Effects of C-terminal amidation and heptapeptide ring on the biological activities and advanced structure of amurin-9KY, a novel antimicrobial peptide identified from the brown frog, Rana kunyuensis

Rana kunyuensis is a species of brown frog that lives exclusively on Kunyu Mountain,Yantai,China.In the current study,a 279-bp cDNA sequence encoding a novel antimicrobial peptide (AMP),designated as amurin-9KY,was cloned from synthesized double-strand skin cDNA of R.kunyuensis.The amurin-9KY precursor was composed of 62 amino acid (aa) residues,whereas the mature peptide was composed of 14 aa and contained two cysteines forming a C-terminal heptapeptide ring (Rana box domain) and an amidated C-terminus.These structural characters represent a novel amphibian AMP family.Although amurin-9KY exhibited high similarity to the already identified amurin-9AM from R.amurensis,little is known about the structures and activities of amurin-9 family AMPs so far.Therefore,amurin-9KY and its three derivatives (amurin-9KY1-3) were designed and synthesized.The structures and activities were examined to evaluate the influence of C-terminal amidation and the heptapeptide ring on the activities and structure of amurin-9KY..Results indicated that C-terminal amidation was essential for antimicrobial activity,whereas both C-terminal amidation and the heptapeptide ring played roles in the low hemolytic activity.Circular dichroism (CD) spectra showed that the four peptides adopted an α-helical conformation in THF/H2O (v/v 1∶1) solution,but a random coil in aqueous solution.Elimination of the C-terminal heptapeptide ring generated two free cysteine residues with unpaired thiol groups,which greatly increased the concentration-dependent anti-oxidant activity.Scanning electron microscopy (SEM) was also performed to determine the possible bactericidal mechanisms.

Optimization of Adsorption Conditions of Papain on Cross-Linked Phage-Displayed Heptapeptide Matrix Using Response Surface Methodology

A new cross-linked heptapeptide matrix(CHM)was prepared and the adsorption performance for papain was investigated.Firstly,a phage-displayed heptapeptide(Ile-Gln-SerPro-His-Phe-Phe)with high affinity to papain was found.Secondly,the heptapeptide was cross-linked to a matrix for papain adsorption.Finally,the adsorption conditions were optimized by response surface methodology.The results indicated that the optimum adsorptionconditionsweredeterminedasinitialpH 6.9,temperature 40℃,and the adsorption capacity of CHM for papain was found to be 55.52 mg/g.Moreover,the papain was purified 78-fold in a single step determined by affinity precipitation.More than87%of the adsorbed papain was desorbed using the eluent solventtriethylamine at pH 7.4.The results show that the CHM is a promising adsorbent for papain purification from crude papaya powder.

Studies on Synthesis of a Cycloheptapeptide and Effects of Different Metal Ions on the Cyclization

A cyclic heptapeptide, c(Gly-Ile-Pro-Tyr-Ile-Ala-Ala), which was isolated and identified from Stellaria yumumensis French (M), was synthesized by solution method for the first time. Protected heptapeptide Z-Gly-Ile-Pro-Tyr-Ile-Ala-Ala-OBzl was synthesized with 3-(diethoxy-phosphoryloxy)-l,2,3-benzotriazin-4(3H)-one (DEPBT) as a coupling reagent. After deprotection of benzyl and benzyloxycarbonyl groups, a free linear heptapeptide H-Gly-Ile-Pro-Tyr-Ile-Ala-Ala-OH was cyclized in DMF (2 × 10?3 mol/L) in the presence of nine different metal ions, i. e., Li+, Na+, K+, Cs+, Mg2+, Ca2+, Bai2+, Nr2+ and Cr5+ respectively, using DEPBT as a coupling reagent. Univalent metal ion Cs+ enhanced both the cyclization yield and cyclization rate of H-Gly-De-Pro-Tyr-Ile-Ala-AlaOH, while some bivalent metal ions, such as Mg2+, Ca2+ and Ni2+ decreased the yields of c (Gly-Ile-Pro-Tyr-De-Ala-Ala) drastically. Trivalent metal ion Cr3+ even inhibited the cyclization reaction completely.

One-pot in-situ synthesis of coralloid supported VO_(2)catalyst for intensified aerobic oxidative desulfurization

A coralloid 3D g-C_(3)N_(4)supported VO_(2)catalyst was successfully synthesized in-situ by one-pot method,avoiding the agglomeration of VO_(2)during the reaction.The morphological and compositional information of the supported catalyst were investigated detailedly.30%VO_(2)/3D g-C_(3)N_(4)revealed excellent catalytic activity in aerobic oxidative desulfurization,the oxidative of dibenzothiophene(DBT),4-methyldibenzothiophene(4-MDBT)and 4,6-dimethyldibenzothiophene(4,6-DMDBT)reached 98.6%,99%and 99.4%,respectively,under the same mild conditions.The recycling performance and the mechanism on the oxidative of DBT were studied as well.

Chiral LVFFARK enantioselectively inhibits amyloid-β protein fibrillogenesis

The modulation of protein aggregation is involved not only in biochemical engineering processes,but also in in vivo biological events such as Alzheimer's disease(AD)that features amyloid-βprotein(Aβ)deposits.Inspired by the different pharmacological efficacy of enantiomers,taking heptapeptide LVFFARK(LK7)as an example,herein the chiral influence of peptide inhibitors on Aβfibrillogenesis and cytotoxicity was investigated by extensive biophysical and biological analyses.It was intriguing to find that although both LLK7 and D-LK7 could inhibit Aβaggregation in a concentration-dependent manner,it was the D-enan-tiomer that exhibited chirality preference and selectivity for modulation of Aβself-assembly.As com-pared with L-LK7 at the same conditions,D-LK7 showed significantly enhanced potency on suppressing cross-βsheet formation,fibrillar Aβaggregates deposition,Aβconformational transition,and Aβ-triggered neurotoxicity on cultured cells.For instance,L.LK7 and D-LK7 rescued cells by increasing cell via-bility from 60%to 62%and 84%at 100μmolL^(-1),respectively.The chiral discrimination of L-LK7 and D-LK7 was further validated by the different elimination efficiency on amyloid accumulation in AD model nematodes.It is considered that the higher binding affinity of D-LK7 to Aβmonomers than that of L LK7 resulted in the stronger inhibition effect.This work provided new insights into understanding chiral-ity in the interaction with Aβand the consequent inhibitory effect,and would contribute to the design of anti-amyloid agents.