NAC domain superfamily

The NAC domain (for Petunia hybrida (Petunia) NAM and for Arabidopsis ATAF1, ATAF2, and CUC2) is an N-terminal module of ~160 amino acids, which is found in proteins of the NAC family of plant-specific transcriptional regulators (no apical meristem (NAM) proteins) [9212461]. NAC proteins are involved in developmental processes, including formation of the shoot apical meristem, floral organs and lateral shoots, as well as in plant hormonal control and defence. The NAC domain is accompanied by diverse C-terminal transcriptional activation domains. The NAC domain has been shown to be a DNA-binding domain (DBD) and a dimerization domain [11114891,12175016].

The NAC domain can be subdivided into five subdomains (A-E). Each subdomain is distinguishable by blocks of heterogeneous amino acids or gaps. While the NAC domains were rich in basic amino acids (R, K and H) as a whole, the distribution of positive and negative amino acids in each subdomain were unequal. Subdomains C and D are rich in basic amino acids but poor in acidic amino acids, while subdomain B contains a high proportion of acidic amino acids. Putative nuclear localization signals (NLS) have been detected in subdomains C and D [10660065]. The DBD is contained within a 60 amino acid region located within subdomains D and E [12175016]. The overall structure of the NAC domain monomer consists of a very twisted antiparallel beta-sheet, which packs against an N-terminal alpha-helix on one side and one shorter helix on the other side surrounded by a few helical elements. The structure suggests that the NAC domain mediates dimerization through conserved interactions including a salt bridge, and DNA binding through the NAC dimer face rich in positive charges [15083810].