Structural studies of the Activator of HSP90 ATPase (Aha) co-chaperone isoforms in Plasmodium falciparum in complex with the HSP90 chaperone and characterization of their cellular roles

• Grant number: 21/02289-4
• Support Opportunities: Scholarships in Brazil - Post-Doctorate
• Effective date (Start): November 01, 2021
• Effective date (End): January 15, 2023
• Field of knowledge: Biological Sciences - Biochemistry - Chemistry of Macromolecules
• Principal Investigator: Julio Cesar Borges
• Grantee: Thiago Vargas Seraphim
• Host Institution: Instituto de Química de São Carlos (IQSC). Universidade de São Paulo (USP). São Carlos , SP, Brazil
• Associated research grant: 17/26131-5 - The chaperome: study of the relationship of the structure of its components and the maintenance of proteostasis, AP.TEM

Abstract

The HSP90 molecular chaperone is a central player in the maintenance of proteostasis, being essential to cell viability in normal and stress conditions. Abnormal HSP90 activity contributes to the development of several diseases, such as cancer, neurodegeneration, among others. This chaperone also plays a critical role in the proteostasis maintenance in protozoa and the unbalancing of its functions leads to the disruption of parasites life cycle. HSP90 binds to hydrophobic regions of client proteins, stabilizing them, and its biological activity depends on ATP binding and hydrolysis, which directs large conformational changes in its functional cycle. Auxiliary proteins, dubbed co-chaperones, bind to HSP90 and assist the directionality of its conformational changes, regulating them. One can highlight Aha co-chaperones, which stabilize HSP90 in a catalytically active conformation, stimulating the HSP90 ATPase activity by several fold. Four types of Aha co-chaperones, numbered here from 1 to 4, displaying different structural organizations are known to the present. Aha1 was found in humans whereas Aha1 and Aha3 were found in yeast; Aha2 was found in apicomplexan organisms and Aha4 was found in Plasmodium and non-metazoan eukaryotes. The most well-characterized Aha co-chaperones are Aha1 and Aha3, in contrast to the poor knowledge about Aha2 and Aha4. In this context, this project aims to characterize the underlying mechanism of HSP90 stimulation by Aha2 and Aha4 from P. falciparum, as well as their cellular roles. To achieve these aims, we propose to map interacting interfaces among these proteins, investigate PfHSP90 conformational changes upon PfAha2 and PfAha4 binding and the structure of PfAha2-PfHSP90 and PfAha4-PfHSP90 complexes. In addition, we aim to determine the role of these co-chaperones in the cell physiology of P. falciparum, identifying their cellular localization, phenotypic expressions associated to the downregulation of their cellular levels and their involvement in cellular pathways. The expectation of a successful accomplishment of this post-doctoral project are based on the team experience in the proposed topic and in most of the proposed techniques, in the availability of recombinant proteins for biophysical and structural studies, as well as on the preliminary data available. Although challenging, expected outcomes from this project have the potential to generate knowledge of high impact in the field, leading to a detailed description (and possibly to a novel classification for these group of proteins) of unprecedented molecular mechanisms through which PfAha2 and PfAha4 co-chaperones operate in the cell, and to potentially contribute to the development of novel selective antimalarial therapies. (AU)