Fig. 3.

Sequence and transmembrane organization of the MFSD2 receptor. (A) Primary sequence of the 530 amino acid-long human MFSD2 protein, with the 10 membrane-spanning domains predicted by the TMHMM program indicated in gray on the sequence, together with the schematic structure of the protein. (B) Immunofluorescence analysis of the human (hMFSD2-HA) or murine (mMFSD2-HA) C-terminally HA-tagged MFSD2 proteins using as a control the untagged hMFSD2 protein. The tagged proteins were verified to be still functional in a pseudotype assay as in Fig. 2 (data not shown). HeLa cells transduced with the corresponding expression vector were either fixed, permeabilized and stained with an anti-HA antibody (whole-cell staining, “perm”) or observed directly after staining without prior fixation or permeabilization (cell surface staining, “nonperm”). Observations were made with confocal microscopy by using a FITC-conjugated secondary antibody which demonstrated cell surface localization of the human and murine MFSD2 proteins with the HA-tag only accessible after membrane permeabilization.