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oai:figshare.com:article/32805749 2026-10-01T16:13:29Z portal_1172 item_type_8 month_year_10_2026

Acquisition, characterisation and modification of bioactive peptides from skin secretion of Rana dybowskii Xinran Geng (5863940) PUREID: 688025507 Antimicrobial peptides Rana dybowskii skin secretion structure-activity relationship antimicrobial mechanism The mortality caused by antimicrobial resistance (AMR) will rise from 0.7 million per year to 10 million a year by 2050, leading to the urgent need for substitutes for antibiotics to defeat the antibiotic-resistant pathogens. Antimicrobial peptides (AMPs) were chosen as the potential alternatives due to their non-specific targets on membranes that are thus less likelihood of causing genetic mutation and resistance. Meanwhile, the leading cause of death in the world, cancer, was reported to be possibly-treatable with peptides due to the similar mechanism of electrostatic interaction. Amphibians like Rana dybowskii, are recognised as a rich source of AMPs. In this study, Brevinin-2DYf, a novel peptide from the skin secretion of Rana dybowskii, was discovered through molecular cloning and identified as having dual activity of antimicrobial efficacy and antiproliferative effect against cancer cells. To further analyse the structure-activity relationship of this species, two more peptides from Rana dybowskii, named Dybowskin-4 and Japonicin-1CDYa, from previous publications, were likewise further studied. Aimed at improving the therapeutic index (TI) value, a series of analogues of each peptide were designed and structure-activity relationships were analysed simultaneously through functional assays and mechanism investigations. Structure-activity analysis of Brevinin-2DYf and its analogues revealed that only one L to V modification was the optimal strategy for balancing safety and efficacy with the greatest TI value (TI values of 10V were Gram+: 92.06, Gram-: 149.20 and yeast for 16.23; while those of Brevinin-2DYf were Gram+:24.25, Gram-: 26.10 and yeast for 2.14). In addition, the modified Japonicin-1CDYa, A5K, was shown to enhance antimicrobial activity of parent peptide and possessed approximately 8-fold of the TI value (TI values of Japonicin-1CDYa were Gram+: 0.15 and Gram-: 0.06 and Geometric mean of Japonicin-1CDYa were GMGram+: 9.51µM and GMGram-: 23.51µM; while those of A5K were Gram+: 0.85 and Gram-: 0.53 with GMGram+: 6.73µM and GMGram-:10.89µM). Amazingly, the maintained activity and decreased haemolytic toxicity of analogue, V7L I14K of Dybowskin-4, may indicate the importance of maintaining hydrophobicity (TI values of Dybowskin-4 were Gram+: 1.01 and Gram-: 0.23; while those of V7L I14K were Gram+: 10.70 and Gram-:4.01; and Dybowskin-4: 8µM in GMGram+ and 34.56µM in GMGram-; V7L I14K: 9.51µM in GMGram+ and 25.39µM in GMGram-). Additionally, the necessity of the Rana box was also confirmed from different perspectives for each peptide: a truncated Brevinin-2DYf had decreased antimicrobial activity, Dybowskin-4’ s analogues with I8 modified (adjacent position to ana box) exhibited greater changes in activity and the severely-increased MIC value of F to A changes in position 11 (in the Rana box) in Japonicin-1CDYa. These discoveries enriched the structure-activity analysis of the mentioned superfamilies of AMPs, respectively, and provided the peptide database with more characteristics of AMPs from the skin secretion of Rana dybowskii, confirming the idea that modification of natural AMPs can be further utilised as a strategy for generation of candidate antimicrobial agents as a pipeline for future clinical trials. Thesis is embargoed until 31 July 2031. 2026-10-01T16:13:29Z Text Thesis 10.17034/32805749.v1 https://figshare.com/articles/thesis/Acquisition_characterisation_and_modification_of_bioactive_peptides_from_skin_secretion_of_Rana_dybowskii/32805749 All Rights Reserved Open Access after 2031-07-31