Alignment of the human MCTs with highlighted positions of pathogenic mutations reported for MCT8. This alignment compares the human MCT sequences and in addition MCT8 of rat and mice (MCT8 are red boxed). Conserved residues are marked by different colours according to their biophysical properties (blue - positively charged, red - negatively charged, green/orange - hydrophobic, gray - hydrophilic, black – proline, cyan - aromatic). Black boxed are the potential dimensions of the transmembrane helices (TMHs) based on the X-ray structure of the E.coli Glycerol-3-phosphate transporter, another member of the major facilitator superfamily which was used as a structural template to build the MCT8 homology model. Red stars above the hMCT8 sequence indicating positions where naturally occurring mutations for the hMCT8 are reported. Few of them are at positions with a high degree of conservation like R445 (R8.50). In addition, the positively charged residues and histidines hypothesized in this study as to be potentially involved in substrate transport (figure 7) are annotated above the sequences in blue. For each helix the most highly conserved residue is numbered according to a unifying numbering system (see Material and Methods).