title: Heme-binding characteristics of the isolated PAS-B domain of mouse Per2, a transcriptional regulatory factor associated with circadian rhythms.
abstract: Mouse period homolog 2 (mPer2), an important transcriptional regulatory factor associated with circadian rhythms, is composed of two N-terminal PAS (PAS-A and PAS-B) domains and a C-terminal domain. The PAS-A domain of mPer2 binds the heme iron via a Cys axial ligand. A corresponding transcriptional regulatory factor, neuronal PAS 2 protein (NPAS2), also contains PAS-A and PAS-B domains at the N-terminus with heme-binding capability. In particular, the PAS-B domain appears important for protein-protein interactions critical for transcriptional regulation. In the present study, we examined the heme-binding characteristics of the isolated PAS-B domain of mPer2. Our experiments show that the Fe(III) heme binds the isolated PAS-B domain with a heme to protein stoichiometry of 1:1. The Fe(III) protein complex is suggested to consist of an admixture of 6-coordinated His-bound high-spin and low-spin complexes. Marked pH-dependent spectral changes were observed, in contrast to the spectrum of the Fe(III) bound PAS-A domain of mPer2, which appeared pH-resistant. Treatment with diethylpyrocarbonate abolished the heme-binding ability of this protein, supporting the proposal that His is the axial ligand. Heme dissociation was composed of two phases with rate constants of 4.3 × 10⁻⁴ s⁻¹ (50%) and 4.0 × 10⁻³ s⁻¹ (50%), which were markedly higher than that (1.5 × 10⁻⁷ s⁻¹) of the prototype heme protein, myoglobin. The Soret CD band of the H454A PAS-B mutant was significantly different from those of wild-type and other His mutant proteins, strongly suggesting that His454 is one of the axial ligands for the Fe(III) complex.
authors.affiliation: Institute of Multidisciplinary Research for advanced Materials, Tohoku University, Sendai, Japan.
authors.forename: Koya
authors.initials: K
authors.lastname: Hayasaka
authors.forename: Kenichi
authors.initials: K
authors.lastname: Kitanishi
authors.forename: Jotaro
authors.initials: J
authors.lastname: Igarashi
authors.forename: Toru
authors.initials: T
authors.lastname: Shimizu
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001483:Base Sequence; D002940:Circadian Rhythm; D017931:DNA Primers / Q000235:genetics; D006418:Heme / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008024:Ligands; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D056950:Period Circadian Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013053:Spectrophotometry
chemical_list: D017931:DNA Primers; D008024:Ligands; D010446:Peptide Fragments; C513312:Per2 protein, mouse; D056950:Period Circadian Proteins; D011994:Recombinant Proteins; D006418:Heme