OLIGOMERIC NATURE OF THE INTEGRAL MEMBRANE-PROTEIN STOMATIN

The 32-kDa integral membrane protein stomatin (protein 7.2b) is not on ly an important component of the red cell membrane but can also be fou nd in abundance in different tissues and cell lines. The protein is th ought to be anchored to the membrane by a hydrophobic domain while bot h N and C termini are exposed to the cytoplasm. We have previously sho wn in the human cell line UAC that stomatin concentrates preferentiall y in plasma membrane folds and protrusions. There is also evidence tha t stomatin is linked to the cortical actin cytoskeleton, suggesting a role in cortical morphogenesis of the cell. In this study, we demonstr ate that the fundamental structure of stomatin is oligomeric, Whereas interaction of stomatin with itself was suggested by cross-linking exp eriments, we show by density gradient centrifugation analysis that sol uble homo-oligomeric complexes of this protein are present in Triton X -100 extracts of UAC cells. We also show the existence of these oligom ers by co-immunoprecipitation of the endogenous stomatin and a recombi nantly expressed myc-tagged stomatin, using an anti-myc antibody. The data indicate that these complexes comprise between 9 and 12 monomers of stomatin, Two C-terminally truncated forms of stomatin do not incor porate into these oligomers, suggesting an involvement of the C termin us in the homo-oligomeric interaction.