(198c) A New Molecular Templating Approach for Controlling the Nucleation of Peptides

Frederik J. Link*^a, Jerry Y.Y. Heng^a

^aDepartment of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK

*f.link18@imperial.ac.uk

Keywords: template, polypeptide crystallisation, nucleation

Abstract

The crystallisation of bio-active polypeptides has an important significance in a wide range of medical and industrial applications since they can be used as highly effective pharmaceutical compounds [1]. The bottleneck of crystallisation is the lack of controllability of the nucleation mechanism. Templates introduce a novel way of triggering nucleation, even at low supersaturation [2]. Therefore, templates are remarkable in controlling crystallisation. Recent studies showed that by using hard templates, such as silica based porous surfaces, the induction time of nucleation of polypeptides can be significantly accelerated even if the supersaturation is super low [3]. However, the impact of the surface properties on nucleation is barely understood. It is believed that porous surfaces trigger nucleation due to local increase in supersaturation within the pores attributable to confined space rather than non-covalent interaction between the polypeptide and the surface. The approach of using small organic molecules acting as “sticky-bridges”, by linking polypeptides via non-covalent bonds, can provide new routes for crystallising polypeptides. This mechanism could reduce the surface entropy of the polypeptides rather than just increasing the supersaturation locally [4].

In this study, a simple model peptide which is known to crystallise and consists of a variety of different amino acids with different surface patches is used to investigate the influence of small organic molecules on the crystallisability. The optimal buffer-solution, pH, and precipitant have been adapted from literature and verified as optimal conditions before they were used in this study. To evaluate the impact of small organic molecules acting as seeds on the crystallisation, their chemical properties, the amount and the size of the seeds are varied. The crystallisability is investigated by means of measuring induction time, crystal yield and shape. For this purpose, hanging-drop vapour diffusion experiments will be carried out to evaluate the impact of the seeds on the nucleation.

The induction time of the seeded approach is significantly lower than the induction time for the unseeded approach, even at low supersaturation. This can be due to the specific interactions between the surface patches of the small organic molecules and polypeptides. As a result, it is believed that the chemical properties of the surface patches have a significant impact on controlling nucleation.

Further work will be done with regards to characterise the impact of the seeds with regards to surface chemistry, amount, and molecular size. Therefore characterisation of the seed surface patches and evaluation of the interaction between them and peptide will be done. Additionally, the impact of the seeds on the solubility of the peptide has to be investigated. All these findings should result ultimately in the ability of engineering seeds with application-tailored properties to specifically control the nucleation of polypeptides.

References

1. Kastin, A.J., Handbook of Biologically Active Peptides. 2 ed. 2013: Academic Press. 2032.
2. Shah, U.V., et al., Heterogeneous nucleants for crystallogenesis and bioseparation. Current Opinion in Chemical Engineering, 2015. 8: p. 69-75.
3. Shah, U.V., et al., Crystallization of Proteins at Ultralow Supersaturations Using Novel Three-Dimensional Nanotemplates. Crystal Growth & Design, 2012. 12(4): p. 1772-1777.
4. Wlodawer, A., Z. Dauter, and M. Jaskolski, ProteinCrystallography Methods and Protocols. Methods in Molecular Biology, ed. J.M. Walker. 2017, New York: Springer New York : Imprint: Humana Press.