Oligomeric Nature of the Integral Membrane Protein Stomatin

Abstract

The 31-kDa integral membrane protein stomatin (protein 7.2b) is not only an important component of the red cell membrane but can also be found in abundance in different tissues and cell lines. The protein is thought to be anchored to the membrane by a hydrophobic domain while both N and C termini are exposed to the cytoplasm. We have previously shown in the human cell line UAC that stomatin concentrates preferentially in plasma membrane folds and protrusions. There is also evidence that stomatin is linked to the cortical actin cytoskeleton, suggesting a role in cortical morphogenesis of the cell. In this study, we demonstrate that the fundamental structure of stomatin is oligomeric. Whereas interaction of stomatin with itself was suggested by cross-linking experiments, we show by density gradient centrifugation analysis that soluble homo-oligomeric complexes of this protein are present in Triton X-100 extracts of UAC cells. We also show the existence of these oligomers by co-immunoprecipitation of the endogenous stomatin and a recombinantly expressed myctagged 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 incorporate into these oligomers, suggesting an involvement of the C terminus in the homo-oligomeric interaction.

Ancient origin of reggie (flotillin), reggie-like, and other lipid-raft proteins: convergent evolution of the SPFH domain

“…In the absence of definitive phylogenetic criteria to support these relationships, we analyzed each group separately. The most representative SPFH superfamily protein, stomatin (also known as band 7.2b protein), is a major integral plasma membrane protein of human erythrocytes [41]. It is about 141 aa residues shorter than reggies/ flotillins and contains a hydrophilic N-terminal stretch (positions 1-31), followed by a hydrophobic transmembrane domain (postions 32-51), and the SPFH domain, which spans about 55% of the polypeptide (human positions 52-211; fig.…”

Mutation-dependent recessive inheritance of NPHS2-associated steroid-resistant nephrotic syndrome

“…On the basis of its predicted structure, podocin belongs to the stomatin protein family, with a hairpin-like intramembrane loop and intracellular N and C termini. The C-terminal portions of both stomatin and podocin are responsible for dimerization 6,[8][9][10][11][12] .…”

“…On the basis of its predicted structure, podocin belongs to the stomatin protein family, with a hairpin-like intramembrane loop and intracellular N and C termini. The C-terminal portions of both stomatin and podocin are responsible for dimerization 6,[8][9][10][11][12] .Individuals with NPHS2 mutations typically develop SRNS before 6 years of age and progress to ESRD during their first decade of life6. The phenotype can be less severe in the setting of a trans association of an NPHS2 mutation and the polymorphism c.686G>A (p.Arg229Gln, rs61747728), a genotype we hereafter denote as p.…”

Podocyte Biology and Response to Injury

“…Podocin is encoced by the NPHS2 gene, which is mutated in autosomal recessive, steroid-resistant nephrotic syndrome (62). Stomatin is present as high-order oligomers in erythrocyte lipid rafts, where it has a scaffolding function (83). Podocin localizes to the SD (16,21), accumulates there in an oligomeric form in lipid rafts and associates via its C-terminus with CD2AP and nephrin (16).…”