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.
Copyright 2004 John Wiley & Sons, Ltd.