Paraveinal mesophyll: Review and survey of the subtribeErythrininae (Phaseoleae,Papilionoideae, Leguminosae)

Paraveinal mesophyll (PVM) is a distinctive anatomical feature of the leaf mesophyll of some plant taxa that may represent a specialized physiological compartment. A comprehensive review of the 42 published references that mention PVM or similar cell layers and a survey of 121 of the 272 species of all nine genera of thePhaseoleae subtribeErythrininae demonstrate that PVM is nearly exclusively found inLeguminosae. InLeguminosae, PVM is either rare or absent in subfamilyCaesalpinioideae, uncommon inMimosoideae, and extensively distributed amongPapilionoideae. In subtribeErythrininae, PVM is ubiquitous inErythrina, and occurs in four other genera. ThreeErythrininae genera (Apios, Mucuna, andCochlianthus) lack PVM. Unique chloroplast-poor, enlarged conical cells (pellucid palisade idioblasts) occur in 80 species ofErythrina but not in any other genus ofErythrininae.     

Structural insights into pharmacophore-assisted in silico identification of protein–protein interaction inhibitors for inhibition of human toll-like receptor 4 – myeloid differentiation factor-2 (hTLR4−MD-2) complex

Toll-like receptor 4 (TLR4) is a member of Toll-Like Receptors (TLRs) family that serves as a receptor for bacterial lipopolysaccharide (LPS). TLR4 alone cannot recognize LPS without aid of co-receptor myeloid differentiation factor-2 (MD-2). Binding of LPS with TLR4 forms a LPS?TLR4?MD-2 complex and directs downstream signaling for activation of immune response, inflammation and NF-κB activation. Activation of TLR4 signaling is associated with various pathophysiological consequences. Therefore, targeting protein–protein interaction (PPI) in TLR4?MD-2 complex formation could be an attractive therapeutic approach for targeting inflammatory disorders. The aim of present study was directed to identify small molecule PPI inhibitors (SMPPIIs) using pharmacophore mapping-based approach of computational drug discovery. Here, we had retrieved the information about the hot spot residues and their pharmacophoric features at both primary (TLR4?MD-2) and dimerization (MD-2?TLR4*) protein–protein interaction interfaces in TLR4?MD-2 homo-dimer complex using in silico methods. Promising candidates were identified after virtual screening, which may restrict TLR4?MD-2 protein–protein interaction. In silico off-target profiling over the virtually screened compounds revealed other possible molecular targets. Two of the virtually screened compounds (C11 and C15) were predicted to have an inhibitory concentration in μM range after HYDE assessment. Molecular dynamics simulation study performed for these two compounds in complex with target protein confirms the stability of the complex. After virtual high throughput screening we found selective hTLR4?MD-2 inhibitors, which may have therapeutic potential to target chronic inflammatory diseases.     

Microcystins: Synthesis and structure–activity relationship studies toward PP1 and PP2A

Microcystins are highly toxic cyanotoxins responsible for plant, animal and human poisoning. Exposure to microcystins, mainly through drinkable water and contaminated food, is a current world health concern. Although it is quite challenging, the synthesis of these potent cyanotoxins, analogs and derivatives helps to evaluate their toxicological properties and to elucidate their binding mechanisms to their main targets Protein Phosphatase-1 (PP1) and -2A (PP2A). This review focuses on synthetic approaches to prepare microcystins and analogs and compiles structure–activity relationship (SAR) studies that describe the unique features of microcystins that make them so potent.     

The interactions of molecular chaperones with client proteins: why are they so weak?

The major classes of molecular chaperones have highly variable sequences, sizes, and shapes, yet they all bind to unfolded proteins, limit their aggregation, and assist in their folding. Despite the central importance of this process to protein homeostasis, it has not been clear exactly how chaperones guide this process or whether the diverse families of chaperones use similar mechanisms. For the first time, recent advances in NMR spectroscopy have enabled detailed studies of how unfolded, “client” proteins interact with both ATP-dependent and ATP-independent classes of chaperones. Here, we review examples from four distinct chaperones, Spy, Trigger Factor, DnaK, and HscA-HscB, highlighting the similarities and differences between their mechanisms. One striking similarity is that the chaperones all bind weakly to their clients, such that the chaperone–client interactions are readily outcompeted by stronger, intra- and intermolecular contacts in the folded state. Thus, the relatively weak affinity of these interactions seems to provide directionality to the folding process. However, there are also key differences, especially in the details of how the chaperones release clients and how ATP cycling impacts that process. For example, Spy releases clients in a largely folded state, while clients seem to be unfolded upon release from Trigger Factor or DnaK. Together, these studies are beginning to uncover the similarities and differences in how chaperones use weak interactions to guide protein folding.     

Global profiling of protein complexes: current approaches and their perspective in biomedical research

Introduction: Despite the rapid evolution of proteomic methods, protein interactions and their participation in protein complexes – an important aspect of their function – has rarely been investigated on the proteome-wide level. Disease states, such as muscular dystrophy or viral infection, are induced by interference in protein-protein interactions within complexes. The purpose of this review is to describe the current methods for global complexome analysis and to critically discuss the challenges and opportunities for the application of these methods in biomedical research.

Areas covered: We discuss advancements in experimental techniques and computational tools that facilitate profiling of the complexome. The main focus is on the separation of native protein complexes via size exclusion chromatography and gel electrophoresis, which has recently been combined with quantitative mass spectrometry, for a global protein-complex profiling. The development of this approach has been supported by advanced bioinformatics strategies and fast and sensitive mass spectrometers that have allowed the analysis of whole cell lysates. The application of this technique to biomedical research is assessed, and future directions are anticipated.

Expert commentary: The methodology is quite new, and has already shown great potential when combined with complementary methods for detection of protein complexes.     

Development and validation of a Sensitive bioanalytical method for the quantitative estimation of Pantoprazole in human plasma samples by LC–MS/MS: Application to bioequivalence study

The present study aims at developing a simple, sensitive and specific liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the quantification of pantoprazole sodium (PS) in human plasma using pantoprazole D3 (PSD3) as internal standard (IS). Chromatographic separation was performed on Zorbax SB-C18, 4.6 mm × 75 mm, 3.5 μm, 80 Å column with an isocratic mobile phase composed of 10 mM ammonium acetate (pH 7.10): acetonitrile (30:70, v/v), pumped at 0.6 mL/min. PS and PSD3 were detected with proton adducts at m/z 384.2 → 200.1 and 387.1 → 203.1 in multiple reaction monitoring (MRM) positive mode, respectively. Precipitation method was employed in the extraction of PS and PSD3 from the biological matrix. This method was validated over a linear concentration range of 10.00–3000.00 ng/mL with correlation coefficient (r) ≥ 0.9997. Intra- and inter-day precision of PS were found to be within the range of 1.13–1.54 and 1.76–2.86, respectively. Both analytes were stable throughout freeze/thaw cycles, bench top and postoperative stability studies. This method was successfully utilized in the analysis of blood samples following oral administration of PS (40 mg) in healthy human volunteers.     

Thermodynamic and structural analysis of homodimeric proteins: Model of β-lactoglobulin

The energetics of protein homo-oligomerization was analyzed in detail with the application of a general thermodynamic model. We have studied the thermodynamic aspects of protein-protein interaction employing β-lactoglobulin A from bovine milk at pH = 6.7 where the protein is mainly in its dimeric form. We performed differential calorimetric scans at different total protein concentration and the resulting thermograms were analyzed with the thermodynamic model for oligomeric proteins previously developed. The thermodynamic model employed, allowed the prediction of the sign of the enthalpy of dimerization, the analysis of complex calorimetric profiles without transitions baselines subtraction and the obtainment of the thermodynamic parameters from the unfolding and the association processes and the compared with association parameters obtained with Isothermal Titration Calorimetry performed at different temperatures. The dissociation and unfolding reactions were also monitored by Fourier-transform infrared spectroscopy and the results indicated that the dimer of β-lactoglobulin (N₂) reversibly dissociates into monomeric units (N) which are structurally distinguishable by changes in their infrared absorbance spectra upon heating. Hence, it is proposed that β-lactoglobulin follows the conformational path induced by temperature:N₂ ? 2N ? 2D. The general model was validated with these results indicating that it can be employed in the study of the thermodynamics of other homo-oligomeric protein systems.     

Advances in inhibition of protein-protein interactions targeting hypoxia-inducible factor-1 for cancer therapy

Hypoxia is a common characteristic of many types of solid tumors and is associated with tumor propagation, malignant progression, and resistance to anti-cancer therapy. HIF-1 pathway is one of the survival pathways activated in tumor in response to hypoxia. In hypoxic condition, hypoxia-inducible factor-1α (HIF-1α) is stabilized and translocated into nucleus where it forms heterodimer with HIF-1β and regulates the expression of a plethora of genes involved in different processes, such as cell proliferation, differentiation, apoptosis, vascularization/angiogenesis, tumor invasion and metastasis. Recruitment of co-activator p300 or CBP to HIF-1α is critical to the transactivation activity of HIF-1 dimer, therefore, small molecules which can block the dimerization of HIF-1α and HIF-1β or inhibit the interaction between HIF-1α and p300 can function as inhibitors of HIF-1 and have the potential to be developed as novel therapies for the treatment of human cancers. In this review, recent progress of small molecular inhibitors of protein-protein interactions targeting HIF-1 is summarized, the mechanism of functions of these compounds and their potential usage as anti-cancer agents have also been discussed.