Mycosporine-like amino acids (MAAs): chemical structure, biosynthesis and significance as UV-absorbing/screening compounds

Continuous depletion of the stratospheric ozone layer has resulted in an increase in ultraviolet-B (UV-B; 280-315 nm) radiation on the earth's surface which inhibits photochemical and photobiological processes. However, certain photosynthetic organisms have evolved mechanisms to counteract the toxicity of ultraviolet or high photosynthetically active radiation by synthesizing the UV-absorbing/screening compounds, such as mycosporine-like amino acids (MAAs) and scytonemin besides the repair of UV-induced damage of DNA and accumulation of carotenoids and detoxifying enzymes or radical quenchers and antioxidants. Chemical structure of various MAAs, their possible biochemical routes of synthesis and role as photoprotective compounds in various organisms are discussed.     

Structure and function of LGP2, a DEX(D/H) helicase that regulates the innate immunity response

RNA recognition receptors are important for detection of and response to viral infections. RIG-I and MDA5 are cytoplasmic DEX(D/H) helicase proteins that can induce signaling in response to RNA ligands, including those from viral infections. LGP2, a homolog of RIG-I and MDA5 without the caspase recruitment domain required for signaling, plays an important role in modulating signaling by MDA5 and RIG-I, presumably through heterocomplex formation and/or by serving as a sink for RNAs. Here we demonstrate that LGP2 can be coexpressed with RIG-I to inhibit activation of the NF-kappaB reporter expression and that LGP2 protein produced in insect cells can bind both single- and double-stranded RNA (dsRNA), with higher affinity and cooperativity for dsRNA. Electron microscopy and image reconstruction were used to determine the shape of the LGP2 monomer in the absence of dsRNA and of the dimer complexed to a 27-bp dsRNA. LGP2 has striking structural similarity to the helicase domain of the superfamily 2 DNA helicase, Hef.     

Correlation of Plasma Dopamine β-hydroxylase Activity with Polymorphisms in DBH Gene: A Study on Eastern Indian Population

Plasma dopamine β-hydroxylase activity (plDβH) is tightly regulated by the DBH gene and several genetic polymorphisms have been found to independently exert their influence. In the present investigation, association of four DBH polymorphisms, DBH-STR, rs1611115, rs1108580, and rs2519152 with plDβH was examined in blood samples from 100 unrelated individuals belonging to the state of West Bengal, Eastern India. Genotypes obtained after PCR amplification and restriction digestion were used for statistical analyses. plDβH was measured using a photometric assay and its correlation with the genetic polymorphisms was analyzed using analysis of variance and linear regression. Moderate linkage disequilibrium (LD) was observed between DBH-STR and rs1611115, while rs1108580 and rs2519152 were in strong LD. ‘T’ allele of rs1611115 showed strong negative correlation with plDβH, whereas DBH-STR, rs1108580 and rs2519152 had no major effect. Four haplotypes showed significant influence on plDβH. This is the first report on the effect of genetic polymorphisms on plDβH from the Indian sub-continent. rs1611115 was the only polymorphism that showed substantial control over plDβH. Other polymorphisms which did not show individual effects could possibly be part of larger haplotype blocks that carry the functional polymorphisms controlling plDβH. Part of this work was presented at an international conference “NEURODEGENERATION AND NEUROPROTECTION” held at Kolkata, India during Jan 8th–9th, 2007.     

RNA recognition and cleavage by the SARS coronavirus endoribonuclease

The emerging disease SARS is caused by a novel coronavirus that encodes several unusual RNA-processing enzymes, including non-structural protein 15 (Nsp15), a hexameric endoribonuclease that preferentially cleaves at uridine residues. How Nsp15 recognizes and cleaves RNA is not well understood and is the subject of this study. Based on the analysis of RNA products separated by denaturing gel electrophoresis, Nsp15 has been reported to cleave both 5' and 3' of the uridine. We used several RNAs, including some with nucleotide analogs, and mass spectrometry to determine that Nsp15 cleaves only 3' of the recognition uridylate, with some cleavage 3' of cytidylate. A highly conserved RNA structure in the 3' non-translated region of the SARS virus was cleaved preferentially at one of the unpaired uridylate bases, demonstrating that both RNA structure and base-pairing can affect cleavage by Nsp15. Several modified RNAs that are not cleaved by Nsp15 can bind Nsp15 as competitive inhibitors. The RNA binding affinity of Nsp15 increased with the content of uridylate in substrate RNA and the co-factor Mn(2+). The hexameric form of Nsp15 was found to bind RNA in solution. A two-dimensional crystal of Nsp15 in complex with RNA showed that at least two RNA molecules could be bound per hexamer. Furthermore, an 8.3 A structure of Nsp15 was developed using cyroelectron microscopy, allowing us to generate a model of the Nsp15-RNA complex.     

Long-term hypoxia modulates expression of key genes regulating adipose function in the late-gestation ovine fetus

A major function of abdominal adipose in the newborn is nonshivering thermogenesis. Uncoupling protein (UCP) UCP1 and UCP2 play major roles in thermogenesis. The present study tested the hypothesis that long-term hypoxia (LTH) modulates expression of UCP1 and UCP2, and key genes regulating expression of these genes in the late-gestation ovine fetus. Ewes were maintained at high altitude (3,820 m) from 30 to 138 days gestation (dG); perirenal adipose tissue was collected from LTH and age-matched, normoxic control fetuses at 139-141 dG. Quantitative real-time PCR was used to analyze mRNA for UCP1, UCP2, 11beta hydroxysteroid dehydrogenase type 1 (HSD11B1) and 2 (HSD11B2), glucocorticoid receptor (GR), beta3 adrenergic receptor (beta3AR), deiodinase type 1 (DIO1) and DIO2, peroxisome proliferator activated receptor (PPAR) alpha and gamma and PPARgamma coactivator 1 (PGC1alpha). Concentrations of mRNA for UCP1, HSD11B1, PPARgamma, PGC1, DIO1, and DIO2 were significantly higher in perirenal adipose of LTH compared with control fetuses, while mRNA for HSD11B2, GR, or PPARalpha in perirenal adipose did not differ between control and LTH fetuses. The increased expression of UCP1 is likely an adaptive response to LTH, assuring adequate thermogenesis in the event of birth under oxygen-limiting conditions. Because both glucocorticoids and thyroid hormone regulate UCP1 expression, the increase in HSD11B1, DIO1, and DIO2 implicate increased adipose capacity for local synthesis of these hormones. PPARgamma and its coactivator may provide an underlying mechanism via which LTH alters development of the fetal adipocyte. These findings have important implications regarding fetal/neonatal adipose tissue function in response to LTH.     

Erectile dysfunction in the type II diabetic db/db mouse: impaired venoocclusion with altered cavernosal vasoreactivity and matrix

The number of men with type II diabetes-associated erectile dysfunction (ED) continues to grow rapidly; however, the majority of basic science studies has examined mechanisms of ED in animal models of type I diabetes. In this study, we first establish an in vivo mouse model of type II diabetic ED using the leptin receptor mutated db/db and wild-type control BKS mouse. Furthermore, we hypothesized that dual mechanistic impairments contribute to the impaired erectile function in the type II diabetic mouse, altered vasoreactivity, and venoocclusive disorder. In vivo erectile function was measured as intracavernosal pressure (ICP) normalized to mean arterial pressure (MAP) following electrical stimulation of the cavernosal nerve. Venoocclusion was assessed by the maintenance of elevated in vivo ICP following intracorporal saline infusion. Vasoreactivity of isolated cavernosum in response to contractile and dilatory stimulation was examined in vitro by myography. Collagen and elastin content were evaluated by quantification of hydroxyproline and desmosine, respectively, as well as by quantitative PCR and histological analysis of isolated cavernosum. Erectile function was significantly decreased in db/db vs. BKS mice in a manner consistent with impairments in venoocclusive ability and decreased inflow. Heightened vasoconstriction and attenuated dilation in cavernosum of db/db vs. BKS mice suggest an overall lowered relaxation ability and thus impaired filling of the cavernosal spaces. A decrease in desmosine and hydroxyproline as well as lowered mRNA levels for tropoelastin, fibrillin-1, and alpha1(I) collagen were detected. These vasoreactive and sinusoidal matrix alterations may alter tissue compliance dispensability, preventing the normal expansion necessary for erection.     

Synthesis and evaluation of unsymmetrical bis(arylcarboxamides) designed as topoisomerase-targeted anticancer drugs.

Symmetrical dimers of lipophilic intercalating chromophores linked by cation-containing chains have recently been shown to have broad-spectrum in vivo anticancer activity. We report the preparation and evaluation of a series of both symmetric and unsymmetric dimers of a variety of intercalating chromophores of varied DNA binding strength, including naphthalimides, acridines, phenazines, oxanthrenes and 2-phenylquinolines. The unsymmetrical dimers were prepared by sequential coupling of the chromophores to linkers with selectively protected primary terminal amines to ensure high yields and unequivocal product. Protection of the internal (secondary) amines as BOC derivatives was used to ensure complete structural specificity, and was also an aid to the purification of these very polar compounds. The growth inhibitory abilities (as IC(50) values) of the compounds in a range of cell lines showed that the nature of the linker chain was important, and independent of the nature of the chromophore, with compounds containing the dicationic linker [-(CH2)2NH(CH2)2NH(CH2)2-] being on average 30-fold more potent than the corresponding compounds containing the monocationic linker [-(CH2)3NMe(CH2)3-]. However, the chromophores also play a role in determining biological activity, with the cytotoxicities of symmetric and unsymmetric dicationic dimers correlating with the overall DNA binding abilities of the chromophores.     

Toxicological evaluation of karaya gum; acute and subacute oral toxicity in rats

Male and female albino rats (Wistar strain) were given single and multiple doses of karaya gum suspended either in peanut oil or mixed with basal diet at different concentrations ranging from 0.5 to 8 g gum/kg body weight. The plant gum did not elicit any overt signs of toxicity or death in both sexes of rats. Daily administration of karaya gum mixed with basal diet at different dose levels (0, 5, 20 and 40 g gum/kg diet) for a period of 90 days showed no adverse effects in male and female rats. The body weight, growth pattern, food and water intake were comparable with those of the normal rats. There were no significant biochemical, or morphological alterations in the vital organs of experimental animals.