1y28

Crystal structure of the R220A metBJFIXL HEME domain

spinqualitylabelsall models 1y28, resolution 2.10Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 1y28 is a 1 chain structure with sequence from Bradyrhizobium japonicum. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Method: X-ray diffraction, Resolution 2.1Å Ligands: HEM Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Function FIXL_BRADU Putative oxygen sensor; modulates the activity of FixJ, a transcriptional activator of nitrogen fixation fixK gene. FixL probably acts as a kinase that phosphorylates FixJ. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMed To evaluate the contributions of the G(beta)-2 arginine to signal transduction in oxygen-sensing heme-PAS domains, we replaced this residue with alanine in Bradyrhizobium japonicum FixL and examined the results on heme-domain structure, ligand binding, and kinase regulation. In the isolated R220A BjFixL heme-PAS domain, the iron-histidine bond was increased in length by 0.31 A, the heme flattened even without a ligand, and the interaction of a presumed regulatory loop (the FG loop) with the helix of heme attachment was weakened. Binding of carbon monoxide was similar for ferrous BjFixL and R220A BjFixL. In contrast, the level of binding of oxygen was dramatically lower (K(d) approximately 1.5 mM) for R220A BjFixL, and this was manifested as 60- and 3-fold lower on- and off-rate constants, respectively. Binding of cyanide followed the same pattern as binding of oxygen. The catalytic activity was 3-4-fold higher in the "on-state" unliganded forms of R220A BjFixL than in the corresponding BjFixL species. Cyanide regulation of this activity was strongly impaired, but some inhibition was nevertheless preserved. Carbon monoxide and nitric oxide regulation, although weak in BjFixL, were abolished from R220A BjFixL. We conclude that the G(beta)-2 arginine assists in the binding of oxygen to BjFixL but does not accomplish this by stabilizing the oxy form. This arginine is not absolutely required for regulation, although it is important for shifting a pre-existing kinase equilibrium toward the inactive state on binding of regulatory ligands. These findings support a regulatory model in which the heme-PAS domain operates as an ensemble that couples to the kinase rather than a mechanism driven by a single central switch. A distal arginine in oxygen-sensing heme-PAS domains is essential to ligand binding, signal transduction, and structure.,Dunham CM, Dioum EM, Tuckerman JR, Gonzalez G, Scott WG, Gilles-Gonzalez MA Biochemistry. 2003 Jul 1;42(25):7701-8. PMID:12820879 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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