Fig. 5: The GsAcuB contains adenine nucleotide binding sites as described for BsAcuB.
From: AcuB senses cellular energy charge to coordinate acetyl-CoA synthesis in bacteria
a Crystal structure of nucleotide free GsAcuB shows formation of a scissor-shaped dimer (PDB: 9SAW). A monomer consists of an N-terminal Bateman domain encompassing two CBS-modules and a C-terminal ACT domain (C: ACT domain). Each Bateman domain contains two adenine nucleotide binding sites, which are empty. In the ACT domain dimer two round-shaped positive electron densities lining the interface of α1-α1’. Two chloride ions (or alternatively four water molecules) were placed there. The figure was created with PyMOL88. b The GsAcuB dimer contains two positively-charged surface-exposed cavities binding to adenine nucleotides as shown here for the structure of GsAcuB in complex with four molecules of AMP (PDB: 9S52). As shown for BsAcuB the adenosine moieties of the nucleotides are surface exposed while the phosphate groups point towards the interior of the Bateman domains. The electrostatics was calculated with the APBS Electrostatics Plugin in PyMOL81,88. The figure was created with PyMOL88. c Two types of adenine nucleotide binding sites can be distinguished in each monomer in GsAcuB as shown for BsAcuB. As representative the closeup shows the ADP binding sites for the structure of GsAcuB solved in complex with four molecules of ADP (PDB: 9SAX). The type I and type II adenine nucleotide binding sites provide a specific setup or residues for binding the adenine base, the ribose and the phosphate moieties. His35 forms a bridge by binding the α-phosphates of the adenine nucleotides binding on both sites of the AcuB monomer within the dimer. In the type I binding sites the of the dimer the β-phosphates of the bound ADP molecules interact with the side chains of Thr120 and Thr122 and of Arg34. Arg34 also binds the β-phosphate of the ADP molecule bound in the type II site. The specificity towards adenine nucleotides is determined by interactions with the exocyclic amino group at C6 and N1 of the adenine base (type I: main chain of Ile13, His35; type II: main chain of Cys106 and Ile84). The figure was created with PyMOL88.
