Structure and Self-Assembly of Elastin-Like Peptides: A Joint Molecular Dynamics and NMR Study

Abstract

Elastin endows tissues such as skin, arterial walls, lung alveoli, and the uterus with extensibility and elasticity. Elastin and elastin-like peptides self-aggregate via a liquid-liquid phase separation process. Although elastin has been the object of biophysical investigation for over eighty years, the structural basis for the self-assembly and the mechanical properties of elastin remains controversial. Elastin is structurally heterogeneous and must be described by an ensemble of structures. As an essential step towards elucidating the structural ensemble of elastin, we combine molecular dynamics simulations and nuclear magnetic resonance (NMR) spectroscopy to study an elastin-like peptide modelled after the sequence of alternating hydrophobic and cross-linking domains of elastin. We perform extensive all-atom molecular dynamics simulations totalling hundreds of microseconds and obtain detailed structural and dynamic data by NMR on the same peptide sequences under the same thermodynamic conditions. Simulation and NMR results are in excellent agreement and show that although the peptide is highly disordered, it possesses a significant propensity for secondary structure. The cross-linking domains are characterized by fluctuating helical structure, whereas the hydrophobic domains adopt fluctuating hydrogen-bonded turns. The latter secondary structure elements are sparse, local, and transient. As a result, the individual domains do not form extensive interactions; they are collapsed but not compact, and they remain disordered and hydrated despite their predominantly hydrophobic character. Taken together, these findings resolve long-standing discrepancies between previous models of the structure and function of elastin. Importantly, these results also afford unprecedented insight into the physical and structural basis for the liquid-liquid phase separation of disordered proteins.