Stereo view of a 3D model of the ERMAP immunoglobulin domain and a schematic representation of the protein topology.

The 2 amino acid positions that are involved in the Sc1/Sc2 and Rd polymorphism are colored. In the wild-type ERMAP expressing Sc1 but lacking Rd antigens, there is a Gly (red) at position 57 and a Pro (green) at position 60 (A). The Sc2 antigen is caused by an Arg (blue) at position 57 (B), the Rd antigen by an Ala (light blue) at position 60 (C). The topology of the ERMAP protein as predicted by Su et al23 is shown (D). The mature protein starts at amino acid position 30. The aminotermial protein segment up to amino acid 157 is located extracellularly. The immunoglobulin V domain (amino acids 50-126) and a few adjacent amino acids (heavy line, amino acids 46-131) is modeled as shown in panels A to C. Almost two thirds of the protein (amino acids 177-475) are predicted to be located intracellularly and encompass a B30.2 domain.