Structure of the conserved domain of ANAC, a member of the NAC family of transcription factors

Abstract

The structure of the DNA-binding NAC domain of Arabidopsis ANAC (abscisic-acid-responsive NAC) has been determined by Xray crystallography to 1.9 Å resolution (Protein Data Bank codes 1UT4 and 1UT7). This is the first structure determined for a member of the NAC family of plant-specific transcriptional regulators. NAC proteins are characterized by their conserved N-terminal NAC domains that can bind both DNA and other proteins. 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 does not possess a classical helix-turnhelix motif; instead it reveals a new transcription factor fold consisting of a twisted b-sheet surrounded by a few helical elements. The functional dimer formed by the NAC domain was identified in the structure, which will serve as a structural template for understanding NAC protein function at the molecular level.

A structural view of the conserved domain of rice stress-responsive NAC1

“…Subsequently, the results of ethylene glycol disuccinate di(Nsuccinimidyl) ester (EGS) cross-linking confirmed this observation and demonstrated that such a dimeric architecture does not dissociate, even at very high salt concentrations (5 M NaCl). These results indicate that the dimeric form should form the functional unit of the SNAC1 NAC domain, which is consistent with the previously reported results on the ANAC NAC domain (Ernst et al, 2004) and our knowledge that the dimerization of DNA binding domains is common and can function in modulating the DNA binding specificity (Müller, 2001). In the crystal structure, two molecules of the SNAC1 NAC domain, which are related by a crystallographic twofold axis, form a butterfly shaped homodimer (Fig.…”

“…The crystal structure of the conserved NAC domain of stressresponsive NAC1 (SNAC1) (residues Met1-Lys174) was determined by the molecular replacement (MR) method using the crystal structure of the NAC domain of ANAC (PDB code: 1UT4) (Ernst et al, 2004) as the initial searching model. The final structure was refined to 2.5 Å resolution with a final R work value of 23.1% (R free = 26.7%).…”

“…As SNAC1 NAC has a longer amino acid sequence in this region, we speculate that this region could be crucial for the biologic role of the SNAC1 NAC domain, which might be different from the ANAC NAC domain. Nonetheless, according to the high amino acid sequence similarity (60%) with ANAC, the central part of the SNAC1 NAC domain unexpectedly shares a high topological similarity with the structure of ANAC (PDB code: 1UT4) (Ernst et al, 2004) as well. However, distinct structural differences are observed between these two structures.…”

“…However, distinct structural differences are observed between these two structures. First, the N-terminal extended residues in the structure of ANAC NAC domain are involved in contacts with symmetric molecule and thus have relative good agreement (Ernst et al, 2004). In contrast, although there are several residues that remain in the N-terminus of the SNAC1 NAC domain caused by the expression vector, all of these residues are totally unobserved in the crystal structure of SNAC1 NAC domain suggesting a high flexibility.…”

“…Although NAC family transcription factors play key roles in plant, limited knowledge of their detailed structures or DNA binding mechanism is known and only one crystal structure of NAC family protein has been previously reported (Ernst et al, 2004). To gain a better understanding of the structural details of NAC family transcription factors, here we describe the crystal structure of the SNAC1 NAC domain and show that the overall architecture adopts a conserved NAC family fold.…”