Structural determination of an elastin-mimetic model peptide, (Val-Pro-Gly-Val-Gly)6, studied by 13C CP/MAS NMR chemical shifts, two-dimensional off magic angle spinning spin-diffusion NMR, rotational echo double resonance, and statistical distribution of torsion angles from protein data bank

The structure of an elastin-mimetic model peptide, (VPGVG)6, was proposed by combining data obtained from quantitative use of the conformation-dependent C-13 NMR chemical shifts, two-dimensional off magic angle spinning spin-diffusion solid-state NMR with 13C double labeling of the peptides, rotational-echo double-resonance of C-13, N-15 double labeling peptides, and statistical distribution of the backbone torsion angles of Val-Pro, Pro-Gly, and Gly-Val-Gly sequences from PDB. In essence, this approach drew upon several sets of data to formulate the resulting model, namely, that there is a distribution of conformations in this polypeptide. The Val-16 residue adopts torsion angles (phi, psi) = (-90 +/- 15 degrees, 120 +/- 15 degrees). In contrast, bimodal distributions for the central residues of the (VPGVG) subunit were detected. For Pro-12, (phi, psi) = (-60 +/- 15 degrees, 120 +/- 15 degrees), 80%, and (phi, psi) = (-60 +/- 15 degrees, -30 +/- 15 degrees), 20%; for Gly-13, (phi, psi) = (90 +/- 30 degrees, -15 +/- 30 degrees) and (phi, psi) = (-90 +/- 15 degrees, 0 +/- 15 degrees), 60%, and (phi, psi) = (-105 +/- 75 degrees, 150 +/- 30 degrees), (phi, psi) = (120 +/- 60 degrees 150 +/- 30 degrees), (phi, psi) = (-120 +/- 60 degrees, -150 +/- 30 degrees) and (phi, psi) = (120 +/- 60 degrees, -150 +/- 30 degrees), 40%. For Val-14, (phi, psi) (-110 +/- 20 degrees, 130 +/- 20 degrees), 70%, and (phi, psi) = (-75 +/- 15 degrees, -15 +/- 15 degrees) 30%. To reconcile the torsion angles corresponding to the main component in the conformational distributions, a type-II beta-turn structure was assigned to about 40% of the Pro-Gly pair.