The 3D structure formed MSD1-NBD1-MSD2-NBD2 as a common structural fold of ABC transporters (Fig. 2a). MSD1 and MSD2 were made up of TM1–6 and TM7–12, respectively (Fig. 2b). When CsMRP4 was compared structurally with the 38 homologs from PDB entries using ENDscript  with strict parameters, two NBDs were found to be highly conserved and two MSDs were less conserved (Fig. 2c). Furthermore, NBD2 of CsMRP4 was significantly more conserved than NBD1. At the sequence level, even though CsMRP4 was compared with five short forms of the ABCC subfamily, NBD2 contained 56 identical residues but NBD1 had only 41 identical residues (Fig. 3a, b). These results corroborate previous findings showing that NBD2 of CsMRP7 is more conserved than NBD1 at the structural level .Fig. 3Comparison of the amino acid sequence of CsMRP4 with short forms of the ABCC subfamily. CsMRP4 was aligned with HsMRP4, 5, 8, 9, and CFTR using MAFFT and rendered using ESPript. Out of the alignment profile, the NBD1 region (a) and NBD2 region (b) were selected for visualization. Red bold and red letters indicate identical and similar amino acid residues, respectively. Conserved sequences are indicated by a box if more than 70% of the residues are similar