Figure 1. Model of the TMD-mediated interactions of the NMDAR–ND2 complex.

(a) Human ND2 homology model. Lateral and cytoplasmic views of the ND2 in cartoon and surface representations. The outer surface of ND2 is almost featureless on all sides except for the presence of a deep TM groove surrounded by TM helices 1, 5, 8 and 11 TMs, shown in salmon colour. (b) Structural basis for the formation of the ND2 TM groove. Structural alignment of the human ND2 homology model (cyan and salmon, as in a) with E. coli. NuoN subunit from complex I (beige, PDB code: 3RKO) in cartoon and surface representations. The evolutionary switch from ‘long' to ‘short' ND2 with the emergence of bilateral metazoans causes the loss of three N-terminal helices. The absence of the third helix results in the formation of a deep groove in ‘short' ND2, including in the human ND2. See also Supplementary Figs 1 and 2.