The proteolytic stability of 'designed' beta-peptides containing alpha-peptide-bond mimics and of mixed alpha,beta-peptides: application to the construction of MHC-binding peptides

Whereas alpha-peptides are rapidly degraded in vivo and in vitro by a multitude of peptidases, substrates constructed entirely of or incorporating homologated alpha-amino acid (i.e., beta-amino acid) units exhibit a superior stability profile. Efforts made so far to proteolytically hydrolyze a beta-beta peptide bond have not proved fruitful; a study aimed at breaching this proteolytic stability is discussed here. A series of such bonds have been designed with side-chain groups similar in relative positions (constitution) and three-dimensional arrangements (configuration) as found about alpha-peptidic amide bonds. Increasing the prospect for degradation would permit the tuning of beta-peptide stability; here, however, no cleavage was observed (1, 2, 4-6, Table 1). Peptides comprised of alpha- and beta-amino acids (mixed alpha,beta-peptides, 8-11) are expected to benefit from both recognition by a natural receptor and a high level of proteolytic stability, ideal characteristics of pharmacologically active compounds. Beta3-peptides containing alpha-amino acid moieties at the N-terminus are degraded, albeit slowly, by several peptidases. Of particular interest is the ability of pronase to cleave an alpha-beta peptide bond, namely that of alphaAla-beta3 hAla. Significantly, successful hydrolysis is independent of the configuration of the beta-amino acid. Some of the alpha,beta-peptides discussed here are being investigated for their binding affinities to class I MHC proteins. The computer-programming steps required to prepare alpha,beta-peptides on an automated peptide synthesizer are presented.     

All-trans-retinal is a closed-state inhibitor of rod cyclic nucleotide-gated ion channels

Rod vision begins when 11-cis-retinal absorbs a photon and isomerizes to all-trans-retinal (ATR) within the photopigment, rhodopsin. Photoactivated rhodopsin triggers an enzyme cascade that lowers the concentration of cGMP, thereby closing cyclic nucleotide-gated (CNG) ion channels. After isomerization, ATR dissociates from rhodopsin, and after a bright light, this release is expected to produce a large surge of ATR near the CNG channels. Using excised patches from Xenopus oocytes, we recently showed that ATR shuts down cloned rod CNG channels, and that this inhibition occurs in the nanomolar range (aqueous concentration) at near-physiological concentrations of cGMP. Here we further characterize the ATR effect and present mechanistic information. ATR was found to decrease the apparent cGMP affinity, as well as the maximum current at saturating cGMP. When ATR was applied to outside-out patches, inhibition was much slower and less effective than when it was applied to inside-out patches, suggesting that ATR requires access to the intracellular surface of the channel or membrane. The apparent ATR affinity and maximal inhibition of heteromeric (CNGA1/CNGB1) channels was similar to that of homomeric (CNGA1) channels. Single-channel and multichannel data suggest that channel inhibition by ATR is reversible. Inhibition by ATR was not voltage dependent, and the form of its dose-response relation suggested multiple ATR molecules interacting per channel. Modeling of the data obtained with cAMP and cGMP suggests that ATR acts by interfering with the allosteric opening transition of the channel and that it prefers closed, unliganded channels. It remains to be determined whether ATR acts directly on the channel protein or instead alters channel-bilayer interactions.     

Synthesis and biological activity of novel antibacterial quinazolines

Novel quinazolines, having interesting antibacterial activity have been prepared, characterized and tested against a panel of susceptible and resistant Gram positive and Gram negative organisms.     

Quinazolines revisited: search for novel anxiolytic and GABAergic agents

A systematic approach through computer assisted design to identify novel quinazolines having anxiolytic and GABAergic activity has been reported.     

Mutation analysis of hMSH2 and hMLH1 in colorectal cancer patients in India

The aim of this work was to study the mutation profile in hMSH2 and hMLH1 genes in hereditary nonpolyposis colorectal cancer (HNPCC) patients in India. On the basis of the Bethesda criteria, 31 colorectal cancer patients were studied first for microsatellite instability, using the five markers recommended by the Bethesda guidelines. Twelve of 31 tumor samples were found to be MSI-H, 9 of 31 were MSI-L, and the rest were MSS. The 12 patients with MSI-H were analyzed for mutations in hMSH2 and hMLH1 genes using PCR-denaturing high-performance liquid chromatography (dHPLC), followed by sequencing of samples showing abnormal peaks. Of the five mutations detected, three were found to be deleterious mutations (hMSH2-R680X, hMLH1-E671X, and a splice junction mutation IVS16-2A --> G); one had a mutation of probable significance (hMLH1-C680G) and one was of unknown significance (hMSH2-R171K). This study has also shown that most of the early-onset colon (4/7) and early-onset rectal (15/21) cancers are MSS or MSI-L. This is the first study to describe the mutation in hMSH2 and hMLH1 in Indian patients, a low incidence region for colorectal cancer. A two-stage procedure using MSI testing followed by PCR-dHPLC was found to be an efficient method in studying the mutation profile in high-risk patients.     

Grape seed extract proanthocyanidins downregulate HIV-1 entry coreceptors,CCR2b,CCR3 and CCR5 gene expression by normal peripheral blood mononuclear cells

Flavonoids and related polyphenols, in addition to their cardioprotective, anti-tumor, anti-inflammatory, anti-carcinogenic and anti-allergic activities, also possess promising anti-HIV effects. Recent studies documented that the beta-chemokine receptors, CCR2b, CCR3 and CCR5, and the alpha-chemokine receptors, CXCR1, CXCR2 and CXCR4 serve as entry coreceptors for HIV-1. Although flavonoids and polyphenolic compounds elicit anti-HIV effects such as inhibition of HIV-1 expression and virus replication, the molecular mechanisms underlying these effects remain to be clearly elucidated. We hypothesize that flavonoids exert their anti-HIV effects, possibly by interfering at the HIV co-receptor level. We investigated the effect of flavonoid constituents of a proprietary grape seed extract (GSE) on the expression of HIV-1 coentry receptors by immunocompetent mononuclear leukocytes. Our results showed that GSE significantly downregulated the expression of the HIV-1 entry co-receptors, CCR2b, CCR3 and CCR5 in normal PBMC in a dose dependent manner. Further, GSE treated cultures showed significantly lower number of CCR3 positive cells as quantitated by flow cytometry analysis which supports RT-PCR gene expression data. Investigations of the mechanisms underlying the anti-HIV-1 effects of grape seed extracts may help to identify promising natural products useful in the prevention and/or amelioration of HIV-1 infection.     

The flavonoid,quercetin, differentially regulates Th-1 (IFNgamma) and Th-2 (IL4) cytokine gene expression by normal peripheral blood mononuclear cells

Flavonoids are plant metabolites that are dietary antioxidants and exert significant anti-tumor, anti-allergic, anti-inflammatory and anti-viral effects. It is generally accepted that Th-1 derived cytokines such as IL-2, IFNgamma and IL-12 promote cellular immunity while Th-2 derived cytokines such as IL-4, IL-5, IL-6 exert negative immunoregulatory effects on cellular immunity while upregulating humoral immunity. The molecular mechanisms underlying the biological activities of flavonoids have not been elucidated. We hypothesize that the flavonoid, quercetin, exert significant anti-viral and anti-tumor effects possibly by modulating the production of Th-1 and Th-2 derived cytokines. Peripheral blood mononuclear cells (PBMC, 1 x 10(6) cells/ml) from normal subjects were cultured with different concentrations of quercetin (0.5-50 microM) for 24-72 h and supernates were quantitated for IFN-gamma and IL-4 by ELISA and antiviral activity of IFNgamma by bioassay. FACS analysis was done to determine the number of IFN-gamma and IL-4 positive cells and RT-PCR was done to quantitate gene expression. Quercetin significantly induces the gene expression as well as the production of Th-1 derived IFNgamma and the downregulates Th-2 derived IL-4 by normal PBMC. Further, quercetin treatment increased the phenotypic expression of IFNgamma cells and decreased IL-4 positive cells by FACS analysis, which corroborate with protein secretion and gene expression studies. These results suggest that the beneficial immuno-stimulatory effects of quercetin may be mediated through the induction of Th-1 derived cytokine, IFNgamma, and inhibition of Th-2 derived cytokine, IL-4.     

Glyceroneogenesis and the source of glycerol for hepatic triacylglycerol synthesis in humans

Glyceroneogenesis, i.e. the synthesis of the glycerol moiety of triacylglycerol from pyruvate, has been suggested to be quantitatively important in both the liver and adipose tissue during fasting. However, the actual contribution of glyceroneogenesis to triacylglycerol synthesis has not been quantified in vivo in human studies. In the present study we have measured the contribution of glycerol and pyruvate to in vivo synthesis of hepatic triacylglycerol in nonpregnant and pregnant women after an overnight fast. Five nonpregnant women were administered [(13)C(3)]glycerol tracer as prime constant rate infusion, and the appearance of tracer in plasma glucose and triacylglycerol was quantified using gas chromatography-mass spectrometry. The contribution of pyruvate to hepatic triacylglycerol was quantified in nonpregnant and pregnant women using the deuterium labeling of body water method. The appearance of [(2)H] in hydrogens on C(1) and C(3) of triacylglycerol was measured following periodate oxidation of the glycerol isolated from hydrolyzed triacylglycerol. After a 16-h fast, approximately 6.1% of the plasma triacylglycerol pool was derived from plasma glycerol, whereas 10 to 60% was derived from pyruvate in nonpregnant women and pregnant women early in gestation. Our data suggest that glyceroneogenesis from pyruvate is quantitatively a major contributor to plasma triacylglycerol synthesis and may be important for the regulation of very low density lipoprotein triacylglycerol production. Our data also suggest that 3-glycerol phosphate is in rapid equilibrium with the triosephosphate pool, resulting in rapid labeling of the triose pool by the administered tracer glycerol. Because the rate of flux of triosephosphate to glucose during fasting far exceeds that to triacylglycerol, more glycerol ends up in glucose than in triacylglycerol. Alternatively, there may be two distinct pools of 3-glycerol phosphate in the liver, one involved in generating triosephosphate from glycerol and the other involved in glyceride-glycerol synthesis.     

Short Note: Biodegradation of chlorobenzoates by Actinomycetes

Of the nine actinomycete strains screened for their ability to grow on isomeric chlorobenzoates (Cba), Corynebacterium liquefaciens, a sewage isolate, was able to maximally metabolize 3.2mM 2- and 3-Cba in presence of 0.25mM glucose as co-substrate. The degradation of 2-Cba and 3-Cba was 70.3% and 79.37% (w/v), respectively, under optimized conditions.