Spectrin involvement in a 40°C structural transition of the red blood cell membrane

Abstract

Proteins involved in a structural transition detected in red blood cell membranes at 40°C by spin labeling methods have been investigated. Antibodies specific for spectrin, band 3, and protein 4.1 have been used as specific probes to modify membrane thermotropic properties. Spectrin seems to be involved in a 40°C transition detected in ghosts by both a stearic acid spin label (16-doxyl stearic) and a sulfhydryl-specific maleimide analogue spin label. Circular dichroism and maleimide spin labeling studies of purified spectrin show a slow unfolding of the protein structure starting at 25-30°C and a massive transition with an onset temperature of 48 and 40°C, respectively. This thermotropic behavior of spectrin could be the process that modifies membrane physicochemical properties above 40°C that are detected by the stearic acid spin label. The transition detected by the stearic acid spin label was modified both by antispectrin antibodies and anti-4.1 protein antibodies, but not by antibodies specific for the cytoplasmic domain of band 3. These results suggest an involvement of protein 4.1 in regulating spectrin unfolding at the membrane level. A selective inhibition of the transition detected by the maleimide spin label has been obtained with a monoclonal antispectrin antibody at 1 : 1 molar ratio. The involvement in this transition of a localised spectrin domain(s) containing few exposed sulfhydryl groups is proposed.