Hydrophobicity causes anomalous migration of cystine/glutamate antiporter SLC7A11 in SDS-PAGE with low acrylamide concentration

The cystine/glutamate antiporter, solute carrier family 7 member 11 (SLC7A11), plays a crucial role in regulating redox homeostasis and cell death processes such as apoptosis and ferroptosis. These processes are implicated in various diseases, including cancer, organ injuries and neurodegenerative disorders. However, the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) expression pattern of SLC7A11 varies across studies and remains unclear. In many studies, including ours, SLC7A11 migrates at an atypical molecular weight (MW) of approximately 37 kDa, which is lower than its theoretical molecular mass of 55.4 kDa. This discrepancy raises concerns about the precise molecular mass and expression pattern of SLC7A11 in SDS-PAGE. We confirmed that this fast-migrating band corresponds to SLC7A11 through knockdown of endogenous SLC7A11 or overexpression of exogenous SLC7A11. Furthermore, we ruled out the possibility of proteolytic cleavage after protein translation. We found that the high hydrophobicity of SLC7A11 is a key factor responsible for its anomalous migration. Substituting the non-polar residue isoleucine (Ile) with the polar residue asparagine (Asn) reduced its hydrophobicity and restored normal migration, aligning with its predicted MW of 55 kDa. Additionally, we observed that SLC7A11 migrated faster in SDS-PAGE at lower acrylamide concentrations, whereas higher concentrations (e.g. 12% or 15%) eliminated the gel shift. This study clarifies the expression pattern of SLC7A11 in SDS-PAGE and emphasizes the importance of considering physicochemical properties such as hydrophobicity and gel concentration when characterizing membrane proteins like SLC7A11.