Solid-state NMR determination of peptide torsion angles: Applications of H-2-dephased REDOR

The backbone conformation of peptides and proteins is completely defined by the torsion angles (phi,psi,omega) of each amino acid residue along the po lypeptide chain. We demonstrate a solid-state NMR method based on heteronuc lear distance measurements for determining (phi,psi) angles. Simple and rel iable deuterium phase modulated pulses (PM5) reintroduce dipolar couplings between H-2 and a spin-1/2 nucleus. Measuring the C-13(i-1){H-2(i)alpha} RE DOR distance across a peptide bond results in the torsion angle phi (i) as a consequence of;he restricted geometry of the peptide backbone. The N-15(i +1){H-2(i)alpha} REDOR distance across a peptide bond defines the torsion a ngle psi (i). This approach is demonstrated for both the 3-spin X{H-2(2)}RE DOR case of glycine and the 2-spin X{H-2}REDOR case, represented by L-alani ne, using two different tripeptides. It is shown that the technique can han dle multiple sample conformations. PMS-REDOR decay curves of the psi angle show distinctly different behaviors between alpha -helix and beta -sheet ba ckbone conformations.