Polysialic acid (PSA) is a unique post-translational modification found on the neural cell adhesion molecule (NCAM) and plays an important physiological role in nervous system development by modulating neuronal interactions. While the size and hydrophilicity of PSA result in a large excluded volume that serves its non-adhesive properties well, key lectins are known to interact specifically, albeit with low affinity, to this anionic homopolymer. In addition to facilitating understanding of the biochemistry of PSA, knowledge of biomolecular interactions involving PSA may be exploited in targeting of this glycan in biotechnological applications, as for the development of ligands, such as peptides, to serve as biosensors, modulators in infections caused by PSA-expressing microbes, or novel affinity agents for neural stem cell targeting. We present here an approach to rationally develop PSA-binding peptides through a study of PSA interaction with Siglec-11, a selective lectin for alpha-2,8-linked N-acetylneuraminic acid. In addition to being small, stable molecules amenable to small-molecule modification, peptides offer the possibility to study and exploit natural interactions as the basis for rational design. Complemented with multiple peptide design strategies, the natural interactions-based approach, built upon epitope mapping of Siglec-11, has enabled verification of the PSA-Siglec-11 binding pocket and identified lead peptide candidates. High-throughput synthesis and screening of peptide libraries in microarray format enabled identification of such candidates and determination of affinity and selectivity of peptide interaction with PSA. Library level data support the notion of low affinity carbohydrate-peptide interactions, where spatial positioning of positively charged residues together with weak hydrophobic interactions governs selective binding. Lead peptides were further studied using high-throughput platforms through mutational analyses for examination of critical binding residues. Additionally, peptide-PSA interaction was studied using surface plasmon resonance (SPR) spectroscopy and fluorescence anisotropy assays. The approach used in development and study of PSA-binding peptides thus contributes to the understanding of carbohydrate-peptide interactions and has implications for small-molecule targeting of specific glycosylation patterns in disease-related applications.

Rational design and study of polysialic acid-binding peptides

253rd National Meeting (2017)

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