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 beta-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 beta- nor a gamma-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.