CIRCULAR-DICHROISM AND FLUORESCENCE STUDIES ON MELITTIN - EFFECTS OF C-TERMINAL MODIFICATIONS ON TETRAMER FORMATION AND BINDING TO PHOSPHOLIPID-VESICLES

Studies were performed on a series of melittin analogues with selectiv e alterations to the positively charged amino acid sequence at the C-t erminus. Fluorescence studies were undertaken using the sole tryptopha n residue in the analogues as an intrinsic fluorescence probe for indi cations of tetramer formation in free solution, and binding and insert ion of the melittins into phospholipid bilayers. Studies were performe d under conditions of lowsalt buffer with increasing concentrations of phosphate added to promote self-association of the melittin monomers, and also in the presence of phospholipid vesicles. C.d. studies were also performed under conditions of increasing phosphate concentrations and in the presence of lipid vesicles to monitor the alpha-helical co ntent of the melittins. It was found that selective replacement of the C-terminal basic amino acids by glutamine has different effects on se lf-association, alpha-helix formation and lipid binding of melittin,