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Prattley, Charlotte Emma (2019) Engineering lantibiotic-inspired chimeric antimicrobials. PhD thesis, University of Nottingham.

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Abstract

Microbial control is important in both human health and food safety. Naturally occurring antimicrobial peptides, such as nisin, have been used extensively to preserve a variety of food products, yet resistance remains uncommon. Both food protection and medical applications urgently require the development of new chimeric antimicrobials, inspired by natural compounds. Ideal antimicrobial peptides possess both specific recognition of targets found universally in bacteria and low haemolytic activity.

We propose to engineer lantibiotic-inspired, lipid II targeting engaging short peptides and chimeric antimicrobials with a targeting domain and a pore forming moiety. This study analyses the properties of candidate compounds N12L, N12D, N12LM2 and N12DM2. N12 represents a section inspired by the first 12 residue target-recognition motif of the common food preservative and antimicrobial nisin. D/L denotes cysteine chirality at position 3 and 7. M2 depicts the presence of magainin II, a pore forming antimicrobial with poor target recognition. Two disulphide bridges can construct macro-cyclic peptides, mimicking rings A and B of nisin.

Interaction of the N12D motif is independent of its cyclisation state. Fluorescent microscopy showed that semi-cyclic N12D binds extensively to Bacillus subtilis. Cyclic N12DM2 displayed reduced leakage in the presence of lipid II, but not geranyl geranyl pyrophosphate (GGPP) and showed thermally stable interaction with N-acetylmuramyl-L-alanyl-D-isoglutamine hydrate (MurNAc-dipeptide) through CD studies. Linear N12DM2 was inactive against Micrococcus luteus unless combined with PGLa (peptide with N-terminal glycine and C-terminal leucinamide), a peptide within the magainin family. This suggests that peptides with the N12D motif bind to MurNAc-dipeptide and in the case of the N12DM2 this prevents the action of magainin II.

Antimicrobial activity was demonstrated by cyclic N12L against M. luteus and foodborne pathogens Listeria monocytogenes and Staphylococcus spp., while its linear form is mostly inactive at comparable concentrations. This shows that for N12L to be active it needs to be cyclised. When evaluated against components of lipid II, cyclic N12LM2 displayed interaction with isopentenyl pyrophosphate (I-PP) but did not interact with MurNAc-dipeptide. Some interaction was seen for linear N12L and I-PP, suggesting that increased interaction of N12L with pyrophosphates occurs as the degree of cyclisation increases. This is supported by the fluorescence microscopy, as semi-cyclic N12L-TAM binds B. subtilis. In conclusion, cyclised N12L has the most potential as an antimicrobial out of the peptides synthesised and properties assessed.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Bonev, Boyan Ryun-Drasbek, Mette Williams, Paul
Keywords:	Antimicrobial, Food Preservation, Nisin, Lantibiotic
Subjects:	Q Science > QR Microbiology
Faculties/Schools:	UK Campuses > Faculty of Medicine and Health Sciences > School of Life Sciences
Item ID:	57291
Depositing User:	Prattley, Charlotte
Date Deposited:	28 Jul 2025 11:32
Last Modified:	28 Jul 2025 12:33
URI:	https://eprints.nottingham.ac.uk/id/eprint/57291

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