Plasmodium falciparum Hep1 Is Required to Prevent the Self Aggregation of PfHsp70-3

Presequence translocase-associated motor subunits of the mitochondrial protein import apparatus are dual-targeted to mitochondria and plastids

The import and assembly of most of the mitochondrial proteome is regulated by protein translocases located within the mitochondrial membranes. The Presequence Translocase-Associated Motor (PAM) complex powers the translocation of proteins across the inner membrane and consists of Hsp70, the J-domain containing co-chaperones, Pam16 and Pam18, and their associated proteins Tim15 and Mge1. In Arabidopsis, multiple orthologues of Pam16, Pam18, Tim15 and Mge1 have been identified and a mitochondrial localization has been confirmed for most. As the localization of Pam18-1 has yet to be determined and a plastid localization has been observed for homologues of Tim15 and Mge1, we carried out a comprehensive targeting analysis of all PAM complex orthologues using multiple in vitro and in vivo methods. We found that, Pam16 was exclusively targeted to the mitochondria, but Pam18 orthologues could be targeted to both the mitochondria and plastids, as observed for the PAM complex interacting partner proteins Tim15 and Mge1.

Heat Shock Proteins as Targets for Novel Antimalarial Drug Discovery

Plasmodium falciparum, the parasitic agent that is responsible for a severe and dangerous form of human malaria, has a history of long years of cohabitation with human beings with attendant negative consequences. While there have been some gains in the fight against malaria through the application of various control measures and the use of chemotherapeutic agents, and despite the global decline in malaria cases and associated deaths, the continual search for new and effective therapeutic agents is key to achieving sustainable development goals. An important parasite survival strategy, which is also of serious concern to the scientific community, is the rate at which the parasites continually develop resistance to drugs. Among the key players in the parasite's ability to develop resistance, maintain cellular integrity, and survives within an unusual environment of the red blood cells are the molecular chaperones of the heat shock proteins (HSP) family. HSPs constitute a novel avenue for antimalarial drug discovery and by exploring their ubiquitous nature and multifunctional activities, they may be suitable targets for the discovery of multi-targets antimalarial drugs, needed to fight incessant drug resistance. In this chapter, features of selected families of plasmodial HSPs that can be exploited in drug discovery are presented. Also, known applications of HSPs in small molecule screening, their potential usefulness in high throughput drug screening, as well as possible challenges are highlighted.

The Role of Hsp70s in the Development and Pathogenicity of Plasmodium falciparum

The main agent of human malaria, the protozoa, Plasmodium falciparum is known to infect liver cells, subsequently invading the host erythrocyte, leading to the manifestation of clinical outcomes of the disease. As part of its survival in the human host, P. falciparum employs several heat shock protein (Hsp) families whose primary purpose is to ensure cytoprotection through their molecular chaperone role. The parasite expresses six Hsp70s that localise to various subcellular organelles of the parasite, with one, PfHsp70-x, being exported to the infected human erythrocyte. The role of these Hsp70s in the survival and pathogenicity of malaria has received immense research attention. Several studies have reported on their structure-function features, network partnerships, and elucidation of their potential substrates. Apart from their role in cytoprotection and pathogenicity, Hsp70s are implicated in antimalarial drug resistance. As such, they are deemed potential antimalarial drug candidates, especially suited for co-targeting in combination therapies. In addition, Hsp70 is implicated in host immune modulation. The current report highlights the various structure-function features of these proteins, their roles in the development of malaria, current and prospective efforts being employed towards targeting them in malaria intervention efforts.

Structural, thermodynamic and functional studies of human 71 kDa heat shock cognate protein (HSPA8/hHsc70)

Human 71 kDa heat shock cognate protein (HSPA8, also known as Hsc70, Hsp70-8, Hsc71, Hsp71 or Hsp73) is a constitutively expressed chaperone that is critical for cell proteostasis. In the cytosol, HSPA8 plays a pivotal role in folding and refolding, facilitates protein trafficking across membranes and targets proteins for degradation, among other functions. Here, we report an in solution study of recombinant HSPA8 (rHSPA8) using a variety of biophysical and biochemical approaches. rHSPA8 shares several structural and functional similarities with others human Hsp70s. It has two domains with different stabilities and interacts with adenosine nucleotides with dissociation constants in the low micromolar range, which were higher in the presence of Mg²⁺. rHSPA8 showed lower ATPase activity than its homolog HSPA5/hGrp78/hBiP, but it was 4-fold greater than that of recombinant HSPA1A/hHsp70-1A, with which it is 86% identical. Small angle X-ray scattering indicated that rHSPA8 behaved as an elongated monomeric protein in solution with dimensions similar to those observed for HSPA1A. In addition, rHSPA8 showed structural flexibility between its compacted and extended conformations. The data also indicated that HSPA8 has capacity in preventing the aggregation of model client proteins. The present study expands the understanding of the structure and activity of this chaperone and aligns with the idea that human homologous Hsp70s have divergent functions.

New insights on human Hsp70-escort protein 1: Chaperone activity, interaction with liposomes, cellular localizations and HSPA's self-assemblies remodeling

The 70 kDa heat shock proteins (Hsp70) are prone to self-assembly under thermal stress conditions, forming supramolecular assemblies (SMA), what may have detrimental consequences for cellular viability. In mitochondria, the cochaperone Hsp70-escort protein 1 (Hep1) maintains mitochondrial Hsp70 (mtHsp70) in a soluble and functional state, contributing to preserving proteostasis. Here we investigated the interaction between human Hep1 (hHep1) and HSPA9 (human mtHsp70) or HSPA1A (Hsp70-1A) in monomeric and thermic SMA states to unveil further information about the involved mechanisms. hHep1 was capable of blocking the formation of HSPA SMAs under a thermic treatment and stimulated HSPA ATPase activity in both monomeric and preformed SMA. The interaction of hHep1 with both monomeric and SMA HSPAs displayed a stoichiometric ratio close to 1, suggesting that hHep1 has access to most protomers within the SMA. Interestingly, hHep1 remodeled HSPA9 and HSPA1A SMAs into smaller forms. Furthermore, hHep1 was detected in the mitochondria and nucleus of cells transfected with the respective coding DNA and interacted with liposomes resembling mitochondrial membranes. Altogether, these new features reinforce that hHep1 act as a "chaperone for a chaperone", which may play a critical role in cellular proteostasis.

Proteomic analysis of microparticles isolated from malaria positive blood samples

Background

Malaria continues to be a great public health concern due to the significant mortality and morbidity associated with the disease especially in developing countries. Microparticles (MPs), also called plasma membrane derived extracellular vesicles (PMEVs) are subcellular structures that are generated when they bud off the plasma membrane. They can be found in healthy individuals but the numbers tend to increase in pathological conditions including malaria. Although, various studies have been carried out on the protein content of specific cellular derived MPs, there seems to be paucity of information on the protein content of circulating MPs in malaria and their association with the various signs and symptoms of the disease. The aim of this study was therefore to carry out proteomic analyses of MPs isolated from malaria positive samples and compare them with proteins of MPs from malaria parasite culture supernatant and healthy controls in order to ascertain the role of MPs in malaria infection.

Methods

Plasma samples were obtained from forty-three (43) malaria diagnosed patients (cases) and ten (10) healthy individuals (controls). Malaria parasite culture supernatant was obtained from our laboratory and MPs were isolated from them and confirmed using flow cytometry. 2D LC-MS was done to obtain their protein content. Resultant data were analyzed using SPSS Ver. 21.0 statistical software, Kruskal Wallis test and Spearman’s correlation coefficient r.

Results

In all, 1806 proteins were isolated from the samples. The MPs from malaria positive samples recorded 1729 proteins, those from culture supernatant were 333 while the control samples recorded 234 proteins. The mean number of proteins in MPs of malaria positive samples was significantly higher than that in the control samples. Significantly, higher quantities of haemoglobin subunits were seen in MPs from malaria samples and culture supernatant compared to control samples.

Conclusion

A great number of proteins were observed to be carried in the microparticles (MPs) from malaria samples and culture supernatant compared to controls. The greater loss of haemoglobin from erythrocytes via MPs from malaria patients could serve as the initiation and progression of anaemia in P.falciparum infection. Also while some proteins were upregulated in circulating MPs in malaria samples, others were down regulated.