C-13 MULTIPLET NUCLEAR-MAGNETIC-RESONANCE RELAXATION-DERIVED RING PUCKERING AND BACKBONE DYNAMICS IN PROLINE-CONTAINING GLYCINE-BASED PEPTIDES

(CH2)-C-13-multiplet nuclear magnetic resonance relaxation studies on proline (P)-containing glycine (G)-based peptides, GP, PG, GPG, PGG, a nd GPGG, provided numerous dipolar auto- and cross-correlation times f or various motional model analyses of backbone and proline-ring bond r otations. Molecular dynamics simulations and bond rotation energy prof iles were calculated to assess which motions could contribute most to observed relaxation phenomena. Results indicate that proline restricts backbone Psi(1), Psi(2), and phi(2) motions by 50% relative to those found for a polyglycine control peptide. Psi(1) rotations are more res tricted in the trans-proline isomer state than in the cis form. A two- state jump model best approximates proline ring puckering which in wat er could occur either by the C-gamma endo-exo or by the C2 interconver sion mechanism. The temperature dependence (5 degrees to 75 degrees C) of C-beta, and C-gamma, and C-delta angular changes is rather flat, s uggesting a near zero enthalpic contribution to the ring puckering pro cess. In lower dielectric solvents, dimethylsulfoxide and methanol, wh ich may mimic the hydrophobic environment within a protein, the endo-e xo mechanism is preferred.