Structural behavior of polypeptides in solution are dependent on their sequence. Amino acids contain different side chains so changing their sequence induces different interactions between their side chains, altering their structure. Some peptides are known to inhibit or facilitate biological functions through protein binding. Through biological assays, it has been shown that a pentapeptide containing the repeats of ADV prefers to bind to Caspase 2, an enzyme that plays a critical role involved in cell apoptosis. A library of 16 peptides were synthesized on a CEM microwave peptide synthesizer having the sequence AXVX’XVG, where X = D, E, K, or O and X’ = A, F, G, or L. High resolution, solution two-dimensional (2D) NMR spectroscopic experiments were done using a combination of total correlation spectroscopy (TOCSY) and rotating frame nuclear Overhauser effect spectroscopy (ROESY). This aided in understanding the structural behavior and properties of these polypeptides in solution. SPARKY was used to assign peaks and calculate peak volumes from ROESY data, which were further utilized to calculate an ensemble of structures with CYANA. Variable temperature (VT) NMR experiments between the temperature range of 25-50 °C provided the amide temperature coefficients, indicating the extent of hydrogen bonding in the peptide chain. The side chains of the peptide structures that have bulkier, non-polar R groups, such as phenylalanine and leucine, have less interaction with the charged residues (X). In all peptide sequences the valine’s positions are conserved, so they are good comparisons for temperature coefficients. Changing the length of the side chain from aspartic acid to glutamic acid, and from lysine to ornithine alters the hydrogen bonding pattern in these peptides. Studies of this small library of peptides will provide insight into how point mutation in these polar peptides can modulate their structural behavior that could affect protein inhibition characteristics.

Structural studies of charged heptapeptides with point mutations using solution state two-dimensional NMR spectroscopy

2019 Fall National Meeting

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