1y28
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(New page: 200px<br /><applet load="1y28" size="450" color="white" frame="true" align="right" spinBox="true" caption="1y28, resolution 2.10Å" /> '''Crystal structure of...)
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Revision as of 04:23, 21 November 2007
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Crystal structure of the R220A metBJFIXL HEME domain
Overview
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.
About this Structure
1Y28 is a Single protein structure of sequence from Bradyrhizobium japonicum with HEM as ligand. Full crystallographic information is available from OCA.
Reference
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
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