Conformational change on calcium binding by the lipopeptide antibiotic amphomycin. A C.D. and monolayer study

The acidic linear lipopeptide amphomycin is a calcium dependent antibiotic which is thought to bind to carrier lipids such as dolichol monophosphate. The actual role of Ca++ is not definitely established and in this article we have examined the peptides interactions with a range of divalent cations. By CD we have shown that a conformational change is induced by Ca++, Sr++ and Ba++ but not by Mg++, Zn++, Cd++ or Gd+++. Monolayer studies show a decrease in molecular area and an increase in film stability when the subphase contains Ca++. The ensemble of results provides preliminary evidence for the formation of a beta hairpin structure on ion binding (Ka (Ca++) = 2.4 x 10(3)M-1) which could enhance amphomycin's bilayer solubility.