SOLUTION CONFORMATION OF AN ANTIBACTERIAL PEPTIDE, SARCOTOXIN-IA, AS DETERMINED BY H-1-NMR

The solution conformation of sarcotoxin IA, which is an antibacterial peptide isolated from Sarcophaga peregrina with a molecular mass of 4 kDa, was determined by NMR spectroscopy and hybrid distance geometry/dynamical simulated annealing calculations. On the basis of 227 experimental constraints, including 185 distance constraints obtained from NOE and 42 constraints associated with 21 hydrogen bonds, a total of 18 converged structures of sarcotoxin IA were obtained. The final 18 converged structures exhibit backbone-atomic root-mean-square differences about the averaged coordinate positions of 0.070 +/- 0.027 nm for residues 3 - 23 and 0.040 +/- 0.017 nm for residues 28-38. It has been indicated that sarcotoxin IA consists of two amphiphilic alpha-helical regions, i.e. helix I (Leu3 - Gln23) and helix II (Ala28 - Ala3 8), with a hinge region (Gly24 - Ile27), which connects helix I and helix II. We conclude that these two amphiphilic helical segments of sarcotoxin IA are of importance for the expression of the antibacterial activity.