Heterologous expression of the novel dimeric antimicrobial peptide LIG in Pichia pastoris

The antimicrobial peptide (AMP) LI is a fusion product of antimicrobial peptide LL37 produced by human neutrophils and Indolicidin secreted by bovine neutrophils. LI retained the antimicrobial activity of the parental peptides and showed high cell selectivity. In this study, the flexible linker Gly-Ser-Gly (G-S-G) was used to ligate LI into dimeric LIG, and constructed the Pichia pastoris (P. pastoris) expression vector pPIC9K-6×His-3×FLAG-LIG. The total protein expression of P. pastoris GS115 reached the highest level (189.6 mg/L) after 96 h induction with 3 % methanol at the initial pH value of 7.0. Finally, 5.9 mg/L of recombinant LIG (rLIG) was obtained after enterokinase digestion and purification. The rLIG had high antimicrobial activity and low hemolytic activity. Compared with monomer LI, GSG linked dimeric LIG, which had no significant change in antimicrobial activity and had good salt ions stability. In this study, the dimeric antimicrobial peptide LIG was successfully expressed, which provided a new idea for the expression of AMPs in the P. pastoris expression system, and had important significance for the application of AMPs.

Design and heterologous expression of a novel dimeric LL37 variant in Pichia pastoris

BACKGROUND

The antimicrobial peptide LL37 is produced by white blood cells (mainly neutrophils) and various epithelial cells, and has the outstanding advantages of participating in immune regulation, causing chemotaxis of immune cells and promoting wound healing. However, the central domain of LL37 needs to be improved in terms of antimicrobial activity.

RESULTS

In this study, the amino acid substitution method was used to improve the antimicrobial activity of the LL37 active center, and a dimeric design with a better selection index was selected. A flexible linker was selected and combined with the 6 × His-SUMO tag and LG was successfully expressed using Pichia pastoris as a host. Recombinant LG displayed strong antimicrobial activity by destroying the cell membrane of bacteria but had low hemolytic activity. In addition, compared with monomeric peptide FR, rLG had improved ability to tolerate salt ions.

CONCLUSION

This research provides new ideas for the production of modified AMPs in microbial systems and their application in industrial production.

Antinociceptive grayanane-derived diterpenoids from flowers of Rhododendron molle

Twelve new grayanoids (1-12) along with five known compounds were isolated from flowers of Rhododendron molle. Their structures were fully characterized using a combination of spectroscopic analyses, computational calculations, and single crystal X-ray diffraction. Rhomollone A (1) possesses an unprecedented 5/6/6/5 tetra-cyclic ring system (B-nor grayanane) incorporating a cyclopentene-1,3-dione scaffold. Rhodomollein XLIII (2) is a dimeric grayanoid, containing a novel 14-membered heterocyclic ring with a C ₂ symmetry axis. The antinociceptive activities of compounds 3, 4, 6, 7, and 12-17 were evaluated by an acetic acid-induced writhing test. Among them, compounds 3, 7, 12, 15 and 16 displayed significant antinociceptive activities at a dose of 20 mg/kg with inhibition rates ranging from 41.9% to 91.6%. Compounds 6 and 13 inhibited 46.0% and 39.4% of the acetic acid-induced writhes at a dose of 2 mg/kg, while compound 17 inhibited 34.3% of the writhes at a dose of 0.4 mg/kg.

Neriifolin S, a dimeric serine protease from Euphorbia neriifolia Linn.: Purification and biochemical characterisation

A dimeric serine protease Neriifolin S of molecular mass 94kDa with milk clotting activity has been purified from the latex of Euphorbia neriifolia by anion exchange and size-exclusion chromatography. It hydrolyses peptidyl substrates l-Ala-pNA with highest affinity (K_m of 0.195mM) and physiological efficiency (K_cat/K_m of 144.5mMs). Enzyme belongs to the class of neutral proteases with pI value of 6.8, optimal proteolytic activity displayed at pH 9.5 and temperature 45°C. Its proteolytic activity is strongly stimulated in the presence of Ca⁺² ions and exclusively inhibited by serine protease inhibitors. Enzyme is fairly stable toward chemical denaturants, pH and temperature. The apparent T_m, was found to be 65°C. Thermal inactivation follow first order kinetics with activation energy (Ea), activation enthalpy (ΔH∗), free energy change (ΔG∗) and entropy (ΔS∗) of 27.54kJmol^-1, 24.89kJmol^-1, -82.34kJmol^-1 and 337.20Jmol^-1K^-1.