2o9c

From Proteopedia

Revision as of 13:19, 23 January 2008

Crystal Structure of Bacteriophytochrome chromophore binding domain at 1.45 angstrom resolution

Overview

Phytochromes are red/far red light photochromic photoreceptors that direct, many photosensory behaviors in the bacterial, fungal, and plant kingdoms., They consist of an N-terminal domain that covalently binds a bilin, chromophore and a C-terminal region that transmits the light signal, often, through a histidine kinase relay. Using x-ray crystallography, we recently, solved the first three-dimensional structure of a phytochrome, using the, chromophore-binding domain of Deinococcus radiodurans bacterial, phytochrome assembled with its chromophore, biliverdin IXalpha. Now, by, engineering the crystallization interface, we have achieved a, significantly higher resolution model. This 1.45A resolution structure, helps identify an extensive buried surface between crystal symmetry mates, that may promote dimerization in vivo. It also reveals that upon ligation, of the C3(2) carbon of biliverdin to Cys(24), the chromophore A-ring, assumes a chiral center at C2, thus becoming 2(R),3(E)-phytochromobilin, a, chemistry more similar to that proposed for the attached chromophores of, cyanobacterial and plant phytochromes than previously appreciated. The, evolution of bacterial phytochromes to those found in cyanobacteria and, higher plants must have involved greater fitness using more reduced, bilins, such as phycocyanobilin, combined with a switch of the attachment, site from a cysteine near the N terminus to one conserved within the cGMP, phosphodiesterase/adenyl cyclase/FhlA domain. From analysis of, site-directed mutants in the D. radiodurans phytochrome, we show that this, bilin preference was partially driven by the change in binding site, which, ultimately may have helped photosynthetic organisms optimize shade, detection. Collectively, these three-dimensional structural results better, clarify bilin/protein interactions and help explain how higher plant, phytochromes evolved from prokaryotic progenitors.

About this Structure

2O9C is a Single protein structure of sequence from Deinococcus radiodurans with as ligand. Active as Histidine kinase, with EC number 2.7.13.3 Full crystallographic information is available from OCA.

Reference

High resolution structure of deinococcus bacteriophytochrome yields new insights into phytochrome architecture and evolution., Wagner JR, Zhang J, Brunzelle JS, Vierstra RD, Forest KT, J Biol Chem. 2007 Apr 20;282(16):12298-309. Epub 2007 Feb 23. PMID:17322301

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