Structural requirements essential for elastin coacervation: Favorable spatial arrangements of valine ridges on the three-dimensional structure of elastin-derived polypeptide (VPGVG)n

The elastin precursor tropoelastin possesses a number of polymeric peptides with repeating 3-9 mer sequences. One of these is the pentapeptide Val-Pro-Gly-Val-Gly (VPGVG) present in almost all animal species, and its polymer (VPGVG)n coacervates just as does tropoelastin. In the present study, in order to explore the structural requirements essential for coacervation, (VPGVG)n and its shortened repeat analogs (VPGV)n, (VPG)n, and (PGVG)n were synthesized and their structural properties were investigated. In our turbidity measurements, (VPGVG)n demonstrated complete reversible coacervation in agreement with previous findings. The Gly ⁵-deleted polymer (VPGV)n also achieved self-association, though the onset of self-association occurred at a lower temperature. However, the dissociation of (VPGV)n upon temperature lowering was found to occur in a three-step process; the Val _i ⁴-Val _i+1 ¹ structure arising in the VPGV polypeptide appeared to perturb the dissociation. No self-association was observed for (VPG)n or (PGVG)n repeats. Spectroscopic measurements by CD, FT-IR, and ¹H-NMR showed that the (VPGV)n and (VPG)n both assumed ordered structures similar to that of (VPGVG)n. These results demonstrated that VPGVG is a structural element essential to achieving the β-spiral structure required for self-association followed by coacervation, probably due to the ideal spatial arrangement of the hydrophobic Val residues.