Antimicrobial nano-assemblies of tryptocidine C, a tryptophan-rich cyclic decapeptide, from ethanolic solutions

Tryptocidine C (TpcC), a Trp-rich cyclodecapeptide is a minor constituent in the antibiotic tyrothricin complex from Brevibacillus parabrevis. TpcC possesses a high tendency to oligomerise in aqueous solu-tions and dried TpcC forms distinct self-assembled nanoparticles. High-resolution scanning electron microscopy revealed the influence of different ethanol:water solvent systems on TpcC self-assembly, with the TpcC, dried from a high concentration in 15% ethanol, primarily assembling into small nano -spheres with 24.3 nm diameter and 0.05 polydispersity. TpcC at 16 mM, near its CMC, formed a variety of structures such as small nanospheres, large dense nanospheroids and facetted 3-D-crystals, as well as sheets and coarse carpet-like structures which depended on ethanol concentration. Drying 16 mM TpcC from 75% ethanol resulted in highly facetted 3-D crystals, as well as small nanospheres, while those in 10% ethanol preparation had less defined facets. Drying from 20 to 50% ethanol led to polymorphic ar-chitectures with a few defined nanospheroids and various small nanoparticles, imbedded in carpet-and sheet-like structures. These polymorphic surface morphologies correlated with maintenance of fluo-rescence properties and the surface-derived antibacterial activity against Staphylococcus aureus over time, while there was a significant change in fluorescence and loss in activity in the 10% and 75% preparations where 3-D crystals were observed. This indicated that TpcC oligomerisation in solutions with 20-50% ethanol leads to metastable structures with a high propensity for release of antimicrobial moieties, while those leading to crystallisation limit active moieties release. TpcC nano-assemblies can find application in antimicrobial coatings, surface disinfectants, food packaging and wound healing materials.(c) 2022 Elsevier B.V. and Societe Francaise de Biochimie et Biologie Moleculaire (SFBBM). All rights reserved.

Automated summary

TpcC, a Trp-rich cyclodecapeptide, can oligomerize and form self-assembled nanoparticles in aqueous solutions. The solvent system of ethanol:water has an influence on TpcC self-assembly, with different structures observed based on ethanol concentration. The drying process from 20 to 50% ethanol resulted in polymorphic surface morphologies with various small nanoparticles, while drying from 75% ethanol led to highly facetted 3-D crystals. The TpcC nano-assemblies have potential applications in antimicrobial coatings, surface disinfectants, food packaging, and wound healing materials.