Mycobacterium tuberculosis H37Rv enolase (Rv1023)- expression, characterization and effect of host dependent modifications on protein functionality

Mycobacterium tuberculosis enolase is an essential glycolytic enzyme that catalyzes the conversion of 2, phosphoglycerate (PGA) to phosphoenol pyruvate (PEP). It is also a crucial link between glycolysis and the tricarboxylic acid (TCA) pathway. The depletion of PEP has recently been associated with the emergence of non-replicating drug resistant bacteria. Enolase is also known to exhibit multiple alternate functions, such as promoting tissue invasion via its role as a plasminogen (Plg) receptor. In addition, proteomic studies have identified the presence of enolase in the Mtb degradosome and in biofilms. However, the precise role in these processes has not been elaborated. The enzyme was recently identified as a target for 2-amino thiazoles - a novel class of anti-mycobacterials. In vitro assays and characterization of this enzyme were unsuccessful due to the inability to obtain functional recombinant protein. In the present study, we report the expression and characterization of enolase using Mtb H37Ra as a host strain. Our study demonstrates that the enzyme activity and alternate functions of this protein are significantly impacted by the choice of expression host (Mtb H37Ra or E. coli). Detailed analysis of the protein from each source revealed subtle differences in the post-translational modifications. Lastly, our study confirms the role of enolase in Mtb biofilm formation and describes the potential for inhibiting this process.

Regulation of Macrophage Cell Surface GAPDH Alters LL-37 Internalization and Downstream Effects in the Cell

Mycobacterium tuberculosis (M.tb), the major causative agent of tuberculosis, has evolved mechanisms to evade host defenses and persist within host cells. Host-directed therapies against infected cells are emerging as an effective option. Cationic host defense peptide LL-37 is known to internalize into cells and induce autophagy resulting in intracellular killing of M.tb. This peptide also regulates the immune system and interacts with the multifunctional protein glyceraldehyde-3-phosphate dehydrogenase (GAPDH) inside macrophages. Our investigations revealed that GAPDH moonlights as a mononuclear cell surface receptor that internalizes LL-37. We confirmed that the surface levels of purinergic receptor 7, the receptor previously reported for this peptide, remained unaltered on M.tb infected macrophages. Upon infection or cellular activation with IFNγ, surface recruited GAPDH bound to and internalized LL-37 into endocytic compartments via a lipid raft-dependent process. We also discovered a role for GAPDH in LL-37-mediated autophagy induction and clearance of intracellular pathogens. In infected macrophages wherein GAPDH had been knocked down, we observed an inhibition of LL-37-mediated autophagy which was rescued by GAPDH overexpression. This process was dependent on intracellular calcium and p38 MAPK pathways. Our findings reveal a previously unknown process by which macrophages internalize an antimicrobial peptide via cell surface GAPDH and suggest a moonlighting role of GAPDH in regulating cellular phenotypic responses of LL-37 resulting in reduction of M.tb burden.

Mycobacterium tuberculosis glyceraldehyde-3-phosphate dehydrogenase plays a dual role-As an adhesin and as a receptor for plasmin(ogen)

The spread of infection is directly determined by the ability of a pathogen to invade and infect host tissues. The process involves adherence due to host-pathogen interactions and traversal into deeper tissues. Mycobacterium tuberculosis (Mtb) primarily infects the lung but is unique in its ability to infect almost any other organ of the human host including immune privileged sites such as the central nervous system (CNS). The extreme invasiveness of this bacterium is not fully understood. In the current study, we report that cell surface Mtb glyceraldehyde-3-phosphate dehydrogenase (GAPDH) functions as a virulence factor by multiple mechanisms. Firstly, it serves as a dual receptor for both plasminogen (Plg) and plasmin (Plm). CRISPRi-mediated silencing of this essential enzyme confirmed its role in the recruitment of Plg/Plm. Our studies further demonstrate that soluble GAPDH can re-associate on Mtb bacilli to promote plasmin(ogen) recruitment. The direct association of plasmin(ogen) via cell surface GAPDH or by the re-association of soluble GAPDH enhanced bacterial adherence to and traversal across lung epithelial cells. Furthermore, the association of GAPDH with host extracellular matrix (ECM) proteins coupled with its ability to recruit plasmin(ogen) may endow cells with the ability of directed proteolytic activity vital for tissue invasion.

Repurposing ethyl bromopyruvate as a broad-spectrum antibacterial

BACKGROUND

The emergence of drug-resistant bacteria is a major hurdle for effective treatment of infections caused by Mycobacterium tuberculosis and ESKAPE pathogens. In comparison with conventional drug discovery, drug repurposing offers an effective yet rapid approach to identifying novel antibiotics.

METHODS

Ethyl bromopyruvate was evaluated for its ability to inhibit M. tuberculosis and ESKAPE pathogens using growth inhibition assays. The selectivity index of ethyl bromopyruvate was determined, followed by time-kill kinetics against M. tuberculosis and Staphylococcus aureus. We first tested its ability to synergize with approved drugs and then tested its ability to decimate bacterial biofilm. Intracellular killing of M. tuberculosis was determined and in vivo potential was determined in a neutropenic murine model of S. aureus infection.

RESULTS

We identified ethyl bromopyruvate as an equipotent broad-spectrum antibacterial agent targeting drug-susceptible and -resistant M. tuberculosis and ESKAPE pathogens. Ethyl bromopyruvate exhibited concentration-dependent bactericidal activity. In M. tuberculosis, ethyl bromopyruvate inhibited GAPDH with a concomitant reduction in ATP levels and transferrin-mediated iron uptake. Apart from GAPDH, this compound inhibited pyruvate kinase, isocitrate lyase and malate synthase to varying extents. Ethyl bromopyruvate did not negatively interact with any drug and significantly reduced biofilm at a 64-fold lower concentration than vancomycin. When tested in an S. aureus neutropenic thigh infection model, ethyl bromopyruvate exhibited efficacy equal to that of vancomycin in reducing bacterial counts in thigh, and at 1/25th of the dosage.

CONCLUSIONS

Ethyl bromopyruvate exhibits all the characteristics required to be positioned as a potential broad-spectrum antibacterial agent.

Purification and characterization of glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) from pea seeds

Glyceraldehyde-3-phosphate dehydrogenase [GAPDH, NAD + oxidoreductase (phosphorylating) 1.2.1.12] catalyzes the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate coupled with the reduction of NAD(+) to NADH. In addition to its role in glycolysis, this enzyme has numerous alternate functions, in both prokaryotes and eukaryotes. In plants, additional functions have been reported from multiple species including Pisum sativum. A recent study has identified that GAPDH may play an important role in seed ageing and programmed cell death. Despite this the existing purification protocols are almost 40 years old, and only partial characterization of the enzyme has been reported. In the current study, we report a modified method for purification of enzymatically active pea seed GAPDH along with the characterization of the enzyme. Using 2D gel electrophoresis our study also demonstrates that pea seeds contain four isoforms of NAD(+) dependent GAPDH.

Mycobacterium tuberculosis H37Ra: a surrogate for the expression of conserved, multimeric proteins of M.tb H37Rv

BACKGROUND

Obtaining sufficient quantities of recombinant M.tb proteins using traditional approaches is often unsuccessful. Several enzymes of the glycolytic cycle are known to be multifunctional, however relatively few enzymes from M.tb H37Rv have been characterized in the context of their enzymatic and pleiotropic roles. One of the primary reasons is the difficulty in obtaining sufficient amounts of functionally active protein.

RESULTS

In the current study, using M.tb glyceraldehyde-3-phosphate dehydrogenase (GAPDH) we demonstrate that expression in E. coli or M. smegmatis results in insolubility and improper subcellular localization. In addition, expression of such conserved multisubunit proteins poses the problem of heteromerization with host homologues. Importantly the expression host dramatically affected the yield and functionality of GAPDH in terms of both enzymatic activity and moonlighting function (transferrin binding). The applicability of this system was further confirmed using two additional enzymes i.e. M.tb Pyruvate kinase and Enolase.

CONCLUSIONS

Our studies establish that the attenuated strain M.tb H37Ra is a suitable host for the expression of highly hydrophobic, conserved, multimeric proteins of M.tb H37Rv. Significantly, this expression host overcomes the limitations of E. coli and M. smegmatis expression and yields recombinant protein that is qualitatively superior to that obtained by traditional methods. The current study highlights the fact that protein functionality (which is an an essential requirement for all in vitro assays and drug development) may be altered by the choice of expression host.

Reverse overshot water-wheel retroendocytosis of apotransferrin extrudes cellular iron

Iron (Fe), a vital micronutrient for all organisms, must be managed judiciously because both deficiency or excess can trigger severe pathology. Although cellular Fe import is well understood, its export is thought to be limited to transmembrane extrusion through ferroportin (also known as Slc40a1), the only known mammalian Fe exporter. Utilizing primary cells and cell lines (including those with no discernible expression of ferroportin on their surface), we demonstrate that upon Fe loading, the multifunctional enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which is recruited to the cell surface, 'treadmills' apotransferrin in and out of the cell. Kinetic analysis utilizing labeled ligand, GAPDH-knockdown cells, (55)Fe-labeled cells and pharmacological inhibitors of endocytosis confirmed GAPDH-dependent apotransferrin internalization as a prerequisite for cellular Fe export. These studies define an unusual rapid recycling process of retroendocytosis for cellular Fe extrusion, a process mirroring receptor mediated internalization that has never before been considered for maintenance of cellular cationic homeostasis. Modulation of this unusual pathway could provide insights for management of Fe overload disorders.