2e1n
From Proteopedia
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Crystal structure of the Cyanobacterium circadian clock modifier Pex
Overview
Circadian clocks are self-sustained biochemical oscillators. The, oscillator of cyanobacteria comprises the products of three kai genes, (kaiA, kaiB, and kaiC). The autophosphorylation cycle of KaiC oscillates, robustly in the cell with a 24-h period and is essential for the basic, timing of the cyanobacterial circadian clock. Recently, period extender, (pex), mutants of which show a short period phenotype, was classified as a, resetting-related gene. In fact, pex mRNA and the pex protein (Pex), increase during the dark period, and a pex mutant subjected to diurnal, light-dark cycles shows a 3-h advance in rhythm phase. Here, we report the, x-ray crystallographic analysis and biochemical characterization of Pex, from cyanobacterium Synechococcus elongatus PCC 7942. The molecule has an, (alpha+beta) structure with a winged-helix motif and is indicated to, function as a dimer. The subunit arrangement in the dimer is unique and, has not been seen in other winged-helix proteins. Electrophoresis mobility, shift assay using a 25-base pair complementary oligonucleotide, incorporating the kaiA upstream sequence demonstrates that Pex has an, affinity for the double-stranded DNA. Furthermore, mutation analysis shows, that Pex uses the wing region to recognize the DNA. The in vivo rhythm, assay of Pex shows that the constitutive expression of the pex gene, harboring the mutation that fails to bind to DNA lacks the, period-prolongation activity in the pex-deficient Synechococcus, suggesting that Pex is a DNA-binding transcription factor.
About this Structure
2E1N is a Single protein structure of sequence from Synechococcus sp. with as ligand. Full crystallographic information is available from OCA.
Reference
Structural and biochemical characterization of a cyanobacterium circadian clock-modifier protein., Arita K, Hashimoto H, Igari K, Akaboshi M, Kutsuna S, Sato M, Shimizu T, J Biol Chem. 2007 Jan 12;282(2):1128-35. Epub 2006 Nov 10. PMID:17098741
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