The heat URLanizing protein (Hop) is important in modulating the activity and co-interaction of two chaperones: heat shock protein 90 and 70  ( Hsp90 and Hsp70  ). Recent research suggests that Plasmodium falciparum Hop (PfHop), PfHsp90 and PfHsp70  form a complex in the trophozoite infective stage. However, there has been little computational research on the malarial Hop protein in complex with other malarial Hsps. Using in silico characterization of PfHop , this work showed that individual domains of Hop are evolving at different rates within the protein.  Homology modeling of PfHop , and of human Hop (HsHop ) in complex with its own cytosolic Hsp90 and Hsp70 C-terminal peptide partners , indicated high conservation of the Hop concave TPR sites bound to the C-terminal motifs of partner proteins. Further, for the first time, we identified two additional binding sites between Hop and Hsp90 which are distinctly less conserved between human and malaria parasite. These two sites are located on the convex surface of Hop TPR2  and involved in interactions with  Hsp90 middle and C-terminal domains. Motif analysis was combined with phylogenetic trees and structural mapping to investigate the evolutionary conservation of important structural and functional sites of Hop. Statistical coupling analysis identified several sectors of coevolving residues in Hop. The convex sites of interaction between Hop TPR2 and Hsp90 middle and C-terminal domains were found to be part of separately coevolving sectors. This provides further evidence that these convex interaction sites are important to complex formation with Hsp90, and are thus potential sites for inhibitor design (in addition to the concave sites which have been the focus of previous efforts) . Further the convex sites are less conserved than the concave sites, which make their potential for malarial inhibitor design extremely attractive .
The heat URLanizing protein (Hop) is important in modulating the activity and co-interaction of two chaperones: heat shock protein 70 and 90 ( Hsp70 and Hsp90 ). Recent research suggested that Plasmodium falciparum Hop (PfHop), PfHsp70 and PfHsp90 form a complex in the trophozoite infective stage. However, there has been little computational research on the malarial Hop protein in complex with other malarial Hsps. Using in silico characterization of the protein , this work showed that individual domains of Hop are evolving at different rates within the protein. Differences between human Hop (HsHop) and PfHop were identified by motif analysis. Homology modeling of PfHop and HsHop in complex with their own cytosolic Hsp90 and Hsp70 C-terminal peptide partners indicated excellent conservation of the Hop concave TPR sites bound to the C-terminal motifs of partner proteins. Further, we analyzed additional binding sites between Hop and Hsp90 , and showed, for the first time, that they are distinctly less conserved between human and malaria parasite. These sites are located on the convex surface of Hop TPR2 , and involved in interactions with the Hsp90 middle domain. Since the convex sites are less conserved than the concave sites, it makes their potential for malarial inhibitor design extremely attractive (as opposed to the concave sites which have been the focus of previous efforts) .
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