Comparative studies of the low-resolution structure of two p23 co-chaperones for Hsp90 identified in Plasmodium falciparum genome.

The p23 proteins are small acidic proteins that aid the functional cycle of the Hsp90 molecular chaperone. Such co-chaperone acts by temporarily inhibiting the ATPase activity of Hsp90 and exhibits intrinsic chaperone activity, suggesting independent roles. A search for p23 in the Plasmodium falciparum genome led to the identification of two putative proteins showing 13% identity to each other and approximately 20% identity to human p23. To understand the presence of two p23 proteins in this organism, we generated recombinant p23 proteins (Pfp23A and Pfp23B) and investigated their structure and function. The proteins presented some similarities and dissimilarities in structural contents and showed different chemical and thermal stabilities, with Pfp23A being more stable than Pfp23B, suggesting that these proteins may present different functions in this organism. Both Pfp23 proteins behaved as elongated monomers in solution and were capable of preventing the thermal-induced aggregation of model client proteins with different efficiencies. Finally, the Pfp23 proteins inhibited the ATPase activity of recombinant P. falciparum Hsp90 (PfHsp90). These results validate the studied proteins as p23 proteins and co-chaperones of PfHsp90.