Conformational Properties of the Amphipathic Lytic Polypeptide Bombolitin-ii - A Circular-dichroism, Nmr and Computer-simulation Study

Bombolitin II is a member of a family of five structurally related heptadecapeptides, originally isolated from the venom of a bumblebee, acting at the membrane level and able to increase the activity of phospholipase A(2). The biological activity of bombolitins seems to be related to their ability to form amphipathic helical structures. To complete our systematic studies on this class of peptides, in the present work we synthesized bombolitin II by solid phase methodology. The secondary structure of this peptide was fully characterized by circular dichroism, H-1 NMR, distance geometry and molecular dynamics simulation. The peptide tends to aggregate in aqueous solution at millimolar concentrations, with formation of bundles of amphiphilic helices. In dilute aqueous solution (10(-5) mol/L) bombolitin II adopts an amphipathic helical structure in the presence of sodium dodecyl sulfate. The helical segment spans the sequence from residue 2 to residue 16. The results are in line with the hypothesis that this class of peptides modulate the acitivity of phospholipase A(2) by altering the physical state of the aggregated substrate.