Infrared studies of fully hydrated unsaturated phosphatidylserine bilayers. Effect of Li+ and Ca2+.
Infrared spectroscopy has been used to characterize the thermal-phase behavior of fully hydrated 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS) and 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS) as well as their interaction with Li+ and Ca2+. The order-disorder transition of POPS-NH4+ is at 17 degrees C; in the presence of Li+ a POPS-Li+ complex is formed, and the transition temperature of this complex is 40 degrees C. DOPS-NH4+ has an order-disorder transition at -11 degrees C, and unlike POPS the addition of Li+ has no effect on the thermal behavior of DOPS-NH4+. This indicates that the binding of Li+ to DOPS is negligible or very weak. Li+ binds to the phosphate and carboxylate groups of POPS, and as a result these groups lose their water of hydration. Li+ binding induces a conformational change, probably in the glycerol backbone of POPS; however, the conformation of the two P-O ester bonds remains gauche-gauche as in POPS-NH4+. Both POPS and DOPS form crystalline complexes with Ca2+. As a result of Ca2+ binding to the phosphate, this group loses its water of hydration and there is a conformational change in the P-O ester bonds from gauche-gauche to antiplanar-antiplanar. In contrast to the POPS-Li+ complex, the carboxylate group remains hydrated in the Ca2+ complexes. Furthermore, in these PS-Ca2+ complexes a new hydrogen bond is formed between one of the ester C=O groups and probably water. Such a situation is not found in the NH4+ and Li+ salts of phosphatidylserine.
Casal
H L
HL
Division of Chemistry, National Research Council of Canada, Ottawa.
Martin
A
A
Mantsch
H H
HH
Paltauf
F
F
Hauser
H
H
D002118:Calcium; D008051:Lipid Bilayers; D008094:Lithium; D008968:Molecular Conformation; D010718:Phosphatidylserines; D013055:Spectrophotometry, Infrared; D013329:Structure-Activity Relationship
D008051:Lipid Bilayers; D010718:Phosphatidylserines; D008094:Lithium; D002118:Calcium