Structures of Brucella ovis leucine-, isoleucine-, valine-, threonine- and alanine-binding protein reveal a conformationally flexible peptide-binding cavity.

Brucella ovis is an etiologic agent of ovine epididymitis and brucellosis that causes global devastation in sheep, rams, goats, small ruminants and deer. There are no cost-effective methods for the worldwide eradication of ovine brucellosis. B. ovis and other protein targets from various Brucella species are currently in the pipeline for high-throughput structural analysis at the Seattle Structural Genomics Center for Infectious Disease (SSGCID), with the aim of identifying new therapeutic targets. Furthermore, the wealth of structures generated are effective tools for teaching scientific communication, structural science and biochemistry. One of these structures, B. ovis leucine-, isoleucine-, valine-, threonine- and alanine-binding protein (BoLBP), is a putative periplasmic amino acid-binding protein. BoLBP shares less than 29% sequence identity with any other structure in the Protein Data Bank. The production, crystallization and high-resolution structures of BoLBP are reported. BoLBP is a prototypical bacterial periplasmic amino acid-binding protein with the characteristic Venus flytrap topology of two globular domains encapsulating a large central cavity containing the peptide-binding region. The central cavity contains small molecules usurped from the crystallization milieu. The reported structures reveal the conformational flexibility of the central cavity in the absence of bound peptides. The structural similarity to other LBPs can be exploited to accelerate drug repurposing.

Swapping the linkers of canonical Hsp70 and Hsp110 chaperones compromises both self-association and client selection.

Plasmodium falciparum heat shock protein 70-1 (PfHsp70-1) and PfHsp70-z are essential cytosol localised chaperones of the malaria parasite. The two chaperones functionally interact to drive folding of several parasite proteins. While PfHsp70-1 is regarded as a canonical Hsp70 chaperone, PfHsp70-z belongs to the Hsp110 subcluster. One of the distinctive features of PfHsp70-z is its unique linker segment which delineates it from canonical Hsp70. In the current study, we elucidated the role of the linker in regulating Hsp70 self-association and client selection. Using recombinant forms of PfHsp70-1, PfHsp70-z and E. coli Hsp70 (DnaK) and their respective linker switch mutants we investigated self-association of the chaperones using surface plasmon resonance (SPR) analysis. The effect of the changes on client selectivity was investigated on DnaK and its mutant through co-affinity chromatography coupled to LC-MS analysis. Our findings demonstrated that the linker is important for both Hsp70 self-association and client binding.

Insertion of GGMP repeat residues of Plasmodium falciparum Hsp70-1 in the lid of DnaK adversely impacts client recognition.

Although Hsp70 is a conserved molecular chaperone, it exhibits some degree of functional specialisation across species. Features of Hsp70 regulating its functional specialisation remain to be fully established. We previously demonstrated that E. coli Hsp70 (DnaK) exhibits functional features that distinguishes it from PfHsp70-1, a canonical cytosolic Hsp70 of Plasmodium falciparum. One of the defining features of PfHsp70-1 is that it possesses GGMP repeat residues located in its C-terminal lid segment, while DnaK lacks this motif. Previously, we demonstrated that the insertion of GGMP repeat residues of PfHsp70-1 into E. coli DnaK abrogates the chaperone activity of DnaK. However, the role of the GGMP motif in regulating Hsp70 function remains to be fully understood. To explore the function of this motif, we expressed recombinant forms of wild type DnaK and its GGMP insertion motif, DnaK-G and systematically characterised the structure-function features of the two proteins using in silico analysis, biophysical approaches and an in cellulo complementation assay. Our findings demonstrated that the GGMP inserted in DnaK compromised various functional features such as nucleotide binding, allostery, substrate binding affinity and cellular proteome client selectivity. These findings thus, highlight the GGMP motif of Hsp70 as an important functional module.

Proteomic Profiling in Patients With Peripartum Cardiomyopathy: A Biomarker Study of the ESC EORP PPCM Registry.

BACKGROUND: Peripartum cardiomyopathy (PPCM) remains an important cause of maternal morbidity and mortality globally. The pathophysiology remains incompletely understood, and the diagnosis is often missed or delayed. OBJECTIVES: This study explored the serum proteome profile of patients with newly diagnosed PPCM, as compared with matched healthy postpartum mothers, to unravel novel protein biomarkers that would further an understanding of the pathogenesis of PPCM and improve diagnostic precision. METHODS: Study investigators performed untargeted serum proteome profiling using data-independent acquisition-based label-free quantitative liquid chromatography-tandem mass spectrometry on 84 patients with PPCM, as compared with 29 postpartum healthy controls (HCs). Significant changes in protein intensities were determined with nonpaired Student's t-tests and were further classified by using the Boruta algorithm. The proteins' diagnostic performance was evaluated by area under the curve (AUC) and validated using the 10-fold cross-validation. RESULTS: Patients with PPCM presented with a mean left ventricular ejection fraction of 33.5% ± 9.3% vs 57.0% ± 8.8% in HCs (P < 0.001). Study investigators identified 15 differentially up-regulated and 14 down-regulated proteins in patients with PPCM compared with HCs. Seven of these proteins were recognized as significant by the Boruta algorithm. The combination of adiponectin, quiescin sulfhydryl oxidase 1, inter-α-trypsin inhibitor heavy chain, and N-terminal pro-B-type natriuretic peptide had the best diagnostic precision (AUC: 0.90; 95% CI: 0.84-0.96) to distinguish patients with PPCM from HCs. CONCLUSIONS: Salient biologic themes related to immune response proteins, inflammation, fibrosis, angiogenesis, apoptosis, and coagulation were predominant in patients with PPCM compared with HCs. These newly identified proteins warrant further evaluation to establish their role in the pathogenesis of PPCM and potential use as diagnostic markers.

Heat Shock Proteins: Potential Modulators and Candidate Biomarkers of Peripartum Cardiomyopathy.

Peripartum cardiomyopathy (PPCM) is a potentially life-threatening condition in which heart failure and systolic dysfunction occur late in pregnancy or within months following delivery. To date, no reliable biomarkers or therapeutic interventions for the condition exist, thus necessitating an urgent need for identification of novel PPCM drug targets and candidate biomarkers. Leads for novel treatments and biomarkers are therefore being investigated worldwide. Pregnancy is generally accompanied by dramatic hemodynamic changes, including a reduced afterload and a 50% increase in cardiac output. These increased cardiac stresses during pregnancy potentially impair protein folding processes within the cardiac tissue. The accumulation of misfolded proteins results in increased toxicity and cardiac insults that trigger heart failure. Under stress conditions, molecular chaperones such as heat shock proteins (Hsps) play crucial roles in maintaining cellular proteostasis. Here, we critically assess the potential role of Hsps in PPCM. We further predict specific associations between the Hsp types Hsp70, Hsp90 and small Hsps with several proteins implicated in PPCM pathophysiology. Furthermore, we explore the possibility of select Hsps as novel candidate PPCM biomarkers and drug targets. A better understanding of how these Hsps modulate PPCM pathogenesis holds promise in improving treatment, prognosis and management of the condition, and possibly other forms of acute heart failure.

Supporting data on characterisation of linker switch mutants of Plasmodium falciparum heat shock protein 110 and canonical Hsp70.

Here, we present data on characterisation of the linker of Plasmodium falciparum Hsp110 (PfHsp70-z) relative to the linker of canonical Hsp70s in support of a co-published article [1]. The linker of PfHsp70-z was switched with that of canonical Hsp70s, represented by PfHsp70-1 (cytosolic counterpart of PfHsp70-z) and E. coli Hsp70/DnaK. The datasets represent comparative analyses of PfHsp70-z, PfHsp70-1, and E. coli DnaK, relative to their linker switch mutants; PfHsp70-zLS, PfHsp70-1LS, DnaKLS, respectively. Intrinsic and extrinsic fluorescence spectroscopic analyses were employed to elucidate effects of the mutations on the structural features of the proteins. The structural conformations of the proteins were analysed in the absence as well as presence of nucleotides. In addition, stability of the proteins to stress (pH changes and urea) was also determined. Surface plasmon resonance (SPR) was employed to determine affinity of the proteins for ATP. The relative affinities of PfHsp70-z and PfHsp70-1 for the parasite cytosol localised, J domain co-chaperone, PfHsp40, was determined by SPR analysis. The effect of the linker of PfHsp70-z on the interaction of DnaKLS with DnaJ (a co-chaperone of DnaK), was similarly determined. These data could be used for future investigations involving protein-protein/ligand interactions as described in [1]. The raw data obtained using the various techniques here described are hosted in the Mendeley Data repository at [2].

Characterisation of a unique linker segment of the Plasmodium falciparum cytosol localised Hsp110 chaperone.

Plasmodium falciparum expresses two essential cytosol localised chaperones; PfHsp70-1 and PfHsp70-z. PfHsp70-z (Hsp110 homologue) is thought to facilitate nucleotide exchange function of PfHsp70-1. PfHsp70-1 is a refoldase, while PfHsp70-z is restricted to holdase chaperone function. The structural features delineating functional specialisation of these chaperones remain unknown. Notably, PfHsp70-z possesses a unique linker segment which could account for its distinct functions. Using recombinant forms of PfHsp70-1, PfHsp70-z and E. coli Hsp70 (DnaK) as well as their linker switch mutant forms, we explored the effects of the linker mutations by conducting several assays such as circular dichroism, intrinsic and extrinsic fluorescence coupled to biochemical and in cellular analyses. Our findings demonstrate that the linker of PfHsp70-z modulates global conformation of the chaperone, regulating several functions such as client protein binding, chaperone- and ATPase activities. In addition, as opposed to the flexible linker of PfHsp70-1, the PfHsp70-z linker is rigid, thus regulating its notable thermal stability, making it an effective stress buffer. Our findings suggest a crucial role for the linker in streamlining the functions of these two chaperones. The findings further explain how these distinct chaperones cooperate to ensure survival of P. falciparum particularly under the stressful human host environment.

Mutation of GGMP Repeat Segments of Plasmodium falciparum Hsp70-1 Compromises Chaperone Function and Hop Co-Chaperone Binding.

Parasitic organisms especially those of the Apicomplexan phylum, harbour a cytosol localised canonical Hsp70 chaperone. One of the defining features of this protein is the presence of GGMP repeat residues sandwiched between α-helical lid and C-terminal EEVD motif. The role of the GGMP repeats of Hsp70s remains unknown. In the current study, we introduced GGMP mutations in the cytosol localised Hsp70-1 of Plasmodium falciparum (PfHsp70-1) and a chimeric protein (KPf), constituted by the ATPase domain of E. coli DnaK fused to the C-terminal substrate binding domain of PfHsp70-1. A complementation assay conducted using E. coli dnaK756 cells demonstrated that the GGMP motif was essential for chaperone function of the chimeric protein, KPf. Interestingly, insertion of GGMP motif of PfHsp70-1 into DnaK led to a lethal phenotype in E. coli dnaK756 cells exposed to elevated growth temperature. Using biochemical and biophysical assays, we established that the GGMP motif accounts for the elevated basal ATPase activity of PfHsp70-1. Furthermore, we demonstrated that this motif is important for interaction of the chaperone with peptide substrate and a co-chaperone, PfHop. Our findings suggest that the GGMP may account for both the specialised chaperone function and reportedly high catalytic efficiency of PfHsp70-1.

The Role of Non-Canonical Hsp70s (Hsp110/Grp170) in Cancer.

Although cancers account for over 16% of all global deaths annually, at present, no reliable therapies exist for most types of the disease. As protein folding facilitators, heat shock proteins (Hsps) play an important role in cancer development. Not surprisingly, Hsps are among leading anticancer drug targets. Generally, Hsp70s are divided into two main subtypes: canonical Hsp70 (Escherichia coli Hsp70/DnaK homologues) and the non-canonical (Hsp110 and Grp170) members. These two main Hsp70 groups are delineated from each other by distinct structural and functional specifications. Non-canonical Hsp70s are considered as holdase chaperones, while canonical Hsp70s are refoldases. This unique characteristic feature is mirrored by the distinct structural features of these two groups of chaperones. Hsp110/Grp170 members are larger as they possess an extended acidic insertion in their substrate binding domains. While the role of canonical Hsp70s in cancer has received a fair share of attention, the roles of non-canonical Hsp70s in cancer development has received less attention in comparison. In the current review, we discuss the structure-function features of non-canonical Hsp70s members and how these features impact their role in cancer development. We further mapped out their interactome and discussed the prospects of targeting these proteins in cancer therapy.

Genetics of Peripartum Cardiomyopathy: Current Knowledge, Future Directions and Clinical Implications.

Peripartum cardiomyopathy (PPCM) is a condition in which heart failure and systolic dysfunction occur late in pregnancy or within months following delivery. Over the last decade, genetic advances in heritable cardiomyopathy have provided new insights into the role of genetics in PPCM. In this review, we summarise current knowledge of the genetics of PPCM and potential avenues for further research, including the role of molecular chaperone mutations in PPCM. Evidence supporting a genetic basis for PPCM has emanated from observations of familial disease, overlap with familial dilated cardiomyopathy, and sequencing studies of PPCM cohorts. Approximately 20% of PPCM patients screened for cardiomyopathy genes have an identified pathogenic mutation, with TTN truncations most commonly implicated. As a stress-associated condition, PPCM may be modulated by molecular chaperones such as heat shock proteins (Hsps). Recent studies have led to the identification of Hsp mutations in a PPCM model, suggesting that variation in these stress-response genes may contribute to PPCM pathogenesis. Although some Hsp genes have been implicated in dilated cardiomyopathy, their roles in PPCM remain to be determined. Additional areas of future investigation may include the delineation of genotype-phenotype correlations and the screening of newly-identified cardiomyopathy genes for their roles in PPCM. Nevertheless, these findings suggest that the construction of a family history may be advised in the management of PPCM and that genetic testing should be considered. A better understanding of the genetics of PPCM holds the potential to improve treatment, prognosis, and family management.

Interplay of COVID-19 and cardiovascular diseases in Africa: an observational snapshot.

The COVID-19 pandemic, which started around December 2019 has, at present, resulted in over 450,000 deaths globally, and approximately 1% of these deaths have been reported in Africa. Despite the high prevalence of COVID-19 risk factors, namely: hypertension, diabetes, chronic pulmonary disease, cardiovascular diseases (CVDs) such as rheumatic heart disease, compromised immunity and obesity, low case fatality rates have been recorded in many parts of Africa so far. COVID-19 severity has previously been shown to be worse in patients with CVD and hypertension. We observed the severity of COVID-19 and mortality rates in Africa, and compared outcomes with prevalence of established risk factors (hypertension and CVD). We stratified data as per the United Nations' 5 African subregions. North African countries show a positive association between the risk factors and the mortality rates from COVID-19. However, we observed discordant patterns in the relationship between COVID-19, and either CVD or hypertension, in sub-Saharan African countries. In this paper, we also review the pathogenesis of SARS-CoV-2 infection and how it worsens CVD and postulate that the differences in modulation of the renin-angiotensin-aldosterone system (RAAS) axis which controls angiotensin-converting enzyme (ACE)/ACE2 balance may be an important determinant of COVID-19 outcomes in Africa.

Plasmodium falciparum R2TP complex: driver of parasite Hsp90 function.

Heat shock protein 90 (Hsp90) is essential for the development of the main malaria agent, Plasmodium falciparum. Inhibitors that target Hsp90 function are known to not only kill the parasite, but also reverse resistance of the parasite to traditional antimalarials such as chloroquine. For this reason, Hsp90 has been tagged as a promising antimalarial drug target. As a molecular chaperone, Hsp90 facilitates folding of proteins such as steroid hormone receptors and kinases implicated in cell cycle and development. Central to Hsp90 function is its regulation by several co-chaperones. Various co-chaperones interact with Hsp90 to modulate its co-operation with other molecular chaperones such as Hsp70 and to regulate its interaction with substrates. The role of Hsp90 in the development of malaria parasites continues to receive research attention, and several Hsp90 co-chaperones have been mapped out. Recently, focus has shifted to P. falciparum R2TP proteins, which are thought to couple Hsp90 to a diverse set of client proteins. R2TP proteins are generally known to form a complex with Hsp90, and this complex drives multiple cellular processes central to signal transduction and cell division. Given the central role that the R2TP complex may play, the current review highlights the structure-function features of Hsp90 relative to R2TPs of P. falciparum.

The Link That Binds: The Linker of Hsp70 as a Helm of the Protein's Function.

The heat shock 70 (Hsp70) family of molecular chaperones plays a central role in maintaining cellular proteostasis. Structurally, Hsp70s are composed of an N-terminal nucleotide binding domain (NBD) which exhibits ATPase activity, and a C-terminal substrate binding domain (SBD). The binding of ATP at the NBD and its subsequent hydrolysis influences the substrate binding affinity of the SBD through allostery. Similarly, peptide binding at the C-terminal SBD stimulates ATP hydrolysis by the N-terminal NBD. Interdomain communication between the NBD and SBD is facilitated by a conserved linker segment. Hsp70s form two main subgroups. Canonical Hsp70 members generally suppress protein aggregation and are also capable of refolding misfolded proteins. Hsp110 members are characterized by an extended lid segment and their function tends to be largely restricted to suppression of protein aggregation. In addition, the latter serve as nucleotide exchange factors (NEFs) of canonical Hsp70s. The linker of the Hsp110 family is less conserved compared to that of the canonical Hsp70 group. In addition, the linker plays a crucial role in defining the functional features of these two groups of Hsp70. Generally, the linker of Hsp70 is quite small and varies in size from seven to thirteen residues. Due to its small size, any sequence variation that Hsp70 exhibits in this motif has a major and unique influence on the function of the protein. Based on sequence data, we observed that canonical Hsp70s possess a linker that is distinct from similar segments present in Hsp110 proteins. In addition, Hsp110 linker motifs from various genera are distinct suggesting that their unique features regulate the flexibility with which the NBD and SBD of these proteins communicate via allostery. The Hsp70 linker modulates various structure-function features of Hsp70 such as its global conformation, affinity for peptide substrate and interaction with co-chaperones. The current review discusses how the unique features of the Hsp70 linker accounts for the functional specialization of this group of molecular chaperones.

Comparative structure-function features of Hsp70s of Plasmodium falciparum and human origins.

The heat shock protein 70 (Hsp70) family of molecular chaperones are crucial for the survival and pathogenicity of the main agent of malaria, Plasmodium falciparum. Hsp70 is central to cellular proteostasis and some of its isoforms are essential for survival of the malaria parasite. In addition, they are also implicated in the development of antimalarial drug resistance. For these reasons, they are thought to be potential drug targets, especially in antimalarial combination therapies. However, their high sequence conservation across species presents a hurdle with respect to their selective targeting. The human genome encodes 17 Hsp70 isoforms while P. falciparum encodes for only 6. The structural architecture of Hsp70s is typically characterized by a highly conserved N-terminal nucleotide-binding domain (NBD) and a less conserved C-terminal substrate-binding domain (SBD). The two domains are connected by a highly conserved linker. In spite of their fairly high sequence conservation, Hsp70s from various species possess unique signature motifs that appear to uniquely influence their function. In addition, their cooperation with co-chaperones further regulates their functional specificity. In the current review, bioinformatics tools were used to identify conserved and unique signature motifs in Hsp70s of P. falciparum versus their human counterparts. We discuss the common and distinctive structure-function features of these proteins. This information is important towards elucidating the prospects of selective targeting of parasite heat shock proteins as part of antimalarial design efforts.