Evaluation of conformation and association behavior of multivalent alanine-rich polypeptides

Purpose. Helical alanine-rich polypeptides with functional groups displayed along the backbone can display desired molecules such as saccharides or therapeutic molecules at a prescribed spacing. Because these polypeptides have promise for application as biomaterials, the conformation and association of these molecules have been investigated under biologically relevant conditions. Methods. Three polypeptide sequences, 17-H-3, 17-H-6, and 35-H-6, have been produced through recombinant techniques. Circular dichroic (CD) spectroscopy was used to monitor the secondary structure of the polypeptides in PBS (phosphate buffered saline, pH 7.4). The aggregation behavior in PBS was monitored via analytical ultracentrifugation and non-denaturing polyacrylamide gel electrophoresis. Results. The three polypeptides adopt a highly helical structure at low and ambient temperatures, and when heated, undergo a helix-to-coil transition, typical of other alanine-rich peptide sequences. The melting temperatures and van't Hoff enthalpies, extracted from the CD data, suggest similar stability of the sequences. Although alanine-rich sequences can be prone to aggregation, there is no indication of aggregation for the three polypeptides at a range of concentrations relevant for possible biological applications. Conclusions. The helical polypeptides are monomeric under biologically relevant conditions enabling application of these polypeptides as useful scaffolds for ligand or drug display.