ExuR is capable of binding to the uxuR promoter in the presence of glucuronate, unlike UxuR, which can bind to its own promoter in the absence of glucuronate. However, the induction of uxuR in the presence of glucuronate is dependent on exuR, as demonstrated with an exuR mutant strain that lost the capability of induction of uxuR expression by glucuronate [2] UxuR is a protein that belongs to the GntR family and participates as a regulator of several genes involved in carbon uptake. When glucuronate is present, transcription derepression by UxuR is induced [16]; however, it was demonstrated that this effect is induced specifically by action of D-fructuronate and not by its precursor, D-glucuronate, since in a uxaC knockout strain (uxaC encodes the uronate isomerase), derepression was not observed when glucuronate was added [16]. Using homology modeling, the quaternary structure of ExuR has been proposed [16]. It is a homodimer of two domains connected by a linker region which is highly flexible, allowing fast and large movements of the N-terminal domains [16]. Based on molecular dynamics analysis, it was predicted that when the D-fructuronate is bound, UxuR has a conformation with a more pronounced negative charge at the surface of the DNA-binding regions, while in its absence, UxuR adopts a conformation with a more positive character at the surface of this region [16]. UxuR has a putative zinc-binding motif at the C-terminal region composed of three histidine residues (H152, H201, and H223) and one aspartate (D148), which were identified by homology modeling and molecular docking [16]. Individual mutations in UxuR (H152A, H201A, and D148A) prevent expression derepression induced by D-fructuronate [16].