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

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The structure of an elastin-mimetic model peptide, (VPGVG)6, was proposed by combining data obtained from quantitative use of the conformation-dependent 13C 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 13C, 15N 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 (φ, ψ) = (−90 ± 15°, 120 ± 15°). In contrast, bimodal distributions for the central residues of the (VPGVG) subunit were detected. For Pro-12, (φ, ψ) = (−60 ± 15°, 120 ± 15°), 80%, and (φ, ψ) = (−60 ± 15°, −30 ± 15°), 20%; for Gly-13, (φ, ψ) = (90 ± 30°, −15 ± 30°) and (φ, ψ) = (−90 ± 15°, 0 ± 15°), 60%, and (φ, ψ) = (−105 ± 75°, 150 ± 30°), (φ, ψ) = (120 ± 60°, 150 ± 30°), (φ, ψ) = (−120 ± 60°, −150 ± 30°) and (φ, ψ) = (120 ± 60°, −150 ± 30°), 40%. For Val-14, (φ, ψ) = (−110 ± 20°, 130 ± 20°), 70%, and (φ, ψ) = (−75 ± 15°, −15 ± 15°) 30%. To reconcile the torsion angles corresponding to the main component in the conformational distributions, a type-II β-turn structure was assigned to about 40% of the Pro-Gly pair.