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4 1 I H I G H L I G H T S 2 0 2 3

PRINCIPAL PUBLICATION AND AUTHORS

Stability of Nanopeptides: Structure and Molecular Exchange of Self-assembled Peptide Fibers, N. König (a,b), S.M. Szostak (a), J.E. Nielsen (a), M. Dunbar (c), S. Yang (d), W. Chen (d), A. Benjamin (c), A. Radulescu (e), N. Mahmoudi (f), L. Willner (b), S. Keten (c,g), H. Dong (d), R. Lund (a,h), ACS Nano 17, 12394-12408 (2023); https:/doi.org/10.1021/acsnano.3c01811 (a) Department of Chemistry, University of Oslo (Norway) (b) Jülich Centre for Neutron Science (JCNS-1) and Institute for Biological Information Processing (IBI-8), Forschungszentrum Jülich, Jülich (Germany) (c) Department of Mechanical Engineering, Northwestern University, Illinois (USA) (d) Department of Chemistry & Biochemistry, The University of Texas at Arlington (USA) (e) Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich, Garching (Germany) (f) ISIS-STFC, Rutherford Appleton Laboratory, Chilton (UK) (g) Department of Civil and Environmental Engineering, Northwestern University, Illinois (USA) (h) Hylleraas Centre for Quantum Molecular Sciences, University of Oslo (Norway)

REFERENCES

[1] D. Xu et al., Chem. Commun. 51, 1289-1292 (2015). [2] J.E. Nielsen et al., Curr. Opin. Colloid Interface Sci. 66, 101709 (2023). [3] J.E. Nielsen et al., RSC Adv. 10, 35329-35340 (2020).

charges. The results show that the nanostructure was destabilised, manifested by susceptibility to changes in pH and temperature. This shows that there is a delicate balance in the intermolecular interactions leading to stability, while lysine is required to maintain the antimicrobial activity. [3]

Extraordinarily stable proteins can be found in nature, for example, inside thermophilic bacteria such as Bacillus stearothermophilus and Thermus aquaticus. This work finds that relatively short peptide sequences can form exceptionally stable superstructures, which can be used, for instance, as antibiotics. These assemblies are more resistant toward enzymatic degradation and non-specific protein clearance, providing longer blood circulation and in-situ stability in various biomedical applications.

Fig. 26: a) Illustration of the SANS method.

b) Time-resolved scattering (TR-SANS)

curves showing arrested structures

at 37°C. Dotted line corresponds to fully

mixed peptides (end- state). c) Illustration of

non-existing peptide exchange. d) TR-SANS data showing that the nanostructure can be

partially broken up with extensive sonication.

The peptides were further investigated via time-resolved SANS using a contrast method yielding the molecular mixing of the peptide residues constituting the sheets visible. The technique, illustrated in Figure 26a, is based on mixing deuterated ( black ) and protiated ( white ) peptides in zero average contrast conditions ( grey , about 1:1 H2O/D2O mixtures). This renders the molecular exchange (i.e., the release and uptake of peptides) visible by leading to a decay in the scattered intensity. The data show that no visible exchange kinetics takes place at temperatures up to 90°C (Figure 26b-c). Only upon harsh treatment, using extensive tip sonication, is a limited decay in intensity observed, showing that some peptides are released from the nanostructure (Figure 26d).

In order to gain further insight into the governing molecular interactions, the cohesive binding energy was extracted from simulations using molecular mechanics with the generalised Born and surface area solvation (MM/GBSA) method. The results show a total binding energy of 319 kJ/mol where leucine hydrophobic contributions dominate together with the hydrogen bonds from glutamine, while electrostatic repulsions created by lysines contributed negatively to the overall stability. This was elucidated in more detail by designing peptides with additional lysine