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 C-13-N-15 and C-13-H-1 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 Angstrom, respectively, while the rest have longer distances of about 7 Angstrom. Complementing the distance constraints, we measured the (phi, psi) torsion angles of the central pentameric unit using dipolar correlation NMR. The psi-angles of P7 and G8 are predominantly similar to150degrees, thus restricting the majority of the peptide to be extended. Combining all torsion angles measured for the five residues, the G8 Calpha 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-H-N hydrogen bond and can be either a type 11 beta-turn or a previously unidentified turn with Pro (phi = -70degrees, psi = 20 +/- 20degrees) and Gly (phi = -100 +/- 20degrees, psi = -20 +/- 20degrees). The major form is an extended and distorted P-strand without a V6-V9 hydrogen bond and differs from the ideal parallel and antiparallel beta-strands. The other three residues in the VPGVG unit mainly adopt antiparallel beta-sheet torsion angles. Since (VPGVG)3 has the same C-13 and N-15 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.