1XJ2: Co-Bound Structure Of Bjfixlh

Rhizobia directly regulate the expression of genes required for symbiotic nitrogen fixation in response to oxygen concentration via the sensor protein FixL. The N-terminal PAS domain of FixL contains a histidine-coordinated heme and regulates the activity of its effector domain, a C-terminal histidine kinase, in response to binding of oxygen and other ligands at the heme. To further investigate ligand-induced inhibition of FixL, we have determined the crystal structures of the heme domain in both the deoxy state and bound to carbon monoxide, a weak inhibitor of FixL kinase activity. Structures collected at room temperature are presented in each state from two crystallographic space groups at 1.8 and 2 A resolution. These structures reveal displacement of the residues of the H(beta) and I(beta) strands by Leu236 upon CO binding, and this structural change propagates more than 15 A to a region of the structure implicated in signal transduction in PAS proteins. Displacement of residues Ile215, Ile216, and Gly217 in the FG loop is also evident, accompanied by the movement of heme propionate 6 upon change in iron ligation. CO binding increases the temperature factors in the FG loop of the protein and disorders the side chain of Arg206, a conserved residue involved in the FG loop switch mechanism. We relate these results to structural changes in other PAS sensor domains and their involvement in catalytic control.
PDB ID: 1XJ2Download
MMDB ID: 32423
PDB Deposition Date: 2004/9/22
Updated in MMDB: 2012/10
Experimental Method:
x-ray diffraction
Resolution: 2  Å
Source Organism:
Similar Structures:
Biological Unit for 1XJ2: monomeric; determined by author
Molecular Components in 1XJ2
Label Count Molecule
Protein (1 molecule)
Sensor Protein Fixl(Gene symbol: fixL)
Molecule annotation
Chemicals (2 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB