Title
Archaeal protoglobin structure indicates new ligand diffusion paths and modulation of haem-reactivity
Author
Faculty/Department
Faculty of Pharmaceutical, Biomedical and Veterinary Sciences . Biomedical Sciences
Publication type
article
Publication
Oxford ,
Subject
Biology
Human medicine
Source (journal)
EMBO reports. - Oxford, 2000, currens
Volume/pages
9(2008) :2 , p. 157-163
ISSN
1469-221X
1469-3178
ISI
000253778400012
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
The structural adaptability of the globin fold has been highlighted by the recent discovery of the 2-on-2 haemoglobins, of neuroglobin and cytoglobin. Protoglobin from Methanosarcina acetivorans C2Aa strictly anaerobic methanogenic Archaeais, to the best of our knowledge, the latest entry adding new variability and functional complexity to the haemoglobin (Hb) superfamily. Here, we report the 1.3 Å crystal structure of oxygenated M. acetivorans protoglobin, together with the first insight into its ligand-binding properties. We show that, contrary to all known globins, protoglobin-specific loops and an amino-terminal extension completely bury the haem within the protein matrix. Access of O2, CO and NO to the haem is granted by the protoglobin-specific apolar tunnels reaching the haem distal site from locations at the B/G and B/E helix interfaces. Functionally, M. acetivorans dimeric protoglobin shows a selectivity ratio for O2/CO binding to the haem that favours O2 ligation and anticooperativity in ligand binding. Both properties are exceptional within the Hb superfamily.
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