The C‐terminal extension of Mycobacterium tuberculosis Hsp16.3 regulates its oligomerization, subunit exchange dynamics and chaperone function

Lysine acetylation of Hsp16.3: Effect on its structure, chaperone function and influence towards the growth of Mycobacterium tuberculosis

Hsp16.3 plays a vital role in the slow growth of Mycobacterium tuberculosis via its chaperone function. Many secretory proteins, including Hsp16.3 undergo acetylation in vivo. Seven lysine (K) residues (K64, K78, K85, K114, K119, K132 and K136) in Hsp16.3 are acetylated inside pathogen. However, how lysine acetylation affects its structure, chaperone function and pathogen's growth is still elusive. We examined these aspects by executing in vitro chemical acetylation (acetic anhydride modification) and by utilizing a lysine acetylation mimic mutant (Hsp16.3-K64Q/K78Q/K85Q/K114Q/K119Q/K132Q/K136Q). Far- and near-UV CD measurements revealed that the chemically acetylated proteins(s) and acetylation mimic mutant has altered secondary and tertiary structure than unacetylated/wild-type protein. The chemical modification and acetylation mimic mutation also disrupted the oligomeric assembly, increased surface hydrophobicity and reduced stability of Hsp16.3, as revealed by GF-HPLC, 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid binding and urea denaturation experiments, respectively. These structural changes collectively led to an enhancement in chaperone function (aggregation and thermal inactivation prevention ability) of Hsp16.3. Moreover, when the H37Rv strain expressed the acetylation mimic mutant protein, its growth was slower in comparison to the strain expressing the wild-type/unacetylated Hsp16.3. Altogether, these findings indicated that lysine acetylation improves the chaperone function of Hsp16.3 which may influence pathogen's growth in host environment.

Probing the interaction and aggregation of lysozyme in presence of organophosphate pesticides: a comprehensive spectroscopic, calorimetric, and in-silico investigation

Organophosphorus pesticides (OPs) are widely used in agriculture and may contaminate food or water, leading to potential health risks. However, there are few reports on the effect of OPs on protein conformation and aggregation. Hence, in this paper, we have characterized the impact of two OPs, chlorpyrifos (CPF) and methyl parathion (Para), on the model protein HEWL using biophysical and computational methods. The steady-state and time-resolved spectroscopy, Circular dichroism (CD), molecular dynamics simulation, and isothermal titration calorimetry were employed to investigate the binding interactions between HEWL and OPs. The steady-state and time-resolved fluorescence spectroscopy confirm the presence of both static and dynamic quenching between OPs and proteins. Based on fluorescence, MD, and CD results, it was found that the OPs not only show strong binding but also destabilize the protein structure and alter the secondary and tertiary structure of the protein. The molecular docking results showed that OPs entered the binding pocket of the HEWL molecule and interacted through hydrophobic and hydrogen bond interactions. The thermodynamic studies indicated that the binding was spontaneous and OPs have shown an effect on the aggregation process of HEWL. Finally, the protein aggregation process was studied using fluorescence and SDS-PAGE studies in the presence of both the OPs and found to enhance the aggregation process in the presence of OPs. These results provide insights into the potential health risks associated with OPs and highlight the importance of understanding their interactions with biological macromolecules.Communicated by Ramaswamy H. Sarma.

Impact of nanoparticles on amyloid β-induced Alzheimer's disease, tuberculosis, leprosy and cancer: a systematic review

Nanotechnology is an interdisciplinary domain of science, technology and engineering that deals with nano-sized materials/particles. Usually, the size of nanoparticles lies between 1 and 100 nm. Due to their small size and large surface area-to-volume ratio, nanoparticles exhibit high reactivity, greater stability and adsorption capacity. These important physicochemical properties attract scientific community to utilize them in biomedical field. Various types of nanoparticles (inorganic and organic) have broad applications in medical field ranging from imaging to gene therapy. These are also effective drug carriers. In recent times, nanoparticles are utilized to circumvent different treatment limitations. For example, the ability of nanoparticles to cross the blood-brain barrier and having a certain degree of specificity towards amyloid deposits makes themselves important candidates for the treatment of Alzheimer's disease. Furthermore, nanotechnology has been used extensively to overcome several pertinent issues like drug-resistance phenomenon, side effects of conventional drugs and targeted drug delivery issue in leprosy, tuberculosis and cancer. Thus, in this review, the application of different nanoparticles for the treatment of these four important diseases (Alzheimer's disease, tuberculosis, leprosy and cancer) as well as for the effective delivery of drugs used in these diseases has been presented systematically. Although nanoformulations have many advantages over traditional therapeutics for treating these diseases, nanotoxicity is a major concern that has been discussed subsequently. Lastly, we have presented the promising future prospective of nanoparticles as alternative therapeutics. In that section, we have discussed about the futuristic approach(es) that could provide promising candidate(s) for the treatment of these four diseases.

Role of ATP-Small Heat Shock Protein Interaction in Human Diseases

Adenosine triphosphate (ATP) is an important fuel of life for humans and Mycobacterium species. Its potential role in modulating cellular functions and implications in systemic, pulmonary, and ocular diseases is well studied. Plasma ATP has been used as a diagnostic and prognostic biomarker owing to its close association with disease’s progression. Several stresses induce altered ATP generation, causing disorders and illnesses. Small heat shock proteins (sHSPs) are dynamic oligomers that are dominantly β-sheet in nature. Some important functions that they exhibit include preventing protein aggregation, enabling protein refolding, conferring thermotolerance to cells, and exhibiting anti-apoptotic functions. Expression and functions of sHSPs in humans are closely associated with several diseases like cataracts, cardiovascular diseases, renal diseases, cancer, etc. Additionally, there are some mycobacterial sHSPs like Mycobacterium leprae HSP18 and Mycobacterium tuberculosis HSP16.3, whose molecular chaperone functions are implicated in the growth and survival of pathogens in host species. As both ATP and sHSPs, remain closely associated with several human diseases and survival of bacterial pathogens in the host, therefore substantial research has been conducted to elucidate ATP-sHSP interaction. In this mini review, the impact of ATP on the structure and function of human and mycobacterial sHSPs is discussed. Additionally, how such interactions can influence the onset of several human diseases is also discussed.

Interaction of constituents of MDT regimen for leprosy with Mycobacterium leprae HSP18: impact on its structure and function

Mycobacterium leprae, the causative organism of leprosy, harbors many antigenic proteins, and one such protein is the 18-kDa antigen. This protein belongs to the small heat shock protein family and is commonly known as HSP18. Its chaperone function plays an important role in the growth and survival of M. leprae inside infected hosts. HSP18/18-kDa antigen is often used as a diagnostic marker for determining the efficacy of multidrug therapy (MDT) in leprosy. However, whether MDT drugs (dapsone, clofazimine, and rifampicin) do interact with HSP18 and how these interactions affect its structure and chaperone function is still unclear. Here, we report evidence of HSP18-dapsone/clofazimine/rifampicin interaction and its impact on the structure and chaperone function of HSP18. These three drugs interact efficiently with HSP18 (having submicromolar binding affinity) with 1 : 1 stoichiometry. Binding of these MDT drugs to the 'α-crystallin domain' of HSP18 alters its secondary structure and tryptophan micro-environment. Furthermore, surface hydrophobicity, oligomeric size, and thermostability of the protein are reduced upon interaction with these three drugs. Eventually, all these structural alterations synergistically decrease the chaperone function of HSP18. Interestingly, the effect of rifampicin on the structure, stability, and chaperone function of this mycobacterial small heat shock protein is more pronounced than the other two MDT drugs. This reduction in the chaperone function of HSP18 may additionally abate M. leprae survivability during multidrug treatment. Altogether, this study provides a possible foundation for rational designing and development of suitable HSP18 inhibitors in the context of effective treatment of leprosy.

Mycobacterium tuberculosis Heat-Shock Protein 16.3 Induces Macrophage M2 Polarization Through CCRL2/CX3CR1

Mycobacterium tuberculosis, the pathogen of tuberculosis (TB), can survive in host macrophages and induce macrophages to M2 phenotype might result in latent MTB infection. During the latent phase, the expression of MTB heat-shock protein 16.3 (Hsp16.3) is markedly increased among most of bacterial proteins, but the role of Hsp16.3 in macrophage M2 polarization is not clear. In this work, we found that macrophages incubated with 100 ng/ml MTB Hsp16.3 increased the production of Arg-1, IL-10, TGF-beta, and CD206. These results showed that MTB Hsp16.3 may induce macrophage M2 phenotype. And the interaction of Hsp16.3 with macrophages was found to depend on chemokine receptors CCRL2 and CX3CR1. Additionally, we used overexpression and silencing techniques to further verify the effect of CCRL2 and CX3CR1 on MTB Hsp16.3-induced M2 polarization macrophages. Furthermore, we explored the downstream signaling molecules of CCRL2 and CX3CR1 and we found MTB Hsp16.3 altered the signal transduction of the AKT/ERK/p38-MAPK. Taken together, this study provides evidence that MTB Hsp16.3 promotes macrophages to M2 phenotype and explores its underlying mechanism.

Role of Molecular Interactions and Oligomerization in Chaperone Activity of Recombinant Acr from Mycobacterium tuberculosis

Background:

The chaperone activity of Mycobacterium tuberculosis Acr is an important function that helps to prevent misfolding of protein substrates inside the host, especially in conditions of hypoxia.

Objectives:

The aim of this study was to establish the correlation of structure and function of recombinant Acr proteins both before and after gel filtration chromatography. The aim was also to find the oligomeric conformation of these samples and use this information to explain differences in activit.

Material and Methods:

M. tuberculosis acr gene was cloned with an N-terminal His-tag in pET28a and expressed with IPTG induction in BL2 (DE3) competent Escherichia coli. The activity of a recombinant Acr without gel filtration was checked by preventing thermal aggregation of citrate synthase at 45°C and the chaperone activity against insulin B chain aggregation at 60°C and 37°C. On further purification using gel filtration chromatography, the protein was again tested for chaperone activity using insulin as substrate at 37°C with two types of samples without and with gel filtration designated A and B respectively. The effects of pre–heat treatment at 60 °C on chaperone activity of both A and B samples were studied by performing the chaperone assay at 37°C.

Results:

The level of expression was 40 to 50 mg /l. The protein was expressed in a soluble form at 37°C and subsequently purified by a 3 step gradient of imidazole using Ni-NTA resin. Gel filtration chromatography showed recombinant Acr to be a mixture of 9 to 15-mers, whereas Native-PAGE analysis showed a large proportion of 5 and 7 mers in the non gel-filtered sample, while non gel –filtered samples showed more proportions of higher size oligomers. The chaperone activity of non gel-filtered (A) samples was less than gel-filtered (B) samples at 37°C with 24 µM required of A for complete inhibition as compared to 6 µM of B. The chaperone activity of non gel–filtered samples at 60°C showed complete inhibition of activity at a concentration of 44 µM. Molecular interaction studies showed influence of size of oligomers on molecular coverage of insulin B chain. Pre-heat treatment improved the activity only after the gel filtration.

Conclusions:

The larger proportion of monomers in the non gel-filtered sample could explain the difference in activity as compared to the gel-filtered samples in terms of molecular interaction with insulin. Increased oligomer size favorably affected secondary structure, a finding not reported so far, and warranting further investigation. A molecular level interaction of inhibition was predicted using Avogadro number of molecules and oligomer size. The difference in activity after pre–heat treatment seemed to indicate an important role for oligomerization.

Structure, stability and chaperone function of Mycobacterium leprae Heat Shock Protein 18 are differentially affected upon interaction with gold and silver nanoparticles

Gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) have several biomedical applications. However, the effective usage of these two nanoparticles is impeded due to limited understanding of their interaction with proteins including small heat shock proteins (sHSPs). Specifically, no evidences of interaction of these two nanoparticles with HSP18 (an antigenic protein) which is an important factor for the growth and survival of M. leprae (the causative organism of leprosy) are available in the literature. Here, we report for the first time evidences of "HSP18-AuNPs/AgNPs interaction" and its impact on the structure and chaperone function of HSP18. Interaction of citrate-capped AuNPs/AgNPs (~20 nm diameter) to HSP18 alters the secondary and tertiary structure of HSP18 in a distinctly opposite manner; while "HSP18-AuNPs interaction" leads to oligomeric association, "HSP18-AgNPs interaction" results in oligomeric dissociation of the protein. Surface hydrophobicity, thermal stability, chaperone function of HSP18 and survival of thermally stressed E. coli harbouring HSP18 are enhanced upon AuNPs interaction, while all of them are reduced upon interaction with AgNPs. Altogether, our study reveals that HSP18 is an important drug target in leprosy and its chaperone function may possibly plays a vital role in the growth and survival of M. leprae pathogen in infected hosts.

The impact of different mutations at arginine141 on the structure, subunit exchange dynamics and chaperone activity of Hsp16.3

Hsp16.3, a molecular chaperone, plays a vital role in the growth and survival of Mycobacterium tuberculosis inside the host. We previously reported that deletion of three amino acid residues (¹⁴² STN¹⁴⁴ ) from C-terminal extension (CTE) of Hsp16.3 triggers its structural perturbation and increases its chaperone activity, which reaches its apex upon the deletion of its entire CTE (¹⁴¹ RSTN¹⁴⁴ ). Thus, we hypothesized that Arg141 (R141) and Ser142 (S142) in the CTE of Hsp16.3 possibly hold the key in maintaining its native-like structure and chaperone activity. To test this hypothesis, we generated two deletion mutants in which R141 and S142 were deleted individually (Hsp16.3ΔR141 and Hsp16.3ΔS142) and three substitution mutants in which R141 was replaced by lysine (Hsp16.3R141K), alanine (Hsp16.3R141A), and glutamic acid (Hsp16.3R141E), respectively. Hsp16.3ΔS142 or Hsp16.3R141K mutant has native-like structure and chaperone activity. Deletion of R141 from the CTE (Hsp16.3ΔR141) perturbs the secondary and tertiary structure, lowers the subunit exchange dynamics and decreases the chaperone activity of Hsp16.3. But, the substitution of R141 with alanine (Hsp16.3R141A) or glutamic acid (Hsp16.3R141E) perturbs its secondary and tertiary structure. Surprisingly, such charge tampering of R141 enhances the subunit exchange dynamics and chaperone activity of Hsp16.3. Interestingly, neither the deletion of R141/S142 nor the substitution of R141 with lysine, alanine and glutamic acid affects the oligomeric mass/size of Hsp16.3. Overall, our study suggests that R141 (especially the positive charge on R141) plays a crucial role in maintaining the native-like structure as well as in regulating subunit exchange dynamics and chaperone activity of Hsp16.3.

HspX promotes the polar localization of mycobacterial protein aggregates

Misfolding of translated proteins occurs in all domains of life. In most cells, misfolded proteins coalesce in discrete aggregates at distinct cellular locations. In many bacteria, including mycobacteria, protein aggregates are located at the cellular pole. Yet the mechanism by which aggregates are sorted to the mycobacterial pole is not known. Here, we show that in Mycobacterium smegmatis, the small heat shock protein HspX plays a critical role in the polar localization of aggregates of a model fluorescent misfolded protein, GLR103. HspX itself has a polar localization, which is dependent on its N-terminal domain. In a strain deleted for hspX, GLR103 is less liable to aggregation and no longer localizes to the pole, and redirecting HspX to the septum radically disrupts the normal polar localization of GLR103 aggregates. To further investigate the role of HspX in native protein aggregation, we performed semi-quantitative mass-spectrometry of mycobacterial protein aggregates in wild-type, hspX-deleted and hspX-overexpressing strains. We identified a subset of proteins that appeared to be HspX-dependent for aggregate formation. Furthermore, we demonstrate that for validated native protein aggregates, sorting to the cellular pole following proteotoxic stress required HspX. In summary, we have identified the cellular function of HspX in Mycobacterium smegmatis as both a pro-aggregase and polar sortase.

A New Functional Model for Prediction of Chaperone Activity of the Recombinant M. tb Acr (α-Crystallin) Using Insulin as Substrate

Mycobacterium tuberculosis Acr is an important protein expressed in latent tuberculosis which is active as an oligomer in preventing misfolding of cellular proteins. In this study, Mycobacterium alpha crystallin (acr) gene was cloned and expressed in Escherichia coli (E. coli). The recombinant Acr protein was purified by Nickel-NTA resin. The oligomeric state of Acr was confirmed by gel filtration chromatography using Sephacryl S-200 and Native-PAGE. Studies of chaperone activity were performed with insulin as a substrate at different mole ratios of Acr with 2 types of samples, His tag elutes (H) and His tag elutes with gel filtration (G). It was observed that the ratio of different sizes of oligomers (9 to 24 mers) had a significant effect on chaperone activity. Using the mole ratio of Acr for both (H) and (G) samples to insulin B chain and ratio of oligomers, we determined the number of Acr molecules binding to insulin as a model substrate. We found that if 1.5% of the insulin B chains are covered completely by the (G) samples, aggregation is completely inhibited as compared to 6% with (H) samples. Pre-heat treatment studies were carried out at 37°C, 60°C, and 70°C. Far-ultraviolet Circular Dichroism (UV-CD) analysis provided fresh insights into the role of β-sheets and α-helices in chaperone activity, particularly in (H) samples suggesting a reversible conformational transition from helices to sheets. This enabled us to formulate a functional model for binding of Acr to insulin B chains which incorporated 4 types of secondary structure molecules. This might be a useful tool for analyzing in vitro preparations of recombinant Acr and build more consensuses on the structure-activity relationship especially in terms of oligomeric ratios.

Prediction of recombinant Mycobacterium tuberculosis α-crystallin oligomer chaperone activity using polynomial graphs

Background: Mycobacterial α-crystallin (Acr) is a chaperone that prevents misfolding of proteins when Mycobacterium tuberculosis is found in a latent form in the host tissue. Methods: Using insulin as a model substrate and utilizing polynomial graphs, we attempted to predict molecular-level interactions that are a function of the oligomeric state of the recombinant protein. The chaperone activity of the recombinant oligomeric Acr was measured at 60°C with Acr samples obtained before gel filtration chromatography and compared with a gel-filtered sample. Results: The polynomial graphs constructed showed improved molecular coverage of the insulin B chain by the oligomer. The 2 nd order coefficient is the one that changes with the oligomeric ratio of Acr and improves chaperone activity. Polynomial analysis suggested that it could be a useful parameter to predict chaperone activity for potential in vitro batches of M. tuberculosis Acr based on the dynamic nature of the association and disassociation of oligomers. Conclusions: The results showed that coverage of insulin B chain improved with higher ratio of 9-mer as compared to lower ratios. This was shown by both simulation plots and actual assay data. The polynomial graphs showed increase in the 2 nd order coefficient, thus suggesting the important role of oligomerisation in improved molecular coverage of insulin B chain.

Prediction of recombinant Mycobacterium tuberculosis α-crystallin oligomer chaperone activity using polynomial graphs

Background: Mycobacterial α-crystallin (Acr) is a chaperone that prevents misfolding of proteins when Mycobacterium tuberculosis is found in a latent form in the host tissue. Methods: Using insulin as a model substrate and utilizing polynomial graphs, we attempted to predict molecular-level interactions that are a function of the oligomeric state of the recombinant protein. The chaperone activity of the recombinant oligomeric Acr was measured at 60°C with Acr samples obtained before gel filtration chromatography and compared with a gel-filtered sample. Results: The polynomial graphs constructed showed improved molecular coverage of the insulin B chain by the oligomer. The 2 nd order coefficient is the one that changes with the oligomeric ratio of Acr and improves chaperone activity. Polynomial analysis suggested that it could be a useful parameter to predict chaperone activity for potential in vitro batches of M. tuberculosis Acr based on the dynamic nature of the association and disassociation of oligomers. Conclusions: The results showed that coverage of insulin B chain improved with higher ratio of 9-mer as compared to lower ratios. This was shown by both simulation plots and actual assay data. The polynomial graphs showed increase in the 2 nd order coefficient, thus suggesting the important role of oligomerisation in improved molecular coverage of insulin B chain.

Insights into Macrophage Autophagy in Latent Tuberculosis Infection: Role of Heat Shock Protein 16.3

Tuberculosis (TB) is a major bacterial infectious disease worldwide that is predominantly caused by Mycobacterium tuberculosis (Mtb). The comorbidity of multiple drug-resistant TB strains with HIV and diabetes is widespread. In the presence of these diseases, host immunity is weakened, allowing the recovery of dormant bacilli and leading to recurrent TB infection. As an important component of the host innate and adaptive immune responses, macrophage autophagy plays a significant role in protecting the host against TB. However, dormant bacilli can escape from autophagosomes and/or suppress autophagy, thus surviving within the host for an extended period of time, although the underlying mechanism remains elusive. Heat shock protein 16.3 (Hsp16.3, HspX, Rv2031c, and Acr) is one of the immunodominant proteins expressed during latent TB infection (LTBI). It may help maintain the protein stability and long-term viability of Mtb by inhibiting macrophage autophagy, resulting in LBTI. In this review, we discuss how dormant bacilli escape from autophagosomes, and we focus on the role of Hsp16.3 in regulating macrophage autophagy in LTBI so as to provide a firm basis for further studies. Hsp16.3 may represent a potential biomarker of LTBI and novel pharmacological target for anti-tubercular drugs.