Figure 2: Primary structure of 4.1R isoforms and mapping of known binding partners for 4.1R. A) Translation of the prototypical red blood cell 80 kDa 4.1R isoform (4.1R80) is initiated at AUG-2, which is located in exon 4. Translation of the 135 kDa 4.1R isoform (4.1R135), an isoform expressed in early erythroblasts and other nucleated cells, is initiated at AUG-1, which is located in exon 2’ (ID: P11171). The 30 kDa membrane binding domain is the so-called “FERM” domain. An updated list of the binding partners identified for each domain of 4.1R is displayed. CPAP refers to a “centrosomal protein 4.1R-associated protein”, reported by Hung et al. [86]. B) Schematic representation of 4.1R80 and CaM are shown. 4.1R80 contains a R30 (FERM domain), which is located at the N-terminal end and a spectrin and actin binding (SAB) domain. Amino terminal and carboxy terminal ends are represented as N and C.A 3D representation of the 30 kDa FERM domain of 4.1R, visualized with the MolFeat® software (version 4.6), is displayed (PDB accession No. 1GG3). The 30 kDa domain consists of three lobes (N-, α- and C-lobe), and adopts a threeleaf clover shape [31].