A process for the discovery of synthetic polymer nanoparticles (NPs) with affinity and selectivity for specific peptide sequences is described. A polymer NP is used as the bait to capture a peptide that is presented by a phage library. The library used in this study was a combination of several sublibraries of phages that present peptides from 7 to 20 amino acids. The tittering result showed that the total diversity of the peptide library on the phages was 2.5 x 1010. Most peptides in the library contained 2 cysteines, which was included by design to introduce a disulfide bond into the peptide. A lightly crosslinked (2%) synthetic polymer hydrogel NP comprised of N-isopropyl acrylamide (NIPAm) monomers in addition to hydrophobic and carboxylate groups, was found to bind with high affinity to the cyclic peptide, KPCISFWQFWFGFCSS (P14C). Closely related polymer NPs including those without carboxylate groups show no interaction with P14C. Peptide conformation plays an important role in peptide-protein interactions in many biological systems. In this study, the interaction between the polymer NP and the cyclic peptide (P14C) is ~ three-fold stronger than with the linear peptide (P14L). When cysteine was mutated to serine, the modified peptide, (P14S), had a similar interaction with the NP as P14L. The result implies that the selected NP can discriminate between peptide conformations. Other proteins, such as IgG, HSA and hemoglobin show little affinity P14C suggesting that the NP selected by phage display has high specificity to P14C. To provide insight to the nature of the NP-peptide interaction and the residues that contribute importantly to binding, three phenylalanine (Phe, F) residues were mutated to asparagines (Asn, N). The triply mutated peptide (P14M), had little affinity for the NP indicating that the three aromatic amino acids play a significant role in NP binding. These results establish that phage display can be used for discovery of NPs-peptide affinity pairs. The synthetic polymer NP has high affinity and selectivity for the peptide and was able to discriminate between peptide conformations.

Peptides with selective affinity for polymer nanoparticles

248th National Meeting (2014)

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