Structure of the insect cytokine peptide plasmatocyte-spreading peptide 1 from Pseudoplusia includens

The structure of the recently identified plasmatocyte spreading peptide fro m the moth Pseudoplusia includens (PSP1) has been determined by NMR spectro scopy. This novel insect cytokine consists of 23 amino acid residues and a single disulfide bond. Torsion angle dynamics calculations utilizing a tota l of 337 distance constraints yielded an ensemble of 30 structures with an average backbone root mean square deviation for residues 7-22 of 0.18 Angst rom from the mean structure. The structure consists of a disordered N-termi nal region and a well defined core that is stabilized by numerous hydrophob ic interactions and a short beta-hairpin. Structural comparisons confirm th at PSP1 adopts an epidermal growth factor (EGF)-like fold with close simila rity to the C-terminal subdomain of EGF-like module 5 of human thrombomodul in. The combination of the three-dimensional structure of PSP1 and the exte nsive literature on EGF-receptor interactions should accelerate the process of identifying the specific residues responsible for receptor binding acti vity of this family of immunoregulatory peptides.