Mixed monolayer of dipalmitoylphosphatidylcholine and stage-specific embryonic antigen-1 (SSEA-1)

The mixing behavior of dipalmitoylphosphatidylcholine (DPPC) and stage-specific embryonic antigen-1 (SSEA-1) in air/water interface monolayer was estimated by measuring the surface pressure. For comparison, a DPPC and synthetic maltohexaosyl lipid (Mal6(C12)2) mixed monolayer was also measured. The DPPC–SSEA-1 system exhibits expanded–condensed phase transition. A thermodynamic analysis revealed that the DPPC–SSEA-1 system exhibits a negative azeotropic phase transition. This result indicates an attractive interaction between DPPC and SSEA-1, whereas SSEA-1 molecules show little specific interaction between themselves. Evaluation of the partial molecular area suggests the attractive interaction due to the steric effect of packing. Even on enough divalent salt solution, there is little change in the π–A curve. The attractive interaction between the SSEA-1 molecules requires a suitable arrangement of LeX determinant (Gal1 → 4[Fucα1 → 3]GlcNAcβ1 → R).