PDBsum entry 2b4m

Transport protein

PDB id: 2b4m

Contents

Protein chains

264 a.a. *

Ligands

PBE ×2

* Residue conservation analysis

PDB id:

2b4m

Name:

Transport protein

Title:

Crystal structure of the binding protein opuac in complex with proline betaine

Structure:

Glycine betaine-binding protein. Chain: a, b. Engineered: yes

Source:

Bacillus subtilis. Organism_taxid: 1423. Gene: opuac. Expressed in: escherichia coli bl21(de3). Expression_system_taxid: 469008.

Resolution:

2.80Å R-factor: 0.231 R-free: 0.283

Authors:

C.Horn,L.Sohn-Boesser,J.Breed,W.Welte,L.Schmitt,E.Bremer

Key ref:

C.Horn et al. (2006). Molecular determinants for substrate specificity of the ligand-binding protein OpuAC from Bacillus subtilis for the compatible solutes glycine betaine and proline betaine. J Mol Biol, 357, 592-606. PubMed id: 16445940 DOI: 10.1016/j.jmb.2005.12.085

Date:

26-Sep-05 Release date: 21-Mar-06

Protein chains

P46922  (OPUAC_BACSU) -  Glycine betaine-binding protein OpuAC from Bacillus subtilis (strain 168)

Seq: 293 a.a.

Struc: 264 a.a.

Enzyme reactions

• Enzyme class: E.C.?

DOI no: 10.1016/j.jmb.2005.12.085

J Mol Biol 357:592-606 (2006)

PubMed id: 16445940

Molecular determinants for substrate specificity of the ligand-binding protein OpuAC from Bacillus subtilis for the compatible solutes glycine betaine and proline betaine.

C.Horn, L.Sohn-Bösser, J.Breed, W.Welte, L.Schmitt, E.Bremer.

ABSTRACT

Compatible solutes play a decisive role in the defense of microorganisms against changes in temperature and increases in osmolarity in their natural habitats. In Bacillus subtilis, the substrate-binding protein (SBP)-dependent ABC-transporter OpuA serves for the uptake of the compatible solutes glycine betaine (GB) and proline betaine (PB). Here, we report the determinants of compatible solute binding by OpuAC, the SBP of the OpuA transporter, by equilibrium binding studies and X-ray crystallography. The affinity of OpuAC/GB and OpuAC/PB complexes were analyzed by intrinsic tryptophan fluorescence and the K(D) values were determined to be 17(+/-1)microM for GB and 295(+/-27)microM for PB, respectively. The structures of OpuAC in complex with GB or PB were solved at 2.0 A and 2.8 A, respectively, and show an SBP-typical class II fold. The ligand-binding pocket is formed by three tryptophan residues arranged in a prism-like geometry suitable to coordinate the positive charge of the trimethyl ammonium group of GB and the dimethyl ammonium group of PB by cation-pi interactions and by hydrogen bonds with the carboxylate moiety of the ligand. Structural differences between the OpuAC/GB and OpuAC/PB complexes occur within the ligand-binding pocket as well as across the domain-domain interface. These differences provide a structural framework to explain the drastic differences in affinity of the OpuAC/GB and OpuAC/PB complexes. A sequence comparison with putative SBP specific for compatible solutes reveals the presence of three distinct families for which the crystal structure of OpuAC might serve as a suitable template to predict the structures of these putative compatible solute-binding proteins.

Selected figure(s)

Figure 2.
Figure 2. Overall structure of the OpuAC/GB complex. Domain 1 (residues 1-96 and 251-272) and domain 2 (residues 97-250) are colored light magenta and red. N and C termini are labeled at the bottom. The ligand, which is coordinated by three Trp residues colored yellow, is shown in ball-and-stick representation. The inset shows the topology of OpuAC.

Figure 3.
Figure 3. Stereo view of the ligand-binding pocket of OpuAC. (a) Coordination of GB and (b) coordination of PB. Interactions between the ligands, GB and PB respectively, are highlighted by broken green lines. For a Figure including a 1F[o] -F[c] omit map, please see Supplementary Data Figure S1.

The above figures are reprinted by permission from Elsevier: J Mol Biol (2006, 357, 592-606) copyright 2006.

Figures were selected by the author.