Biomedical peptides, proteins & nucleic acids : structure, synthesis & biological activity最新文献

A low dead-volume, 40 nmole scale column was designed for automated, solid-support oligonucleotide synthesis. The LV40 columns are filled with 1000A, high-cross link polystyrene beads at the 40 nmole scale. Reducing the unoccupied volume and optimizing the column dimensions allows efficient and fast synthesis on existing commercial synthesizers with low reagent consumption. Three spectrally distinct fluorescent dyes were applied as phosphoramidites in the synthesis of PCR primers. Fluorescent labelled PCR products of the Mfd11 microsatellite locus were analyzed.

A pool of five oligonucleotides has been used to detect the pathogenic organism Mycobacterium avium subspecies paratuberculosis in PCR-amplified DNA from ruminants. The oligonucleotides were labelled at the 5'-end with three dinitrophenyl reporter groups and hybridised to the target DNA, which was fixed to a nylon membrane by ultraviolet irradiation. Colourimetric detection of the PCR product was carried out using an anti-DNP antibody conjugated to horseradish peroxidase or to alkaline phosphatase. Detection with alkaline phosphatase was more sensitive than with horseradish peroxidase but, in both cases, the PCR product could be easily detected. The DNP labelling system offers an economic and effective alternative to biotin, digoxigenin or fluorescein for the detection of PCR-amplified DNA.

Oral administration of the tetrapeptide Asn-Leu-Pro-Arg (NLPR) to memory-impaired rats results in improved acquisition and maintenance of behavioural response and also facilitates nerve growth factor (NGF) expression in the brain. It is suggested that NLPR can ameliorate memory disability by promoting NGF gene expression, so implying that NLPR is a potential drug candidate for curing memory impairment.

Human lung surfactant peptide SP-C and two of its N-terminal fragments were prepared by SPPS and their biophysical activities investigated in vitro using a pulsating bubble surfactometer. These studies demonstrated that even low doses of the synthetic peptides with the natural human sequence of SP-C in combination with reconstituted lipid mixtures causes a drastic decrease of surface tension.

With the aim of synthesizing cyclic antagonists of the nonapeptide hormone bradykinin with minimal side chain modification, we performed backbone to backbone and backbone to side chain cyclization. To probe and compare different strategies for this new kind of cyclization, the branched peptide bonds were formed by both reductive alkylation on the solid phase and by using preformed building units. Lactam bridges between the modified amide groups were formed by the use of the phenylalanine derivatives N(CH2COOH)Phe and N(CH2CH2NH2)Phe. The best results in the formation of the N-alkylamide bond were obtained with the coupling reagent PyBrop. The coupling rate was monitored by estimation of the N-terminal Fmoc-group. The cyclization was performed on the solid support. Unexpected difficulties resulted from the instability of the N-alkylamide bond under strong acidic conditions, as used for deprotection and for removal from the resin. We synthesized peptides with backbone to backbone cyclization between positions 2 and 5, as well as backbone to side chain cyclizations between positions 0 and 5, and between 2 and 6. The relatively high biological activities of some of the cyclic analogues support the supposed receptor-bound conformation of bradykinin antagonists with a beta-turn in the N-terminal sequence.

Pituitary adenylate cyclase activating polypeptide (PACAP) specific radioimmunoassay systems have been developed and the distribution of PACAPs in guinea pig tissues has been studied. The antibody against PACAP38 was characterized, using synthetic peptide fragments. It was shown to recognize the C-terminal portion with the C-terminal amide group and no cross-reaction was observed with vasoactive intestinal polypeptide (VIP), which has a high homology with PACAP27 and the N-terminal 28 amino acid residues of PACAP38. The antibody against PACAP27 was specific to PACAP27. With the two PACAPs (PACAP38 and PACAP27) specific RIA systems, high concentrations of PACAP38- and PACAP27-like immunoreactivity (LI) were observed in the brain of guinea pigs, especially in the diencephalon (mostly hypothalamus). In all tissues PACAP38-LI was higher than that of PACAP27-LI. Reverse-phase HPLC showed that PACAP38- and PACAP27-LI of tissue extracts were superimposed at the elution position of those of the synthetic peptides, respectively.

The affinity of interaction between two monoclonal antibodies and a synthetic peptide representing the C-terminal 23 residues of the heavy chain (HA1) of influenza virus hemagglutinin were determined using an air-driven ultracentrifuge. The technique makes use of common laboratory equipment and is based on sound theoretical principles. Because the method does not rely on the solid-phase immobilisation of one of the interacting species, it circumvents problems associated with ELISA-like assays, which, in the case of peptides, may involve the immobilisation of ligand through association of amino acid residues necessary for recognition by antibody. The technique should be applicable to the study of a wide range of ligand-acceptor systems. Because only one of the reagents needs to be pure to allow labelling, prior purification of the biological receptor is not necessary. The method also lends itself to inhibition experiments in which the effects of various homologs on the binding event can be examined in a way which permits an evaluation of potential agonists and antagonists.

Recently, the sequence of mitochondrial chaperonin 10 from Rattus norvegicus (rat cpn10), with N-terminal acetylation, has been published. Two syntheses of rat cpn10 were performed, the first using a classical carbodiimide-mediated double coupling protocol (Method A) and the second a more efficient HBTU/HOBT/single coupling procedure (Method B). The latter also involved the application of a capping procedure, using N-(2-chlorobenzyloxycarbonyloxy)succinimide [Z(2-Cl)-OSu]. The crude protein from Method A was purified using a two-step isoelectric focusing/RP-HPLC scheme and found to contain a high proportion of a deletion peptide (less Gln60). Conversely, rat cpn10 from Method B was purified to homogeneity by one-step RP-HPLC, using a reversible lipophilic chromatographic probe. The proportion of biologically active heptameric structure was directly related to the purity of the protein and attained 84% with material from Method B. The addition of Ca/Mg ions, pH 7.2, or a heating/cooling cycle increased the proportion of heptamer for less pure protein. Shorter sequences were found not to fold into heptamers, suggesting that aggregation/folding motifs are located in 1-25 and 77-101 regions of rat cpn10. The heptameric cpn10 (Method B) bound correctly to GroEL from E. coli, demonstrating that N-terminal acetylation is not necessary for its folding and binding to bacterial cpn60.

Analogues of beta-amyloid (32-42) peptide, containing N-(2-hydroxy-4-methoxybenzyl) (Hmb) amide backbone substitutions at various positions have been prepared using fluoren-9-ylmethoxycarbonyl (Fmoc)-polyamide based solid phase peptide synthesis. On-line N alpha-Fmoc deprotection monitoring during assembly exhibited hindered release in the native and beta A(34-42, (Hmb)Gly38) analogue syntheses. No such hindrance was observed during the synthesis of beta A(34-42, (Hmb)Gly37) nor beta A(34-42, (Hmb)Val36). However, the latter contained an exceptionally slow coupling reaction. Cleaved peptides were analysed for solubility in a variety of solvents and insoluble pellets tested for congophilic staining. X-ray analysis of Fmoc (and H-) beta A(34-42) and the corresponding (Hmb)Gly38 analogues as dimethylformamide swollen gels gave very similar structures. Secondary structure prediction and model-building of ordered arrays, compatible with our results, suggest that beta A(34-42) forms a beta-hairpin structure, with the reverse turn at Val36-Gly37-Gly38-Val39 both in solution and on the resin during synthesis.

The high affinity receptor for IgE, Fc epsilon RI, is responsible for immediate hypersensitivity reactions. In rodents Fc epsilon RI is a tetrameric complex, alpha beta gamma 2 of non-covalently attached subunits: one IgE-binding alpha subunit with the binding site in the extracellular part of the chain, one beta-subunit and a dimer of disulphide linked gamma-subunits. Although there is an increasing evidence that the gamma-subunit chains are important signalling proteins that appear to function through a common Tyr-Leu-Tyr-Leu amino acid motif present in their cytoplasmic tails, which link the ligand binding specificity of their associated chains to signal transduction pathways, many questions related to conformation and function of this subunit remain to be answered. In the present work, the 36-residue cytoplasmic domain of the gamma-subunit has been synthesized and conformational studies by the combined use of Fourier transform infrared (FTIR), circular dichroism (CD) and nuclear magnetic resonance (NMR) have been performed. Based on the constraints found by these methods, conformational models of the cytoplasmic tail of the gamma-subunit are proposed and discussed.