The regulation of the thermal stability and affinity of the HSPA5 (Grp78/BiP) by clients and nucleotides is modulated by domains coupling.

The HSPA5 protein (BiP/Grp78) serves as a pivotal chaperone in maintaining cellular protein quality control. As a member of the human HSP70 family, HSPA5 comprises two distinct domains: a nucleotide-binding domain (NBD) and a peptide-binding domain (PBD). In this study, we investigated the interdomain interactions of HSPA5, aiming to elucidate how these domains regulate its function as a chaperone. Our findings revealed that HSPA5-FL, HSPA5-T, and HSPA5-N exhibit varying affinities for ATP and ADP, with a noticeable dependency on Mg2+ for optimal interactions. Interestingly, in ADP assays, the presence of the metal ion seems to enhance NBD binding only for HSPA5-FL and HSPA5-T. Moreover, while the truncation of the C-terminus does not significantly impact the thermal stability of HSPA5, experiments involving MgATP underscore its essential role in mediating interactions and nucleotide hydrolysis. Thermal stability assays further suggested that the NBD-PBD interface enhances the stability of the NBD, more pronounced for HSPA5 than for the orthologous HSPA1A, and prevents self-aggregation through interdomain coupling. Enzymatic analyses indicated that the presence of PBD enhances NBD ATPase activity and augments its nucleotide affinity. Notably, the intrinsic chaperone activity of the PBD is dependent on the presence of the NBD, potentially due to the propensity of the PBD for self-oligomerization. Collectively, our data highlight the pivotal role of allosteric mechanisms in modulating thermal stability, nucleotide interaction, and ATPase activity of HSPA5, underscoring its significance in protein quality control within cellular environments.

Human HSP70-escort protein 1 (hHep1) interacts with negatively charged lipid bilayers and cell membranes.

Human Hsp70-escort protein 1 (hHep1) is a cochaperone that assists in the function and stability of mitochondrial HSPA9. Similar to HSPA9, hHep1 is located outside the mitochondria and can interact with liposomes. In this study, we further investigated the structural and thermodynamic behavior of interactions between hHep1 and negatively charged liposomes, as well as interactions with cellular membranes. Our results showed that hHep1 interacts peripherally with liposomes formed by phosphatidylserine and cardiolipin and remains partially structured, exhibiting similar affinities for both. In addition, after being added to the cell membrane, recombinant hHep1 was incorporated by cells in a dose-dependent manner. Interestingly, the association of HSPA9 with hHep1 improved the incorporation of these proteins into the lipid bilayer. These results demonstrated that hHep1 can interact with lipids also present in the plasma membrane, indicating roles for this cochaperone outside of mitochondria.

Human heat shock cognate protein (HSC70/HSPA8) interacts with negatively charged phospholipids by a different mechanism than other HSP70s and brings HSP90 into membranes.

Heat shock proteins (HSP) are critical elements for the preservation of cellular homeostasis by participating in an array of biological processes. In addition, HSP play an important role in cellular protection from various environmental stresses. HSP are part of a large family of different molecular mass polypeptides, displaying various expression patterns, subcellular localizations, and diversity functions. An unexpected observation was the detection of HSP on the cell surface. Subsequent studies have demonstrated that HSP have the ability to interact and penetrate lipid bilayers by a process initiated by the recognition of phospholipid heads, followed by conformational changes, membrane insertion, and oligomerization. In the present study, we described the interaction of HSPA8 (HSC70), the constitutive cytosolic member of the HSP70 family, with lipid membranes. HSPA8 showed high selectivity for negatively charged phospholipids, such as phosphatidylserine and cardiolipin, and low affinity for phosphatidylcholine. Membrane insertion was mediated by a spontaneous process driven by increases in entropy and diminished by the presence of ADP or ATP. Finally, HSPA8 was capable of driving into the lipid bilayer HSP90 that does not display any lipid biding capacity by itself. This observation suggests that HSPA8 may act as a membrane chaperone.

Thermal aggregates of human mortalin and Hsp70-1A behave as supramolecular assemblies.

The Hsp70 family of heat shock proteins plays a critical function in maintaining cellular homeostasis within various subcellular compartments. The human mitochondrial Hsp70 (HSPA9) has been associated with cellular death, senescence, cancer and neurodegenerative diseases, which is the rational for the name mortalin. It is well documented that mortalin, such as other Hsp70s, is prone to self-aggregation, which is related to mitochondria biogenesis failure. Here, we investigated the assembly, structure and function of thermic aggregates/oligomers of recombinant human mortalin and Hsp70-1A (HSPA1A). Summarily, both Hsp70 thermic aggregates have characteristics of supramolecular assemblies. They display characteristic organized structures and partial ATPase activity, despite their nanometric size. Indeed, we observed that the interaction of these aggregates/oligomers with liposomes is similar to monomeric Hsp70s and, finally, they were non-toxic over neuroblastoma cells. These findings revealed that high molecular mass oligomers of mortalin and Hsp70-1A preserved some of the fundamental functions of these proteins.

Structural studies of the Hsp70/Hsp90 organizing protein of Plasmodium falciparum and its modulation of Hsp70 and Hsp90 ATPase activities.

HOP is a cochaperone belonging to the foldosome, a system formed by the cytoplasmic Hsp70 and Hsp90 chaperones. HOP acts as an adapter protein capable of transferring client proteins from the first to the second molecular chaperone. HOP is a modular protein that regulates the ATPase activity of Hsp70 and Hsp90 to perform its function. To obtain more detailed information on the structure and function of this protein, we produced the recombinant HOP of Plasmodium falciparum (PfHOP). The protein was obtained in a folded form, with a high content of α-helix secondary structure. Unfolding experiments showed that PfHOP unfolds through two transitions, suggesting the presence of at least two domains with different stabilities. In addition, PfHOP primarily behaved as an elongated dimer in equilibrium with the monomer. Small-angle X-ray scattering data corroborated this interpretation and led to the reconstruction of a PfHOP ab initio model as a dimer. Finally, the PfHOP protein was able to inhibit and to stimulate the ATPase activity of the recombinant Hsp90 and Hsp70-1, respectively, of P. falciparum. Our results deepened the knowledge of the structure and function of PfHOP and further clarified its participation in the P. falciparum foldosome.

The application of the vermicomposting process in the bioremediation of diesel contaminated soils.

Polycyclic Aromatic Hydrocarbons (PAHs) are among the environmental pollutants that have very high carcinogenic and mutagenic activity. Among hundreds of different PAHs, 17 are considered priority pollutants and routinely monitored for regulatory purposes. Extended periods of exposure and expensive clean-up costs are typically associated with the vast majority of processes used for the remediation of areas contaminated with PAHs. The results of this study indicate that bioremediation via vermicomposting could be an effective method for remedying soils contaminated with toxic organic compounds, such as PAHs. This study was conducted over 90 days in the presence of various quantities of organic matter (cattle manure) to recover soils contaminated with PAHs. High-performance liquid chromatography (HPLC) was applied to identify PAHs. An evaluation of the toxicity of the final material and the transformation of the organic matter throughout the process was also conducted. The data presented here suggest a relationship between the molar mass of the PAHs and the ability of the vermicomposting process to promote biodegradation. These results suggest that vermicomposting has great potential to be utilized as a tool for the bioremediation of soils impacted by PAHs.

Macrophage reprogramming by negatively charged membrane phospholipids controls infection.

Extracellular vesicles (ECVs) are heterogeneous membrane-enclosed structures containing proteins, nucleic acids, and lipids that participate in intercellular communication by transferring their contents to recipient cells. Although most of the attention has been directed at the biologic effect of proteins and microRNA, the contribution of phospholipids present in ECVs on cellular activation has not been extensively addressed. We investigated the biologic effect of phosphatidylserine (PS) and phosphatidylcholine (PC), 2 phospholipids highly abundant in ECVs. A transcriptomic analysis revealed that ∼4700 genes were specifically modified by exposing peritoneal macrophages to PS or PC liposomes in vivo. Among them, the expression of several chemokines and cytokines was highly upregulated by PS liposome treatment, translating into a massive neutrophil infiltration of the peritoneum capable of neutralizing a septic polymicrobial insult. Both the l and d stereoisomers of PS induced the same response, suggesting that the effect was related to the negative charge of the phospholipid head. We concluded that an increase in the internal negative charge of the cell triggers a signaling cascade activating an innate immune response capable of controlling infection.-Cauvi, D. M., Hawisher, D., Dores-Silva, P. R., Lizardo, R. E., De Maio, A. Macrophage reprogramming by negatively charged membrane phospholipids controls infection.

Structural and functional studies of the Leishmania braziliensis SGT co-chaperone indicate that it shares structural features with HIP and can interact with both Hsp90 and Hsp70 with similar affinities.

Molecular chaperones and co-chaperones play an essential role in the life cycles of protozoa belonging to the genus Leishmania. The small glutamine-rich TPR-containing protein (SGT) is a co-chaperone that can be divided into three domains: N-terminal, tetratricopeptide (TPR) and C-terminal. The TPR domain is responsible for interactions with both Hsp70 and Hsp90; however, the mechanism of interaction and the functionality of SGT are unclear. In this context, we present the structural and functional characterization of Leishmania braziliensis SGT (LbSGT), aiming to elucidate how this co-chaperone interacts with the Hsp90/Hsp70 chaperone machinery. Structurally, the recombinant LbSGT behaves as an α-helical, multidomain and elongated dimer in solution. Despite their low amino acid sequence identity and similarity, LbSGT shares structural properties and domain organization with the Hsp70-interacting protein (HIP) co-chaperone. Functionally, LbSGT is a cognate protein in L. braziliensis promastigote cells and interacts indiscriminately, with similar affinities, with both Hsp90 and Hsp70 chaperones, capable of working as an adaptor protein. Sequence analysis indicates that LbSGT interacts via a dicarboxylate clamp, the same mechanism used by the Hsp90-Hsp70-organizing protein (HOP) co-chaperone. These results suggest that SGT can develop the same function as HOP but using the HIP structural scaffold.

Humification process in different kinds of organic residue by composting and vermicomposting: have microbioreactors really accelerated the process?

The organic matter existing in nature presents as a complex system of various substances. The humic fraction refers to the humic substances (HS) and consists of humic acids (HA), fulvic acids (FA), and humins, according to solubility in aqueous solution. The physical and chemical characteristics of HA, FA, and humins depend on many factors, among which is the type of original organic material. Two processes for the stabilization of organic materials are known worldwide: composting and vermicomposting. Cattle manure, rice straw, sugarcane bagasse, and vegetable wastes from leaves were the organic residues chosen for the composting and vermicomposting processes. In this study, the differences between the HS extracted from such composted and vermicomposted residues were evaluated. The so-extracted HS were evaluated by spectroscopy in the regions of infrared and ultraviolet-visible, and pyrolysis coupled with gas chromatography with mass spectrometric detection is applied. Thus, we expect that the results obtained here indicate which of the two processes is more efficient in the biotransformation of organic residues in a short period with respect to the HS content. It was also observed that the basic units of the humic fractions generated (although they presented different degrees of maturation) are the same. Altogether, the data reported here bring to light that the structures of the HS are very similar, differing in quantities. These results can still be extrapolated to several other raw materials, since the most variable organic matrices were used here to allow this data extrapolation. In addition, the process seems to lead to the formation of more aliphatic substances, counterpoising what is found in the literature.

Soils impacted by PAHs: Would the stabilized organic matter be a green tool for the immobilization of these noxious compounds?

The objective of this study was to investigate the role of stabilized organic matter (vermicompost) and tropical soils in the sorption of naphthalene, anthracene and benzo[a]pyrene. The results obtained for the three compounds were extrapolated for the priority polycyclic aromatic hydrocarbons (PAHs) pollutants according to Environmental Protection Agency (US EPA). To evaluate the sorption process, high performance liquid chromatography was employed and the data was fitted by Freundlich isotherms. The results suggest that the sorption effect generally increases with the number of benzene rings of the PAHs, and that the persistence of PAHs in the environment is possibly related to the number of benzene rings in the PAH molecule. In addition, the pH of the vermicompost can strongly affect the adsorption process in this matrix.

Insights on the structural dynamics of Leishmania braziliensis Hsp90 molecular chaperone by small angle X-ray scattering.

Heat shock protein of 90kDa (Hsp90) is an essential molecular chaperone involved in a plethora of cellular activities which modulate protein homeostasis. During the Hsp90 mechanochemical cycle, it undergoes large conformational changes, oscillating between open and closed states. Although structural and conformational equilibria of prokaryotic and some eukaryotic Hsp90s are known, some protozoa Hsp90 structures and dynamics are poorly understood. In this study, we report the solution structure and conformational dynamics of Leishmania braziliensis Hsp90 (LbHsp90) investigated by small angle X-ray scattering (SAXS). The results indicate that LbHsp90 coexists in open and closed conformations in solution and that the linkers between domains are not randomly distributed. These findings noted interesting features of the LbHsp90 system, opening doors for further conformational studies of other protozoa chaperones.

Structural and functional studies of the Leishmania braziliensis mitochondrial Hsp70: Similarities and dissimilarities to human orthologues.

Heat shock protein 70 kDa (Hsp70) is a conserved molecular chaperone family involved in several functions related to protein homeostasis. In eukaryotes, Hsp70 homologues are found in all cell compartments. The mitochondrial Hsp70 isoform (mtHsp70) is involved in import of mitochondrial matrix proteins as well as their folding and maturation. Moreover, mtHsp70 has the propensity to self-aggregate, and it depends on the action of the co-chaperone Hsp70-escort protein 1 (Hep1) to be produced functional. Here, we analyze the solution structure and function of mtHsp70 of Leishmania braziliensis (LbmtHsp70). This recombinant protein was obtained folded, in the monomeric state and it has an elongated shape. We observed that LbmtHsp70 suffers thermal aggregation that depends on the protein concentration and is composed of domains with different thermal stabilities. LbmtHsp70 interacted with adenosine nucleotides with a thermodynamic signature different from those reported for human orthologues and interacted, driven by both enthalpy and entropy, with L. braziliensis Hep1 (LbHep1) with a nanomolar dissociation constant. Moreover, LbHep1 stimulated the LbmtHsp70 ATPase activity. Since little is known about mitochondrial Hsp70, particularly in protozoa, we believe that our data are of interest for understanding protozoan Hsp70 machinery.

Limited proteolysis of myoglobin opens channel in ferrochelatase-globin complex for iron to zinc transmetallation.

Recombinant ferrochelatase (BsFECH) from Bacillus subtilis expressed in Escherichia coli BL21(DE3) was found by UV-visible spectroscopy to bind the model substrate tetraphenylporphyrin-sulfonate, TPPS, with Ka=3.8 10(5)mol/L in aqueous phosphate buffer pH 5.7 at 30°C, and to interact with metmyoglobin with Ka=1.07±0.13 10(5)mol/L at 30°C. The iron/zinc exchange in myoglobin occurring during maturation of Parma hams seems to depend on such substrate binding to BsFECH and was facilitated by limited pepsin proteolysis of myoglobin to open a reaction channel for metal exchange still with BsFECH associated to globin. BsFECH increased rate of zinc insertion in TPPS significantly and showed saturation kinetics with an apparent binding constant of Zn(II) to the [enzyme-TPPS] complex of 1.3 10(4)mol/L and a first-order rate constant of 6.6 10(-1)s(-1) for dissociation of the tertiary complex, a similar pattern was found for zinc/iron transmetallation in myoglobin.

A review of multi-domain and flexible molecular chaperones studies by small-angle X-ray scattering.

Intrinsic flexibility is closely related to protein function, and a plethora of important regulatory proteins have been found to be flexible, multi-domain or even intrinsically disordered. On the one hand, understanding such systems depends on how these proteins behave in solution. On the other, small-angle X-ray scattering (SAXS) is a technique that fulfills the requirements to study protein structure and dynamics relatively quickly with few experimental limitations. Molecular chaperones from Hsp70 and Hsp90 families are multi-domain proteins containing flexible and/or disordered regions that play central roles in cellular proteostasis. Here, we review the structure and function of these proteins by SAXS. Our general approach includes the use of SAXS data to determine size and shape parameters, as well as protein shape reconstruction and their validation by using accessory biophysical tools. Some remarkable examples are presented that exemplify the potential of the SAXS technique. Protein structure can be determined in solution even at limiting protein concentrations (for example, human mortalin, a mitochondrial Hsp70 chaperone). The protein organization, flexibility and function (for example, the J-protein co-chaperones), oligomeric status, domain organization, and flexibility (for the Hsp90 chaperone and the Hip and Hep1 co-chaperones) may also be determined. Lastly, the shape, structural conservation, and protein dynamics (for the Hsp90 chaperone and both p23 and Aha1 co-chaperones) may be studied by SAXS. We believe this review will enhance the application of the SAXS technique to the study of the molecular chaperones.

Human mitochondrial Hsp70 (mortalin): shedding light on ATPase activity, interaction with adenosine nucleotides, solution structure and domain organization.

The human mitochondrial Hsp70, also called mortalin, is of considerable importance for mitochondria biogenesis and the correct functioning of the cell machinery. In the mitochondrial matrix, mortalin acts in the importing and folding process of nucleus-encoded proteins. The in vivo deregulation of mortalin expression and/or function has been correlated with age-related diseases and certain cancers due to its interaction with the p53 protein. In spite of its critical biological roles, structural and functional studies on mortalin are limited by its insoluble recombinant production. This study provides the first report of the production of folded and soluble recombinant mortalin when co-expressed with the human Hsp70-escort protein 1, but it is still likely prone to self-association. The monomeric fraction of mortalin presented a slightly elongated shape and basal ATPase activity that is higher than that of its cytoplasmic counterpart Hsp70-1A, suggesting that it was obtained in the functional state. Through small angle X-ray scattering, we assessed the low-resolution structural model of monomeric mortalin that is characterized by an elongated shape. This model adequately accommodated high resolution structures of Hsp70 domains indicating its quality. We also observed that mortalin interacts with adenosine nucleotides with high affinity. Thermally induced unfolding experiments indicated that mortalin is formed by at least two domains and that the transition is sensitive to the presence of adenosine nucleotides and that this process is dependent on the presence of Mg2+ ions. Interestingly, the thermal-induced unfolding assays of mortalin suggested the presence of an aggregation/association event, which was not observed for human Hsp70-1A, and this finding may explain its natural tendency for in vivo aggregation. Our study may contribute to the structural understanding of mortalin as well as to contribute for its recombinant production for antitumor compound screenings.