Open AccessFunctional and Spectroscopic Characterization of Chlamydomonas reinhardtii Truncated Hemoglobins
Author(s) -
Chiara Ciaccio,
Francisco Ocaña-Calahorro,
Enrica Droghetti,
Grazia R. Tundo,
Emanuel Sanz-Luque,
Fabio Polticelli,
Paolo Visca,
Giulietta Smulevich,
Paolo Ascenzi,
Massimo Coletta
Publication year - 2015
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0125005
Subject(s) - chlamydomonas reinhardtii , ferrous , ligand (biochemistry) , kinetics , chemistry , protonation , ferric , reactivity (psychology) , heme , stereochemistry , crystallography , medicinal chemistry , inorganic chemistry , biochemistry , enzyme , receptor , organic chemistry , medicine , ion , physics , alternative medicine , pathology , quantum mechanics , mutant , gene
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 NO 2 − binding to ferrous Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4 are ligand-dependent at low CO or NO 2 − 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 NO 2 −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.