Structural and biochemical characterization of circadian clock related protein Pex in Synechococcus elongatus PCC 7942

Abstract

The Pex protein in cyanobacterium Synechococcus elongatus PCC 7942 fine-tunes the period and the phase of the circadian clock. We carried out X-ray crystal structure analysis of Pex. We prepared the Pex lacking the 14 residues and obtained good crystal of the protein. Then we determined the crystal structure at 1.8 angstrom in resolution. As a result, we revealed that Pex had a winged-helix structure, which was a typical DNA binding motif. By DNA gel shit assay, binding of Pex to a DNA fragment of kaiA promoter region was confirmed. While the arginine residue at 106th in the protein was estimated as an important portion to contact DNA, its substitution to alanine diminished the binding activity. We also established the Synechococcus cell constitutively expressing the mutant Pex, and examined the clock by bioluminescence monitoring. Then, no activity of the period lengthening was observed.