Structure Distribution in an Elastin-Mimetic Peptide (VPGVG)3 Investigated by Solid-State NMR

Elastin is an extracellular-matrix protein that imparts elasticity to tissues. We have used solid-state NMR to determine a number of distances and torsion angles in an elastin-mimetic peptide, (VPGVG)3, to understand the structural basis of elasticity. C−H and C−N distances between the V6 carbonyl and the V9 amide segment were measured using 13C−15N and 13C−1H rotational-echo double-resonance experiments. The results indicate the coexistence of two types of intramolecular distances: a third of the molecules have short C−H and C−N distances of 3.3 ± 0.2 and 4.3 ± 0.2 Å, respectively, while the rest have longer distances of about 7 Å. Complementing the distance constraints, we measured the (φ, ψ) torsion angles of the central pentameric unit using dipolar correlation NMR. The ψ-angles of P7 and G8 are predominantly ∼150°, thus restricting the majority of the peptide to be extended. Combining all torsion angles measured for the five residues, the G8 Cα chemical shift, and the V6−V9 distances, we obtained a bimodal structure distribution for the PG residues in VPGVG. The minor form is a compact structure with a V6−V9 CO−HN hydrogen bond and can be either a type II β-turn or a previously unidentified turn with Pro (φ = −70°, ψ = 20 ± 20°) and Gly (φ = −100 ± 20°, ψ = −20 ± 20°). The major form is an extended and distorted β-strand without a V6−V9 hydrogen bond and differs from the ideal parallel and antiparallel β-strands. The other three residues in the VPGVG unit mainly adopt antiparallel β-sheet torsion angles. Since (VPGVG)3 has the same 13C and 15N isotropic and anisotropic chemical shifts as the elastin-mimetic protein (VPGXG) n (X = V and K, n = 195), the observed conformational distribution around Pro and Gly sheds light on the molecular mechanism of elastin elasticity.