Title
Structure and haem-distal site plasticity in **Methanosarcina acetivorans** protoglobin Structure and haem-distal site plasticity in **Methanosarcina acetivorans** protoglobin
Author
Faculty/Department
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences . Biomedical Sciences
Publication type
article
Publication
Subject
Engineering sciences. Technology
Source (journal)
PLoS ONE
Volume/pages
8(2013) :6 , p. 1-14
ISSN
1932-6203
Article Reference
e66144
Carrier
E-only publicatie
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
Protoglobin from Methanosarcina acetivorans C2A (MaPgb), a strictly anaerobic methanogenic Archaea, is a dimeric haem-protein whose biological role is still unknown. As other globins, protoglobin can bind O-2, CO and NO reversibly in vitro, but it displays specific functional and structural properties within members of the hemoglobin superfamily. CO binding to and dissociation from the haem occurs through biphasic kinetics, which arise from binding to (and dissociation from) two distinct tertiary states in a ligation-dependent equilibrium. From the structural viewpoint, protoglobin-specific loops and a N-terminal extension of 20 residues completely bury the haem within the protein matrix. Thus, access of small ligand molecules to the haem is granted by two apolar tunnels, not common to other globins, which reach the haem distal site from locations at the B/G and B/E helix interfaces. Here, the roles played by residues Trp(60)B9, Tyr(61)B10 and Phe(93)E11 in ligand recognition and stabilization are analyzed, through crystallographic investigations on the ferric protein and on selected mutants. Specifically, protein structures are reported for protoglobin complexes with cyanide, with azide (also in the presence of Xenon), and with more bulky ligands, such as imidazole and nicotinamide. Values of the rate constant for cyanide dissociation from ferric MaPgb-cyanide complexes have been correlated to hydrogen bonds provided by Trp(60)B9 and Tyr(61)B10 that stabilize the haem-Fe(III)-bound cyanide. We show that protoglobin can strikingly reshape, in a ligand-dependent way, the haem distal site, where Phe(93)E11 acts as ligand sensor and controls accessibility to the haem through the tunnel system by modifying the conformation of Trp(60)B9.
Full text (open access)
https://repository.uantwerpen.be/docman/irua/33bd99/5081.pdf
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