Sequence and Structure Determinants for the Self-aggregation of Recombinant Polypeptides Modeled after Human Elastin

Abstract

Elastin is a polymeric structural protein that imparts the physical properties of extensibility and elastic recoil to tissues. The mechanism of assembly of the tropoelastin monomer into the elastin polymer probably involves extrinsic protein factors but is also related to an intrinsic capacity of elastin for ordered assembly through a process of hydrophobic self-aggregation or coacervation. Using a series of simple recombinant polypeptides based on elastin sequences and mimicking the unusual alternating domain structure of native elastin, we have investigated the influence of sequence motifs and domain structures on the propensity of these polypeptides for coacervation. The number of hydrophobic domains, their context in the alternating domain structure of elastin, and the specific nature of the hydrophobic domains included in the polypeptides all had major effects on self-aggregation. Surprisingly, in polypeptides with the same number of domains, propensity for coacervation was inversely related to the mean Kyte-Doolittle hydropathy of the polypeptide. Point mutations designed to increase the conformational flexibility of hydrophobic domains had the unexpected effect of suppressing coacervation and promoting formation of amyloid-like fibers. Such simple polypeptides provide a useful model system for understanding the relationship between sequence, structure, and mechanism of assembly of polymeric elastin.