Simulations of conformers of tuftsin and a cyclic tuftsin analog

The conformational properties of the configurational isomers of tuftsin, a linear tetrapeptide with the sequence Thr‐Lys‐Pro‐Arg, were investigated with six 1 ns molecular dynamics simulations in explicit water and in a 1.0 M NaCl solution. The average conformation of the cis isomer is a type VI β‐turn. Our results indicate that water‐peptide hydrogen bonding, in addition to intramolecular hydrogen bonds, stabilizes the cis conformer. The trans isomer is neither a β‐ nor a γ‐turn. Results are compared with parallel studies on a cyclic analog of tuftsin, cyclo(Thr‐Lys‐Pro‐Arg‐Gly). The addition of salt does not influence the backbone conformation of the peptide. Differences between the structures are confined to the side‐chain orientations of the Lys and Arg residues. © Munksgaard 1995.