with it. In a number of cases, variations in hsp90 expression
or hsp90 mutation has been shown to degrade signaling
function via the protein or to impair a specific function of the
protein (such as steroid binding, kinase activity) in vivo.
Ansamycin antibiotics, such as geldanamycin and radicicol,
inhibit hsp90 function (9).
Recently, Prof. Tatu’s laboratory has shown the importance
of Hsp90 in parasite growth. They have shown that inhibition
of P. Falciparum Hsp90 (PfHsp90), blocks the erythrocytic
cycle by inhibiting stage transformation, leading to inhibition
of parasite growth (10, 11).