Investigation of the dynamics of an elastin‐mimetic polypeptide using solid‐state NMR

Abstract

Elastin is the main structural protein that provides elasticity to various tissues and organs in vertebrates. Molecular motions are believed to play a significant role in its elasticity. We have used solid-state NMR spectroscopy to characterize the dynamics of an elastin-mimetic protein as a function of hydration to better understand the origin of elastin elasticity. Poly(Lys-25), [(VPGVG)(4)(VPGKG)](39), has a repeat sequence common to natural elastin. (13)C cross-polarization and direct polarization spectra at various hydration levels indicate that water enhances the protein motion in a non-uniform manner. Below 20% hydration, the backbone motion increases only slightly whereas above 30% hydration, both the backbone and the side-chains undergo large-amplitude motions. The motional amplitudes are extracted from (13)C-(1)H and (1)H-(1)H dipolar couplings using 2D isotropic-anisotropic correlation experiments. The root mean square fluctuation angles are found to be 11-18 degrees in the dry protein and 16-21 degrees in the 20% hydrated protein. Dramatically, the amplitudes increase to near isotropic at 30% hydration. Field-dependent (1)H rotating-frame spin-lattice relaxation times (T(1rho)) indicate that significant motions occur on the microsecond time-scale (1.2-2.3 micros). The large-amplitude and low-frequency motion of poly(Lys-25) at relatively mild hydration indicates that the conformational entropy of the protein in the relaxed state contributes significantly to the elasticity.

Studying natural structural protein fibers by solid‐state nuclear magnetic resonance

“…In addition, highly mobile glycine residues could be resolved in two different environments (113). The comparison of 13 C CP and DP spectra also allowed observing a similar stepwise behavior upon hydration in an elastin model compound (105).…”

“…For instance, various models have been suggested which could account for the entropic contribution to elasticity in fibers. These include changes in conformational freedom, vibrational motions of parts of the protein backbone, or changes in hydrophobic side chain exposure to water (5,104,105). Solid-state NMR is a first-rate technique to investigate the dynamics of natural protein fibers because it can scrutinize a variety of motional domains, including crystalline and amorphous.…”

“…The same applies to T 1r values; 1 H-T 1r are obtained by a simple CP with variable contact time followed by 13 C detection, and 13 C-T 1r by a classical crosspolarization step followed by a variable 13 C spin-lock time prior to its detection (108). To select protons which are directly bonded to the observed 13 C, the cross-polarization step was replaced in a recent work by a Lee-Goldburg CP which reduces spin diffusion effects (105).…”

Conformational Transitions of the Cross-linking Domains of Elastin during Self-assembly

“…Hydrophobic domains are rich in nonpolar amino acids such as proline, glycine, valine, and leucine. These domains have been shown by experiment and molecular dynamics simulations to be highly disordered and flexible in solution (3)(4)(5)(6)(7)(8)(9). The high entropy and hydrophobic character of these domains is believed to be responsible for the extensibility and restoring force of polymeric elastin (6, 10 -12).…”

High resolutionq‐space imaging studies of water in elastin

“…17 Several NMR dynamic studies have also pointed to elastin being highly mobile with the association of water. [18][19][20] The NMR relaxation times of waters of hydration in elastin have been studied, and it was suggested that two distinct water components exist within elastin fibers; tightly bound waters of hydration in addition to water having more ''bulk-like'' properties reminiscent of free water. 21 In this work, our goal is to further understand the dynamics of water within elastin fibers by q-space NMR imaging.…”