Cells on the move: Modulation of guidance cues during germ cell migration

In Drosophila melanogaster the progenitors of the germ-line stem cells, the primordial germ cells (PGCs) are formed on the outside surface of the early embryo, while the somatic gonadal precursor cells (SGPs) are specified during mid-embryogenesis. To form the primitive embryonic gonad, the PGCs travel from outside of the embryo, across the mid-gut and then migrate through the mesoderm to the SGPs. The migratory path of PGCs is dictated by a series of attractive and repulsive cues. Studies in our laboratory have shown that one of the key chemoattractants is the Hedgehog (Hh) ligand. Although, Hh is expressed in other cell types, the long-distance transmission of this ligand is specifically potentiated in the SGPs by the hmgcr isoprenoid biosynthetic pathway. The distant transmission of the Hh ligand is gated by restricting expression of hmgcr to the SGPs. This is particularly relevant in light of the recent findings that an ABC transporter, mdr49 also acts in a mesoderm specific manner to release the germ cell attractant. Our studies have demonstrated that mdr49 functions in hh signaling likely via its role in the transport of cholesterol. Given the importance of cholesterol in the processing and long distance transmission of the Hh ligand, this observation has opened up an exciting avenue concerning the possible role of components of the sterol transport machinery in PGC migration.     

Study of fluorescence interaction and conformational changes of bovine serum albumin with histamine H1‐receptor–drug epinastine hydrochloride by spectroscopic and time‐resolved fluorescence methods

The fluorescence, ultraviolet (UV) absorption, time resolved techniques, circular dichroism (CD), and infrared spectral methods were explored as tools to investigate the interaction between histamine H₁ drug, epinastine hydrochloride (EPN), and bovine serum albumin (BSA) under simulated physiological conditions. The experimental results showed that the quenching of the BSA by EPN was static quenching mechanism and also confirmed by lifetime measurements. The value of n close to unity indicated that one molecule of EPN was bound to protein molecule. The binding constants (K) at three different temperatures were calculated (7.1 × 10⁴, 5.5 × 10⁴, and 3.9 × 10⁴M⁻¹). Based on the thermodynamic parameters (ΔH⁰, ΔG⁰, and ΔS⁰), the nature of binding forces operating between drug and protein was proposed. The site of binding of EPN in the protein was proposed to be Sudlow's site I based on displacement experiments using site markers viz, warfarin, ibuprofen, and digitoxin. Based on the Förster's theory of non‐radiation energy transfer, the binding average distance, r between the donor (BSA) and acceptor (EPN) was evaluated and found to be 4.48 nm. The UV–visible, synchronous fluorescence, CD, and three‐dimensional fluorescence spectral results revealed the changes in secondary structure of the protein upon its interaction with EPN. © 2015 Wiley Periodicals, Inc. Biopolymers 103: 646–657, 2015.     

Connections between sphingosine kinase and phospholipase D in the abscisic acid signaling pathway in Arabidopsis

Phosphatidic acid (PA) and phytosphingosine 1-phosphate (phyto-S1P) both are lipid messengers involved in plant response to abscisic acid (ABA). Our previous data indicate that PA binds to sphingosine kinase (SPHK) and increases its phyto-S1P-producing activity. To understand the cellular and physiological functions of the PA-SPHK interaction, we isolated Arabidopsis thaliana SPHK mutants sphk1-1 and sphk2-1 and characterized them, together with phospholipase Dα1 knock-out, pldα1, in plant response to ABA. Compared with wild-type (WT) plants, the SPHK mutants and pldα1 all displayed decreased sensitivity to ABA-promoted stomatal closure. Phyto-S1P promoted stomatal closure in sphk1-1 and sphk2-1, but not in pldα1, whereas PA promoted stomatal closure in sphk1-1, sphk2-1, and pldα1. The ABA activation of PLDα1 in leaves and protoplasts was attenuated in the SPHK mutants, and the ABA activation of SPHK was reduced in pldα1. In response to ABA, the accumulation of long-chain base phosphates was decreased in pldα1, whereas PA production was decreased in SPHK mutants, compared with WT. Collectively, these results indicate that SPHK and PLDα1 act together in ABA response and that SPHK and phyto-S1P act upstream of PLDα1 and PA in mediating the ABA response. PA is involved in the activation of SPHK, and activation of PLDα1 requires SPHK activity. The data suggest that SPHK/phyto-S1P and PLDα1A are co-dependent in amplification of response to ABA, mediating stomatal closure in Arabidopsis.     

A novel pyrimidine derivatives with aryl urea, thiourea and sulfonamide moieties: synthesis, anti-inflammatory and antimicrobial evaluation

A series of novel 4-(3-(trifluoromethyl)phenylamino-6-(4-(3-arylureiodo/arylthioureido/arylsulfonamido)-pyrimidine derivatives of biological interest were prepared by the sequential Suzuki cross coupling, acid amination, reduction followed by reaction of resulting amine with different arylisocyantes or arylisothiocyantes or arylsulfonyl chlorides. All the synthesized compounds (1-25) were screened for their pro-inflammatory cytokines (TNF-α and IL-6) and antimicrobial activity (antibacterial and antifungal). Biological data revealed that among all the compounds screened, compounds 5, 6, 11, 12, 16 and 20 were found to have moderate to potent anti-inflammatory activity (up to 48-78% TNF-α and 56-96% IL-6 inhibitory activity) with reference to standard dexamethasone at 10 μM. The compounds 10, 12, 13, 18, 20, 22, 24 and 25 found to have promising antimicrobial activity against all the selected pathogenic bacteria and fungi.     

Polymeric black tea polyphenols modulate the localization and activity of 12-O-tetradecanoylphorbol-13-acetate-mediated kinases in mouse skin: Mechanisms of their anti-tumor-promoting action

Polymeric black tea polyphenols (PBPs) have been shown to possess anti-tumor-promoting effects in two-stage skin carcinogenesis. However, their mechanisms of action are not fully elucidated. In this study, mechanisms of PBP-mediated antipromoting effects were investigated in a mouse model employing the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Compared to controls, a single topical application of TPA to mouse skin increased the translocation of protein kinase C (PKC) from cytosol to membrane. Pretreatment with PBPs 1-3 decreased TPA-induced translocation of PKC isozymes (α, β, η, γ, ε) from cytosol to membrane, whereas PBPs 4 and 5 were less effective. The levels of PKCs δ and ζ in cytosol/membrane were similar in all the treatment groups. Complementary confocal microscopic evaluation showed a decrease in TPA-induced PKCα fluorescence in PBP-3-pretreated membranes, whereas pretreatment with PBP-5 did not show a similar decrease. Based on the experiments with specific enzyme inhibitors and phosphospecific antibodies, both PBP-3 and PBP-5 were observed to decrease TPA-induced level and/or activity of phosphatidylinositol 3-kinase (PI3K) and AKT1 (pS473). An additional ability of PBP-3 to inhibit site-specific phosphorylation of PKCα at all three positions responsible for its activation [PKCα (pT497), PKC PAN (βII pS660), PKCα/βII (pT638/641)] and AKT1 at the Thr308 position, along with a decrease in TPA-induced PDK1 protein level, correlated with the inhibition of translocation of PKC, which may impart relatively stronger chemoprotective activity to PBP-3 than to PBP-5. Altogether, PBP-mediated decrease in TPA-induced PKC phosphorylation correlated well with decreased TPA-induced NF-κB phosphorylation and downstream target proteins associated with proliferation, apoptosis, and inflammation in mouse skin. Results suggest that the antipromoting effects of PBPs are due to modulation of TPA-induced PI3K-mediated signal transduction.     

Snake venom hyaluronidase: a therapeutic target

The diffusion of toxins from the site of a bite into the circulation is essential for successful envenomation. Degradation of hyaluronic acid in the extracellular matrix (ECM) by venom hyaluronidase is a key factor in this diffusion. Hyaluronidase not only increases the potency of other toxins but also damages the local tissue. In spite of its important role, little attention has been paid to this enzyme. Hyaluronidase exists in various isoforms and generates a wide range of hyaluronic acid degradation products. This suggests that beyond its role as a spreading factor venom hyaluronidase deserves to be explored as a possible therapeutic target for inhibiting the systemic distribution of venom and also for minimizing local tissue destruction at the site of the bite.     

Desaturases: Emerging Models for Understanding Functional Diversification of Diiron-containing Enzymes

Desaturases and related enzymes perform O₂-dependent dehydrogenations initiated at unactivated C-H groups with the use of a diiron active site. Determination of the long-sought oxidized desaturase crystal structure facilitated structural comparison of the active sites of disparate diiron enzymes. Experiments on the castor desaturase are discussed that provide experimental support for a hypothesized ancestral oxidase enzyme in the context of the evolution of the diiron enzyme diverse functionality. We also summarize recent analysis of a castor mutant desaturase that provides valuable insights into the relationship of proposed substrate-binding modes with respect to a range of catalytic outcomes.Desaturase enzymes perform dehydrogenation reactions that result in the introduction of double bonds into fatty acids that are initiated by the energy-demanding abstraction of a hydrogen from a methylene group (1–3). To achieve this, desaturase enzymes recruit and activate molecular oxygen with the use of an active-site diiron cluster (4). The diiron center is common to a variety of proteins, including methane monooxygenase, ribonucleotide reductase, rubrerythrins, and a variety of oxidase enzymes (5). Valuable insights regarding the tuning of diiron centers with respect to diverse chemical reactivity (6) have been made via comparisons of the diiron centers of diiron-containing enzymes (7); however, differences in amino acid sequence, multiple protein-protein interactions, and reaction outcomes complicate the analysis. The study of fatty-acid desaturases and related enzymes presents a unique opportunity for performing enzyme structure-function studies because relatively close homologs perform diverse reactions on similar substrates (8, 9).Desaturase enzymes have evolved independently twice (10); the acyl-ACP² desaturases are soluble enzymes found in the plastids of higher plants, whereas the more widespread class of integral membrane desaturases is found in endomembrane systems in prokaryotes and eukaryotes (9). In addition to forming distinct homology groups, their diiron centers possess distinct primary ligation spheres (11). The availability of crystal structures for acyl-ACP desaturases (12) makes this system amenable to detailed structure-function studies. Crystal structures are available for the 18:0 Δ⁹-desaturase³ (12, 13) from Ricinus communis (castor) and a bifunctional desaturase from Hedera helix (ivy) (14, 15). These desaturases are homodimeric proteins, with each monomer folded into a compact single domain composed of nine helices. The diiron active site of these enzymes is buried within a core four-helix bundle and is positioned alongside a deep, bent, narrow hydrophobic cavity in which the substrate is bound during catalysis. It is a textbook example of a lock-and-key type of binding site in which the bound fatty acid moiety is poised for formation of the cis-fatty acid product.Nobel Laureate Konrad Bloch observed, “The stereospecific removal of hydrogen in the formation of oleate, although predictable on principle grounds would seem to approach the limits of the discriminatory power of enzymes” (16). Bloch''s statement underscores that desaturase enzymes perform highly regio- and stereo-selective reactions on long-chain fatty acids composed of essentially equivalent methylene chains that lack distinguishing landmarks close to the site of desaturation. We will review structural features of the diiron active site of the acyl-ACP desaturases in the context of those of other diiron enzymes, discuss recent insights into the evolution of acyl-ACP desaturases, and summarize recent discoveries relating to the evolution of selectivity and functional diversity within desaturase enzyme families.