title: Functional and Spectroscopic Characterization of Chlamydomonas reinhardtii Truncated Hemoglobins.
abstract: The single-cell green alga Chlamydomonas reinhardtii harbors twelve truncated hemoglobins (Cr-TrHbs). Cr-TrHb1-1 and Cr-TrHb1-8 have been postulated to be parts of the nitrogen assimilation pathway, and of a NO-dependent signaling pathway, respectively. Here, spectroscopic and reactivity properties of Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4, all belonging to clsss 1 (previously known as group N or group I), are reported. The ferric form of Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4 displays a stable 6cLS heme-Fe atom, whereas the hexa-coordination of the ferrous derivative appears less strongly stabilized. Accordingly, kinetics of azide binding to ferric Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4 are independent of the ligand concentration. Conversely, kinetics of CO or NO2- binding to ferrous Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4 are ligand-dependent at low CO or NO2- concentrations, tending to level off at high ligand concentrations, suggesting the presence of a rate-limiting step. In agreement with the different heme-Fe environments, the pH-dependent kinetics for CO and NO2-binding to ferrous Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4 are characterized by different ligand-linked protonation events. This raises the question of whether the simultaneous presence in C. reinhardtii of multiple TrHb1s may be related to different regulatory roles.
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma Tor Vergata, Roma, Italy; Interuniversity Consortium for the Research on the Chemistry of Metals in Biological Systems, Bari, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Ciaccio
authors.affiliation: Department of Biochemistry and Molecular Biology, Faculty of Sciences, University of Córdoba, Cordoba, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Ocaña-Calahorro
authors.affiliation: Department of Chemistry "Ugo Schiff", University of Firenze, Sesto Fiorentino (FI), Italy.
authors.forename: Enrica
authors.initials: E
authors.lastname: Droghetti
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma Tor Vergata, Roma, Italy; Interuniversity Consortium for the Research on the Chemistry of Metals in Biological Systems, Bari, Italy.
authors.forename: Grazia R
authors.initials: GR
authors.lastname: Tundo
authors.affiliation: Department of Biochemistry and Molecular Biology, Faculty of Sciences, University of Córdoba, Cordoba, Spain.
authors.forename: Emanuel
authors.initials: E
authors.lastname: Sanz-Luque
authors.affiliation: Department of Sciences, Roma Tre University, Roma, Italy; National Institute of Nuclear Physics, Roma Tre University Section, Roma, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Polticelli
authors.affiliation: Department of Sciences, Roma Tre University, Roma, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Visca
authors.affiliation: Department of Chemistry "Ugo Schiff", University of Firenze, Sesto Fiorentino (FI), Italy.
authors.forename: Giulietta
authors.initials: G
authors.lastname: Smulevich
authors.affiliation: Interdepartmental Laboratory of Electron Microscopy, Roma Tre University, Roma, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Ascenzi
authors.affiliation: Department of Clinical Sciences and Translational Medicine, University of Roma Tor Vergata, Roma, Italy; Interuniversity Consortium for the Research on the Chemistry of Metals in Biological Systems, Bari, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Coletta
mesh_terms: D001386:Azides / Q000378:metabolism; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017422:Sequence Analysis, DNA; D013053:Spectrophotometry; D054793:Truncated Hemoglobins / Q000737:chemistry* / Q000145:classification / Q000378:metabolism*
chemical_list: D001386:Azides; D017931:DNA Primers; D054793:Truncated Hemoglobins; D007501:Iron