Binding of pulmonary surfactant protein A to galactosylceramide and asialo-G M2

Abstract

The binding of pulmonary surfactant protein A (SP-A) to glycolipids was examined in the present study. The direct binding of SP-A on a thin-layer chromatogram was visualized using 125I-SP-A as a probe. 125I-SP-A bound to galactosylceramide and asialo-G M2, but failed to exhibit significant binding to G M1, G M2, asialo-G M1, sulfatide, and Forssman antigen. The study of 125I-SP-A binding to glycolipids coated onto microtitier wells also revealed that SP-A bound to galactosylceramide and asialo-G M2. SP-A bound to galactosylceramides with non-hydroxy or hydroxy fatty acids, but showed no binding to either glucosylceramide or galactosylsphingosine. Excess native SP-A competed with 125I-SP-A for the binding to asialo-G M2 and galactosylceramide. Specific antibody to rat SP-A inhibited 125I-SP-A binding to glycolipids. In spite of chelation of Ca 2+ with EDTA or EGTA, SP-A retained a significant binding to glycolipids. Inclusion of excess monosaccharides in the binding buffer reduced the glycolipid binding of SP-A, but failed to achieve complete abolishment. The oligosaccharide isolated from asialo-G M2 is also effective at reducing 125I-SP-A binding to the solid-phase asialo-G M2. From these data, we conclude that SP-A binds to galactosylceramide and asialo-G M2, and that both saccharide and ceramide moieties in the glycolipid molecule are important for the binding of SP-A to glycolipids.