The study of solution conformation of allatostatins by 2-D NMR and molecular modeling

More than 70 allatostatins have been isolated from various insects and there is interest in the determination of their active conformation. We have synthesized Dippu-AST 1 (originally isolated from the cockroach Blattella germanica) and studied its conformation in solution by 2-D NMR and molecular modeling. Dippu-AST 1 belongs to the cockroach-type ASTs that have Y/FXFGL-NH2 as the common C-terminal sequence. We found that Dippu-AST 1 forms a type I' β-turn conformation in DMSO. We also studied the conformations of Dippu-AST 1 and six cockroach-type allatostatins in water using the molecular dynamics method. When the X amino acid in the consensus sequence Y/FXFGL-NH2 is Ala or Ser, the allatostatin can form a typical type II β-turn. If the X is Asp or Asn whose side chain contains a carbonyl, the allatostatin can form a type I, I' or IV β-turn conformation; if the X is Gly, a closer γ-turn is adopted. Our study indicates that the turn conformation is ubiquitous in cockroach-type allatostatins.