Interactions of proteins with ganglioside-enriched microdomains on the membrane: the lateral phase separation of molecular species of GD1a ganglioside, having homogeneous long-chain base composition, is recognized by Vibrio cholerae sialidase.
The thermotropic behavior (studied by high-sensitivity differential scanning calorimetry) and susceptibility to Vibrio cholerae sialidase hydrolysis of large unilamellar vesicles of dipalmitoyl-phosphatidylcholine, containing native GD1a ganglioside or the molecular species of GD1a containing C18:1 or C20:1 long-chain base (C18:1 GD1a; C20:1 GD1a), were studied. Vesicles containing ganglioside (10% in molar terms) showed the presence in the heat capacity function of a second minor peak besides the phospholipid main transition peak. The presence of a second peak is much more evident with C20:1 GD1a than with C18:1 GD1a, the difference being potentiated by Ca2+ and indicating a different tendency of the CD1a molecular species to undergo lateral phase separation. The scans of vesicles containing native GD1a showed the features of those obtained with C18:1 GD1a and C20:1 GD1a, indicating that the main components of native GD1a, C18:1 GD1a and C20:1 GD1a, maintain their individual aggregative properties. V. cholerae sialidase affects vesicle-bound GD1a at a much higher rate (17-25-fold) than it does micellar GD1a, the activation by Ca2+ being 3- and 2-fold, respectively. The Vmax values were identical on C18:1 GD1a and C20:1 GD1a in micellar dispersions, whereas they were markedly higher (from 20 to 50%) on C18:1 GD1a than on C20:1 GD1a in vesicular dispersions. Exhaustive sialidase hydrolysis of vesicles carrying native GD1a produced C18:1 GM1 and C20:1 GM1 in the same proportion as the C18:1 and C20:1 species present in native GD1a (53.9% and 46.1%).(ABSTRACT TRUNCATED AT 250 WORDS)
Masserini
M
M
Department of Medical Chemistry and Biochemistry, Medical School, University of Milan, Italy.
Palestini
P
P
Venerando
B
B
Fiorilli
A
A
Acquotti
D
D
Tettamanti
G
G
D015060:1,2-Dipalmitoylphosphatidylcholine; D001665:Binding Sites; D002152:Calorimetry, Differential Scanning; D002462:Cell Membrane / Q000378:metabolism; D005732:Gangliosides / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes; D009439:Neuraminidase / Q000378:metabolism*; D013379:Substrate Specificity; D014734:Vibrio cholerae / Q000201:enzymology
D005732:Gangliosides; D008081:Liposomes; C021298:ganglioside, GD1a; D015060:1,2-Dipalmitoylphosphatidylcholine; D009439:Neuraminidase