A library of linear undecapeptides with bactericidal activity against phytopathogenic bacteria

A 125-member library of synthetic linear undecapeptides was prepared based on a previously described peptide H-K¹KLFKKILKF¹⁰L-NH₂ (BP76) that inhibited in vitro growth of the plant pathogenic bacteria Erwinia amylovora, Xanthomonas axonopodis pv. vesicatoria, and Pseudomonas syringae pv. syringae at low micromolar concentrations. Peptides were designed using a combinatorial chemistry approach by incorporating amino acids possessing various degrees of hydrophobicity and hydrophilicity at positions 1 and 10 and by varying the N-terminus. Library screening for in vitro growth inhibition identified 27, 40 and 113 sequences with MIC values below 7.5 μM against E. amylovora, P. syringae and X. axonopodis, respectively. Cytotoxicity, bactericidal activity and stability towards protease degradation of the most active peptides were also determined. Seven peptides with a good balance between antibacterial and hemolytic activities were identified. Several analogues displayed a bactericidal effect and low susceptibility to protease degradation. The most promising peptides were tested in vivo by evaluating their preventive effect of inhibition of E. amylovora infection in detached apple and pear flowers. The peptide H-KKLFKKILKYL-NH₂ (BP100) showed efficacies in flowers of 63–76% at 100 μM, being more potent than BP76 and only less effective than streptomycin, currently used for fire blight control.     

The analogs of oxytocin and D-homoarginine vasopressin with bulky substituted phenylalanine in position 2

Solid phase technique on p-methylbenzhydrylamine resin wasused for the synthesis of eight analogs of oxytocin and 8-D-homoarginine vasopressin with the non-coded amino acids L- or D-2,3,4,5,6-pentamethylphenylalanine and L- or D-4-phenylphenylalanine in position 2. The preparation of theabove mentioned non-coded amino acids is described as well.All eight analogs were found to be potent inhibitors ofoxytocin activity in the uterotonic in vitro test in theabsence of Mg²⁺ ions. In the uterotonic test invitro in the presence of Mg²⁺ and in the test invivo, their potency is strongly decreased or completelyabolished. The substances are also weak pressor inhibitors.The L or D configuration does not seem to influence theactivity significantly.     

Formation mechanism of cross‐linking Maillard compounds in peptide–xylose systems

The formation mechanism of Maillard peptides was explored in Maillard reaction through diglycine/glutathione(GSH)/(Cys‐Glu‐Lys‐His‐Ile‐Met)–xlyose systems by heating at 120 °C for 30–120 min. Maximum fluorescence intensity of Maillard reaction products (MRPs) with an emission wavelength of 420~430 nm in all systems was observed, and the intensity values were proportional to the heating time. Taken diglycine/GSH–[¹³C₅]xylose systems as a control, it was proposed that the compounds with high m/z values of 379 and 616 have the high molecular weight (HMW) products formed by cross‐linking of peptides and sugar. In (Cys‐Glu‐Lys‐His‐Ile‐Met)–xylose system, the m/z value of HMW MRPs was not observed, which might be due to the weak signals of these products. According to the results of gel permeation chromatography, HMW MRPs were formed by Maillard reaction, especially in (Cys‐Glu‐Lys‐His‐Ile‐Met)–xylose system, the percentage of Maillard peptides reached 52.90%. It was concluded that Maillard peptides can be prepared through the cross‐linking of sugar and small peptides with a certain MW range. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

New metabolites of Azotobacter vinelandii exhibiting antifungal activity

New metabolites exhibiting antifungal activity were isolated from the culture liquid of Azotobacter vinelandii strain IB 4. The metabolites were characterized by IR and ¹³C-NMR spectroscopy and defined as sucrose polythiophosphates of tetraamine (α-D-2,3-diaminoglucopyranosyl-β-D-3,4-diaminofructofuranose).     

Comparison of peptidase activities in some fungi pathogenic to arthropods

Peptidases, highly specific toward several synthetic chromogenic peptides, were found in the mycelia of four arthropod pathogenic fungi: Aphanomyces astaci, Beauveria bassiana, Metarrhizium anisopliae, and Paecilomyces farinosus. A. astaci peptidases had high hydrolyzing activities toward most of the peptides, especially those with arginine in the P1 position, while those of B. bassiana and P. farinosus readily hydrolyzed peptides with valine and arginine, as well as proline and tyrosine in the P2 and P1 positions, respectively. The hydrolyzing capacities of M. anisopliae peptidases were similar to A. astaci, but showed lower specific activities. Casein or azocoll was only hydrolyzed by A. astaci peptidases. B. bassiana and M. anisopliae had a very low hydrolyzing capacity toward casein and could not degrade azocoll. P. farinosus had no hydrolyzing activity toward casein or azocoll. Only peptidases from the crayfish pathogen A. astaci could degrade the crayfish cuticle. The peptidase preparations of A. astaci and B. bassiana hydrolyzing MeO-Suc-Arg-Pro-Tyr-pNA or Bz-Phe-Val-Arg-pNA were of the serine type. The possible importance of peptidase activity of arthropod pathogenic fungi in the infection process is discussed.     

An intramolecular linkage involving isodityrosine in extensin

We isolated isodityrosine, a diphenyl ether linked amino acid, from cell wall hydrolysates and from two tryptic peptides of extensin. Determination of the molecular weights, net charges and composition of the peptides indicated that isodityrosine (IDT) can form a short intramolecular linkage in sequences consisting of:

     

穿膜肽的内化机制及其应用

穿膜肽是一类具有特殊穿膜功能的多肽分子,能携带其它分子甚至超分子颗粒穿膜进入细胞内部．早期研究认为,其进胞是一种无需受体、也不存在饱和状态的非经典胞吞行为．近年研究表明,其穿膜机制可能与其含有的氨基酸种类有很大关系．现在,穿膜肽的穿膜过程称为巨型胞饮行为,它与传统的胞吞形式很相似．当然,还可能存在着其它的进胞方式而没有被证明或发现．关于穿膜肽的应用也是人们最感兴趣的,在很多领域的研究都在进行并不断取得进展．不论是生物界还是医学界,穿膜肽都被认为将是一类非常有发展潜力的多肽分子．     

Direct comparison of the pharmacodynamics of four antifungal drugs in a mouse model of disseminated candidiasis using microbiological assays of serum drug concentrations

The aim of this study was to compare the pharmacodynamics of the azole antifungal drugs fluconazole, itraconazole and ketoconazole, and the polyene antifungal amphotericin B, in a mouse model of disseminated Candida albicans infection. In order to directly compare effective serum concentrations of these antifungals, drug concentrations were assayed microbiologically by measuring inhibition of C. albicans mycelial growth (mMIC) in a mouse serum-based assay (serum antifungal titer). Efficacy in the mouse infection model was determined using an organ-based (kidney burden) endpoint. For all four drugs, the serum antifungal titers, 8 hr after administration of single doses of drugs at a range of drug concentrations, correlated closely with C. albicans kidney fungal burden in the mouse model. The results showed that determining serum antifungal titer may be used to accurately represent kidney fungal burden in a mouse model of disseminated candidiasis and allowed direct comparison of the pharmacodynamics of differing classes of antifungal drugs.     

Factors governing 3(10)-helix vs alpha-helix formation in peptides: percentage of C(alpha)-tetrasubstituted alpha-amino acid residues and sequence dependence

As an additional step toward the dissection of the factors responsible for the onset of 3(10)-helix vs alpha-helix in peptides, in this paper we describe the results of a three-dimensional (3D) structural analysis by x-ray diffraction of the N(alpha)-acylated heptapeptide alkylamide mBrBz-L-Iva-L-(alphaMe)Val-L-Abu-L-(alphaMe)Val-L-(alphaMe)Phe-L-(alphaMe)Val-L-Iva-NHMe characterized by a single (L-Abu3) C(alpha)-trisubstituted and six C(alpha)-tetrasubstituted alpha-amino acids. We find that in the crystal state this peptide is folded in a mixed helical structure with short elements of 3(10)-helix at either terminus and a central region of alpha-helix. This finding, taken together with the published NMR and x-ray diffraction data on the all C(alpha)-methylated parent sequence and its L-Val2 analog (also the latter heptapeptide has a single C(alpha)-trisubstituted alpha-amino acid) strongly supports the view that one C(alpha)-trisubstituted alpha-amino acid inserted near the N-terminus of an N(alpha)-acylated heptapeptide alkylamide sequence may be enough to switch a regular 3(10)-helix into an essentially alpha-helical conformation. As a corollary of this work, the x-ray diffraction structure of the N(alpha)-protected, C-terminal tetrapeptide alkylamide Z-L-(alphaMe)Val-L-(alphaMe)Phe-L-(alphaMe)Val-L-Iva-NHMe, also reported here, is clearly indicative of the preference of this fully C(alpha)-methylated, short peptide for the 3(10)-helix. As the same terminally blocked sequence is mixed 3(10)/alpha-helical in the L-Abu3 heptapeptide amide but regular 3(10)-helical in the tetrapeptide amide and in the parent heptapeptide amide, these results point to an evident plasticity even of a fully C(alpha)-methylated short peptide.     

Amyloid‐like aggregation of designer bolaamphiphilic peptides: Effect of hydrophobic section and hydrophilic heads

Amyloid‐like aggregation of natural proteins or polypeptides is an important process involved in many human diseases as well as some normal biological functions. Plenty of works have been done on this ubiquitous phenomenon, but the molecular mechanism of amyloid‐like aggregation has not been fully understood yet. In this study, we showed that a series of designer bolaamphiphilic peptides could undergo amyloid‐like aggregation even though they didn't possess typical β‐sheet secondary structure. Through systematic amino acid substitution, we found that for the self‐assembling ability, the number and species of amino acid in hydrophobic section could be variable as long as enough hydrophobic interaction is provided, while different polar amino acids as the hydrophilic heads could change the self‐assembling nanostructures with their aggregating behaviors affected by pH value change. Based on these results, novel self‐assembling models and aggregating mechanisms were proposed, which might provide new insight into the molecular basis of amyloid‐like aggregation.