Structural and biochemical characterization of Rv2140c, a phosphatidylethanolamine-binding protein from Mycobacterium tuberculosis

Florigen and its homologs of FT/CETS/PEBP/RKIP/YbhB family may be the enzymes of small molecule metabolism: review of the evidence

BACKGROUND

Flowering signals are sensed in plant leaves and transmitted to the shoot apical meristems, where the formation of flowers is initiated. Searches for a diffusible hormone-like signaling entity ("florigen") went on for many decades, until a product of plant gene FT was identified as the key component of florigen in the 1990s, based on the analysis of mutants, genetic complementation evidence, and protein and RNA localization studies. Sequence homologs of FT protein are found throughout prokaryotes and eukaryotes; some eukaryotic family members appear to bind phospholipids or interact with the components of the signal transduction cascades. Most FT homologs are known to share a constellation of five charged residues, three of which, i.e., two histidines and an aspartic acid, are located at the rim of a well-defined cavity on the protein surface.

RESULTS

We studied molecular features of the FT homologs in prokaryotes and analyzed their genome context, to find tentative evidence connecting the bacterial FT homologs with small molecule metabolism, often involving substrates that contain sugar or ribonucleoside moieties. We argue that the unifying feature of this protein family, i.e., a set of charged residues conserved at the sequence and structural levels, is more likely to be an enzymatic active center than a catalytically inert ligand-binding site.

CONCLUSIONS

We propose that most of FT-related proteins are enzymes operating on small diffusible molecules. Those metabolites may constitute an overlooked essential ingredient of the florigen signal.

Mycobacterium tuberculosis RKIP (Rv2140c) dephosphorylates ERK/NF-κB upstream signaling molecules to subvert macrophage innate immune response

Mycobacterium tuberculosis (Mtb) survival and virulence largely reside on its ability to manipulate the host immune response. We have previously shown that M. tuberculosis Raf kinase inhibitor protein (RKIP) Rv2140c regulates diverse phosphorylation events in M. smegmatis. However, its role during infection is unknown. In this report, we show that Rv2140c can mimic the mammalian RKIP function. Rv2140c inhibit the activation of extracellular signal-regulated kinase (ERK) and nuclear factor κB (NF-κB) via decreasing the phosphorylation capacity of upstream mediators MEK1, ERK1/2, and IKKα/β, thus leading to a reduction in pro-inflammatory cytokines IL-1β, IL-6, and TNF-α. This effect can be reversed by RKIP inhibitor locostatin. Furthermore Rv2140c mediates apoptosis associated with activation of caspases cascades. This modulation enhances the intracellular survival of M. smegmatis within macrophage. We propose that Rv2140c is a multifunctional virulence factor and a promising novel anti-Tuberculosis drug target.

Mycobacterium tuberculosis Raf kinase inhibitor protein (RKIP) Rv2140c is involved in cell wall arabinogalactan biosynthesis via phosphorylation

Mycobacterium tuberculosis Rv2140c is a function unknown conserved phosphatidylethanolamine-binding protein (PEBP), homologous to Raf kinase inhibitor protein (RKIP) in human beings. To delineate its function, we heterologously expressed Rv2140c in a non-pathogenic M. smegmatis. Quantitative phosphoproteomic analysis between two recombinant strains Ms_Rv2140c and Ms_vec revealed that Rv2140c differentially regulate 425 phosphorylated sites representing 282 proteins. Gene ontology GO, and a cluster of orthologous groups COG analyses showed that regulated phosphoproteins by Rv2140c were mainly associated with metabolism and cellular processes. Rv2140c significantly repressed phosphoproteins involved in signaling, including serine/threonine-protein kinases and two-component system, and the arabinogalactan biosynthesis pathway phosphoproteins were markedly up-regulated, suggesting a role of Rv2140c in modulating cell wall. Consistent with phosphoproteomic data, Rv2140c altered some phenotypic properties of M. smegmatis such as colony morphology, cell wall permeability, survival in acidic conditions, and active lactose transport. In summary, we firstly demonstrated the role of PEBP protein Rv2140c, especially in phosphorylation of mycobacterial arabinogalactan biosynthesis proteins.

Secretory Proteome Analysis of Streptomycin-Resistant Mycobacterium tuberculosis Clinical Isolates

Tuberculosis still remains one of the most fatal infectious diseases. Streptomycin (SM) is the drug of choice, especially for patients with multidrug-resistant tuberculosis or category II patients, because it targets the protein synthesis machinery by interacting with steps of translation. Several mechanisms have been proposed to explain the resistance, but our knowledge is inadequate. Secretome often plays an important role in pathogenesis and is considered an attractive reservoir for the development of novel diagnostic markers and targets. In this study, we analyze the secretory proteins of streptomycin-resistant Mycobacterium tuberculosis isolates by 2-dimensional gel electrophoresis-matrix assisted laser desorption/ionization-time-of-flight mass spectrometry and bioinformatic tools. Fifteen overexpressed proteins were identified in a resistant isolate that belonged to various categories such as virulence/detoxification/adaptation, intermediary metabolism and respiration, and conserved hypotheticals. Among them, Rv1860, Rv1980c, Rv2140c, Rv1636, and Rv1926c were proteins of an undefined role. Molecular docking of these proteins with SM showed that it binds to their conserved domains and suggests that these might neutralize/compensate the effect of the drug. The interactome also suggests that overexpressed proteins along with their interactive partner might be involved in M. tuberculosis virulence and resistance. The cumulative effect of these overexpressed proteins could involve SM resistance, and these might be used as diagnostic markers or potential drug targets.

Cytosolic Proteome Profiling of Aminoglycosides Resistant Mycobacterium tuberculosis Clinical Isolates Using MALDI-TOF/MS

Emergence of extensively drug resistant tuberculosis (XDR-TB) is the consequence of the failure of second line TB treatment. Aminoglycosides are the important second line anti-TB drugs used to treat the multi drug resistant tuberculosis (MDR-TB). Main known mechanism of action of aminoglycosides is to inhibit the protein synthesis by inhibiting the normal functioning of ribosome. Primary target of aminoglycosides are the ribosomal RNA and its associated proteins. Various mechanisms have been proposed for aminoglycosides resistance but still some are unsolved. As proteins are involved in most of the biological processes, these act as a potential diagnostic markers and drug targets. In the present study we analyzed the purely cytosolic proteome of amikacin (AK) and kanamycin (KM) resistant Mycobacterium tuberculosis isolates by proteomic and bioinformatic approaches. Twenty protein spots were found to have over expressed in resistant isolates and were identified. Among these Rv3208A, Rv2623, Rv1360, Rv2140c, Rv1636, and Rv2185c are six proteins with unknown functions or undefined role. Docking results showed that AK and KM binds to the conserved domain (DUF, USP-A, Luciferase, PEBP and Polyketidecyclase/dehydrase domain) of these hypothetical proteins and over expression of these proteins might neutralize/modulate the effect of drug molecules. TBPred and GPS-PUP predicted cytoplasmic nature and potential pupylation sites within these identified proteins, respectively. String analysis also suggested that over expressed proteins along with their interactive partners might be involved in aminoglycosides resistance. Cumulative effect of these over expressed proteins could be involved in AK and KM resistance by mitigating the toxicity, repression of drug target and neutralizing affect. These findings need further exploitation for the expansion of newer therapeutics or diagnostic markers against AK and KM resistance so that an extreme condition like XDR-TB can be prevented.