Structure and Dynamics of Two Elastin-like Polypentapeptides Studied by NMR Spectroscopy

Abstract

The structure and dynamics of two synthetic elastin-like polypentapeptides, poly(G₁V₁G₂V₂P) and poly(AV₁GV₂P), were studied in D₂O and H₂O at various temperatures by using ¹H, ²H,¹³C, and ¹⁵N NMR spectra, relaxations, and PGSE self-diffusivity measurement. Signal assignments were made using COSY, NOESY, HXCORR, HSQC, HMBC, and SSLR INEPT techniques. Temperature-induced conformation changes were studied using ³J_NHCH couplings, NOESY connectivity, chemical shifts, and signal intensities. Hydrodynamic radii were derived from self-diffusion coefficients measured by the pulsed-gradient spin−echo (PGSE) method. Selective hydration (hydrophilic or hydrophobic) was explored using NOESY and ROESY spectral methods and longitudinal and transverse ¹H relaxation of HOD and quadrupolar ²H relaxation of D₂O. Four different physical states were discerned in different temperature regions for both polymers: state I of a rather extended, statistically shaped and fully hydrated polymer below the critical temperature (approximately 299−300 K); state II, a relatively coiled and globular but disordered preaggregation state, developing in a rather narrow region, 300−303 K, in the case of poly(AV₁GV₂P) and in a broader region, overlapping with the next one, in poly(G₁V₁G₂V₂P); state III, a tightly coiled, more compact state in the region 303−313 K; and, finally, state IV, an aggregated (and eventually flocculating and sedimenting) state beyond 313 K. States II−IV coexist in varying proportions in the whole temperature range above 299 K. A structure characterized by a β-turn stabilized by H-bonding between the Ala carbonyl and Val₂ NH groups of poly(AV₁GV₂P) was detected by NOESY just above the transition temperature. States II and III are progressively more stripped of their hydration sheath but retain some molecules of water confined and relatively immobilized in their coils.