2cmn | pdb_00002cmn
A Proximal Arginine Residue in the Switching Mechanism of the FixL Oxygen Sensor
Structural highlights
FunctionFIXL_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 PubMedIn oxygen-sensing PAS domains, a conserved polar residue on the proximal side of the heme cofactor, usually arginine or histidine, interacts alternately with the protein in the "on-state" or the heme edge in the "off-state" but does not contact the bound ligand directly. We assessed the contributions of this residue in Bradyrhizobium japonicum FixL by determining the effects of an R206A substitution on the heme-PAS structure, ligand affinity, and regulatory capacity. The crystal structures of the unliganded forms of the R206A and wild-type BjFixL heme-PAS domains were similar, except for a more ruffled porphyrin ring in R206A BjFixL and a relaxation of the H214 residue and heme propionate 7 due to their lost interactions. The oxygen affinity of R206A BjFixL (Kd approximately 350 microM) was 2.5 times lower than that of BjFixL, and this was due to a higher off-rate constant for the R206A variant. The enzymatic activities of the unliganded "on-state" forms, either deoxy or met-R206A BjFixL, were comparable to each other and slightly lower (twofold less) than those of the corresponding BjFixL species. The most striking difference between the two proteins was in the enzymatic activities of the liganded "off-state" forms. In particular, saturation with a regulatory ligand (the Fe(III) form with cyanide) caused a >2000-fold inhibition of the BjFixL phosphorylation of BjFixJ, but a 140-fold inhibition of this catalytic activity in R206A BjFixL. Thus, in oxygen-sensing PAS domains, the interactions of polar residues with the heme edge couple the heme-binding domain to a transmitter during signal transduction. A proximal arginine R206 participates in switching of the Bradyrhizobium japonicum FixL oxygen sensor.,Gilles-Gonzalez MA, Caceres AI, Sousa EH, Tomchick DR, Brautigam C, Gonzalez C, Machius M J Mol Biol. 2006 Jun 30;360(1):80-9. Epub 2006 May 11. PMID:16813836[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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