Locating the Band III protein in quasi-native cell membranes

Band III is a key protein for the structure and function of red blood cell membranes. To date, the distribution and morphology of Band III in cell membranes is still unclear because of limited approaches. We applied Topography and RECognition imaging microscopy (TREC), which extends the application of atomic force microscopy (AFM) to recognize a single molecule in a biological complex, to visually locate a single Band III protein in quasi-native cell membranes by anti-Band III-functionalized AFM tips under physiological conditions. The Band III proteins are well distributed in the inner leaflet of cell membranes. The height of the whole Band III protein in cell membranes is in the range of 9-13 nm. The unbinding force between Band III in the membrane and anti-Band III on the AFM tip is about 70 pN with the loading rate at 40 nN/s. Our result is significant in revealing the location and morphology of Band III in the inner cell membrane at the molecular level.