The dimeric structure of the Cpn60.2 chaperonin of Mycobacterium tuberculosis at 2.8 Å reveals possible modes of function

Crystal structures of dimeric and heptameric mtHsp60 reveal the mechanism of chaperonin inactivation

Mitochondrial Hsp60 (mtHsp60) plays a crucial role in maintaining the proper folding of proteins in the mitochondria. mtHsp60 self-assembles into a ring-shaped heptamer, which can further form a double-ring tetradecamer in the presence of ATP and mtHsp10. However, mtHsp60 tends to dissociate in vitro, unlike its prokaryotic homologue, GroEL. The molecular structure of dissociated mtHsp60 and the mechanism behind its dissociation remain unclear. In this study, we demonstrated that Epinephelus coioides mtHsp60 (EcHsp60) can form a dimeric structure with inactive ATPase activity. The crystal structure of this dimer reveals symmetrical subunit interactions and a rearranged equatorial domain. The α4 helix of each subunit extends and interacts with its adjacent subunit, leading to the disruption of the ATP-binding pocket. Furthermore, an RLK motif in the apical domain contributes to stabilizing the dimeric complex. These structural and biochemical findings provide new insights into the conformational transitions and functional regulation of this ancient chaperonin.

Detection of a target protein (GroEl2) in Mycobacterium tuberculosis using a derivative of 1,2,4-triazolethiols

Herein, we identified a potent lead compound RRA2, within a series of 54 derivatives of 1,2,4-triazolethiols (exhibit good potency as an anti-mycobacterial agents) against intracellular Mycobacterium tuberculosis (Mtb). Compound RRA2 showed significant mycobactericidal activity against active stage Mycobacterium bovis BCG and Mtb with minimum inhibitory concentration (MIC) values of 2.3 and 2.0 µg/mL, respectively. At MIC value, RRA2 compound yielded 0.82 log reduction of colony-forming unit (cfu) against non-replicating Mtb. Furthermore, RRA2 compound was selected for further target identification due to the presence of alkyne group, showing higher selectivity index (> 66.66 ± 0.22, in non-replicating stage). Using "click" chemistry, we synthesized the biotin linker-RRA2 conjugate, purified with HPLC method and confirmed the conjugation of biotin linker-RRA2 complex by HR-MS analysis. Furthermore, we successfully pulled down and identified a specific target protein GroEl2, from Mtb whole-cell extract. Furthermore, computational molecular modeling indicated RRA2 could interact with GroEl2, which explains the structure-activity relationship observed in this study. GroEL-2 identified a potent and specific target protein for RRA 2 compound in whole cell extract of Mtb H37Ra.

Interaction mechanism of Mycobacterium tuberculosis GroEL2 protein with macrophage Lectin-like, oxidized low-density lipoprotein receptor-1: An integrated computational and experimental study

BACKGROUND

Bacterial surface proteins act as potential adhesins or invasins. The GroEL is a signal peptide-free surface expressed protein that aids adhesion in Escherichia coli by binding to LOX-1 receptor of the host cells. Mycobacterium tuberculosis (Mtb) expresses GroEL2 protein, having high level sequence identity with E. coli GroEL. This study investigates the interaction mechanism of GroEL2 protein of Mtb with LOX-1 of macrophages using integrated computational and experimental approach.

METHODS

Mtb GroEL2 protein was purified as histidine tagged protein using Ni-NTA chromatography. Confocal and scanning electron microscopies were used to study the uptake of GroEL2 coated fluorescent latex beads through the LOX-1 receptor in RAW264.7 macrophage cell line. Docking studies were performed to understand the interaction between the GroEL2 and LOX-1 proteins. Polyinosinic acid (PIA) was used as a LOX-1 inhibitor in both in silico and in vitro experiments.

RESULTS

GroEL2 protein coating enhances uptake of latex beads into macrophages through LOX-1 receptor. LOX-1 inhibitor PIA decreased the uptake of GroEL2 coated latex beads. GroEL2 interacts with the key ligand binding regions of the LOX-1 receptor, such as the basic spine and the saddle hydrophobic patch. PIA molecule destabilized the LOX-1-GroEL2 docked complex.

CONCLUSION

Surface associated GroEL2 protein of Mtb is a potential ligand for macrophage LOX-1 receptor. Interaction between GroEL2 and LOX-1 receptor may be utilized by Mtb to gain its intracellular access.

GENERAL SIGNIFICANCE

Surface associated GroEL2 of Mtb may bind to the macrophage LOX-1 receptor, enabling the internalization of the bacteria and progression of the infection.

Interplays between copper and Mycobacterium tuberculosis GroEL1

The chaperone GroEL1 enhances copper tolerance during Mycobacterium bovis BCG biofilm formation. The binding of copper ions to the GroEL1 histidine-rich region protects the chaperone from destabilization and increases its ATPase activity.

Reconstitution of Pure Chaperonin Hetero-Oligomer Preparations in Vitro by Temperature Modulation

Chaperonins are large, essential, oligomers that facilitate protein folding in chloroplasts, mitochondria, and eubacteria. Plant chloroplast chaperonins are comprised of multiple homologous subunits that exhibit unique properties. We previously characterized homogeneous, reconstituted, chloroplast-chaperonin oligomers in vitro, each composed of one of three highly homologous beta subunits from A. thaliana. In the current work, we describe alpha-type subunits from the same species and investigate their interaction with β subtypes. Neither alpha subunit was capable of forming higher-order oligomers on its own. When combined with β subunits in the presence of Mg-ATP, only the α2 subunit was able to form stable functional hetero-oligomers, which were capable of refolding denatured protein with native chloroplast co-chaperonins. Since β oligomers were able to oligomerize in the absence of α, we sought conditions under which αβ hetero-oligomers could be produced without contamination of β homo-oligomers. We found that β2 subunits are unable to oligomerize at low temperatures and used this property to obtain homogenous preparations of functional α2β2 hetero-oligomers. The results of this study highlight the importance of reaction conditions such as temperature and concentration for the reconstitution of chloroplast chaperonin oligomers in vitro.

Mycobacterium tuberculosis GroEL2 Modulates Dendritic Cell Responses

Mycobacterium tuberculosis successfully subverts the host immune response to promote disease progression. In addition to its known intracellular niche in macrophages, M. tuberculosis interferes with the functions of dendritic cells (DCs), which are the primary antigen-presenting cells of the immune system. We previously showed that M. tuberculosis dampens proinflammatory responses and impairs DC functions through the cell envelope-associated serine protease Hip1. Here we present data showing that M. tuberculosis GroEL2, a substrate of Hip1, modulates DC functions. The full-length GroEL2 protein elicited robust proinflammatory responses from DCs and promoted DC maturation and antigen presentation to T cells. In contrast, the cleaved form of GroEL2, which predominates in M. tuberculosis, was poorly immunostimulatory and was unable to promote DC maturation and antigen presentation. Moreover, DCs exposed to full-length, but not cleaved, GroEL2 induced strong antigen-specific gamma interferon (IFN-γ), interleukin-2 (IL-2), and IL-17A cytokine responses from CD4⁺ T cells. Moreover, the expression of cleaved GroEL2 in the hip1 mutant restored the robust T cell responses to wild-type levels, suggesting that proteolytic cleavage of GroEL2 allows M. tuberculosis to prevent optimal DC-T cell cross talk during M. tuberculosis infection.

A structural overview of mycobacterial adhesins: Key biomarkers for diagnostics and therapeutics

Adherence, colonization, and survival of mycobacteria in host cells require surface adhesins, which are attractive pharmacotherapeutic targets. A large arsenal of pilus and non-pilus adhesins have been identified in mycobacteria. These adhesins are capable of interacting with host cells, including macrophages and epithelial cells and are essential to microbial pathogenesis. In the last decade, several structures of mycobacterial adhesins responsible for adhesion to either macrophages or extra cellular matrix proteins have been elucidated. In addition, key structural and functional information have emerged for the process of mycobacterial adhesion to epithelial cells, mediated by the Heparin-binding hemagglutinin (HBHA). In this review, we provide an overview of the structural and functional features of mycobacterial adhesins and discuss their role as important biomarkers for diagnostics and therapeutics. Based on the reported data, it appears clear that adhesins are endowed with a variety of different structures and functions. Most adhesins play important roles in the cell life of mycobacteria and are key virulence factors. However, they have adapted to an extracellular life to exert a role in host-pathogen interaction. The type of interactions they form with the host and the adhesin regions involved in binding is partly known and is described in this review.

GroEL2 of Mycobacterium tuberculosis Reveals the Importance of Structural Pliability in Chaperonin Function

Intracellular protein folding is mediated by molecular chaperones, the best studied among which are the chaperonins GroEL and GroES. Conformational changes and allosteric transitions between different metastable states are hallmarks of the chaperonin mechanism. These conformational transitions between three structural domains of GroEL are anchored at two hinges. Although hinges are known to be critical for mediating the communication between different domains of GroEL, the relative importance of hinges on GroEL oligomeric assembly, ATPase activity, conformational changes, and functional activity is not fully characterized. We have exploited the inability of Mycobacterium tuberculosis GroEL2 to functionally complement an Escherichia coli groEL mutant to address the importance of hinge residues in the GroEL mechanism. Various chimeras of M. tuberculosis GroEL2 and E. coli GroEL allowed us to understand the role of hinges and dissect the consequences of oligomerization and substrate binding capability on conformational transitions. The present study explains the concomitant conformational changes observed with GroEL hinge variants and is best supported by the normal mode analysis.

IMPORTANCE

Conformational changes and allosteric transitions are hallmarks of the chaperonin mechanism. We have exploited the inability of M. tuberculosis GroEL2 to functionally complement a strain of E. coli in which groEL expression is repressed to address the importance of hinges. The significance of conservation at the hinge regions stands out as a prominent feature of the GroEL mechanism in binding to GroES and substrate polypeptides. The hinge residues play a significant role in the chaperonin activity in vivo and in vitro.

Multiple chaperonins in bacteria--novel functions and non-canonical behaviors

Chaperonins are a class of molecular chaperones that assemble into a large double ring architecture with each ring constituting seven to nine subunits and enclosing a cavity for substrate encapsulation. The well-studied Escherichia coli chaperonin GroEL binds non-native substrates and encapsulates them in the cavity thereby sequestering the substrates from unfavorable conditions and allowing the substrates to fold. Using this mechanism, GroEL assists folding of about 10-15 % of cellular proteins. Surprisingly, about 30 % of the bacteria express multiple chaperonin genes. The presence of multiple chaperonins raises questions on whether they increase general chaperoning ability in the cell or have developed specific novel cellular roles. Although the latter view is widely supported, evidence for the former is beginning to appear. Some of these chaperonins can functionally replace GroEL in E. coli and are generally indispensable, while others are ineffective and likewise are dispensable. Additionally, moonlighting functions for several chaperonins have been demonstrated, indicating a functional diversity among the chaperonins. Furthermore, proteomic studies have identified diverse substrate pools for multiple chaperonins. We review the current perception on multiple chaperonins and their physiological and functional specificities.

Mycobacterium tuberculosis adhesins: potential biomarkers as anti-tuberculosis therapeutic and diagnostic targets

Adhesion to host cells is a precursor to host colonization and evasion of the host immune response. Conversely, it triggers the induction of the immune response, a process vital to the host’s defence against infection. Adhesins are microbial cell surface molecules or structures that mediate the attachment of the microbe to host cells and thus the host–pathogen interaction. They also play a crucial role in bacterial aggregation and biofilm formation. In this review, we discuss the role of adhesins in the pathogenesis of the aetiological agent of tuberculosis, Mycobacterium tuberculosis. We also provide insight into the structure and characteristics of some of the characterized and putative M. tuberculosis adhesins. Finally, we examine the potential of adhesins as targets for the development of tuberculosis control strategies.

Mycobacterium tuberculosis Hip1 modulates macrophage responses through proteolysis of GroEL2

Mycobacterium tuberculosis (Mtb) employs multiple strategies to evade host immune responses and persist within macrophages. We have previously shown that the cell envelope-associated Mtb serine hydrolase, Hip1, prevents robust macrophage activation and dampens host pro-inflammatory responses, allowing Mtb to delay immune detection and accelerate disease progression. We now provide key mechanistic insights into the molecular and biochemical basis of Hip1 function. We establish that Hip1 is a serine protease with activity against protein and peptide substrates. Further, we show that the Mtb GroEL2 protein is a direct substrate of Hip1 protease activity. Cleavage of GroEL2 is specifically inhibited by serine protease inhibitors. We mapped the cleavage site within the N-terminus of GroEL2 and confirmed that this site is required for proteolysis of GroEL2 during Mtb growth. Interestingly, we discovered that Hip1-mediated cleavage of GroEL2 converts the protein from a multimeric to a monomeric form. Moreover, ectopic expression of cleaved GroEL2 monomers into the hip1 mutant complemented the hyperinflammatory phenotype of the hip1 mutant and restored wild type levels of cytokine responses in infected macrophages. Our studies point to Hip1-dependent proteolysis as a novel regulatory mechanism that helps Mtb respond rapidly to changing host immune environments during infection. These findings position Hip1 as an attractive target for inhibition for developing immunomodulatory therapeutics against Mtb.

Exploring the role of Mycobacterium avium subspecies paratuberculosis in the pathogenesis of type 1 diabetes mellitus: a pilot study

Background

Although the etiology of Type 1 Diabetes mellitus (T1DM) has not been determined, genetic polymorphism in key genes, including SLC11A1, and association with Mycobacterium avium subspecies paratuberculosis (MAP) have been reported. We hypothesize that molecular mimicry between MAP Heat shock protein 65 K (Hsp65) and human Glutamic Acid Decarboxylase 65 K (GAD65) may be the trigger leading to autoimmune destruction of beta cells in patients exposed to MAP.

Method

Peptide sequences of MAP Hsp65 and human GAD65 were investigated for amino acid sequence homology and cross reactivity. A total of 18 blood samples from T1DM and controls were evaluated for the presence of MAP.

Results

Peptide BLAST analysis revealed a 44% overall identity between MAP Hsp65 and GAD65 with 75% positives in a 16 amino acid region. PyMOL 3D-structural analyses identified the same 16 amino acid region as a potential epitope for antibody binding. Preliminary data suggests a cross reactivity between MAP Hsp65, and a healthy rat pancreatic tissue homogenate against plasma from T1DM patients and rabbit polyclonal anti-MAP IgG. Long-term culture of human blood resulted MAP detection in 3/10 T1DM and 4/8 controls whereas MAP IgG was detected in 5/10 T1DM samples and 3/8 non-diabetic controls.

Conclusion

The high degree of homology between GAD65 and MAP Hsp65 in an antigenic peptide region supports a possible mycobacterial role in triggering autoimmune destruction of pancreatic cells in T1DM. Reactivity of T1DM patient sera with MAP Hsp65 supports this finding. Culture of MAP from the blood of T1DM patients is intriguing. Overall, the preliminary data are mixed and do not exclude a possible role for MAP in T1DM pathogenesis. A larger study including well-characterized controls is needed to investigate the intriguing question of whether MAP is associated with T1DM or not?