FTIR study of the monosialoganglioside GM(1) in perdeuterated dimyristoylglycerophosphocholine (DMPCd54) multilamellar bilayers: Spectroscopic evidence of a significant interaction between Ca2+ ions and the sialic acid moiety of GM(1)

Fourier transform infrared (FTIR) spectroscopy was employed to study bovine brain GM(1) and perdeuterated dimyristoylglycerophosphocholine (DMPCd54) m ultilamellar dispersions (mole fractions of GM(1) in DMPCd54: 0.12, 0.15, 0 .19, 0.26, 0.34, 0.41, and 0.58), in the absence and presence of 10 mM CaCl 2. GM(1) micelles did not display a thermal phase transition in the tempera ture range 5-60 degrees C. Moreover, the ceramide moiety of GM(1) inserted into the hydrophobic core of DMPCd54 bilayers and was capable of undergoing a single, cooperative phase transition (T-m = 22-28 degrees C, depending o n GM(1) content) in a bilayer system. This suggested that the mixed bilayer s consisted of a homogeneous mixture and that GM(1) was uniformly dispersed in the bilayer plane rather than segregated into regions of relative enric hment, The coexistence of GM(1) and DMPCd54 in a bilayer environment induce d a rearrangement of the interfacial hydrogen bonding network of the amide I and ester C=O groups, relative to GM(1) micelles and DMPCd54 bilayers, re spectively. The modifications induced by GM(1) might ultimately modulate su rface events such as lipid-lipid and/or lipid-protein interactions. The spe ctroscopic results also suggested that the glycolipid's headgroup surface l ocation and conformation in bilayers allow GM(1) to act as a receptor for C a2+ via its sialic acid moiety.