Heat Shock Protein 90 Recognized as an Iron-Binding Protein Associated with the Plasma Membrane of HeLa Cells

Heat shock protein 90 (Hsp90) is a molecular chaperone abundant in eukaryotic cells. However, its exact role is not completely understood yet. Employing an iron-binding assay and mass spectrometric analysis, we have identified human Hsp90 as an iron-binding protein in membrane protein preparations of human HeLa cells. Western blot analysis and confocal microscopy confirmed that a portion of cellular Hsp90 is associated with the plasma membrane, but it does not seem to be expressed on the cell surface. The iron-binding assay with purified human Hsp90 confirmed iron binding by Hsp90. Thus we suggest that Hsp90 is an iron-binding protein associated with the plasma membrane.