Archaeal protoglobin structure indicates new ligand diffusion paths and modulation of haem-reactivity.
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 C2A-a strictly anaerobic methanogenic Archaea-is, 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 A 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 O(2), 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 O(2)/CO binding to the haem that favours O(2) ligation and anticooperativity in ligand binding. Both properties are exceptional within the Hb superfamily.
Nardini
Marco
M
Department of Biomolecular Sciences and Biotechnology, CNR-INFM, University of Milano, Via Celoria 26, Milano 20133, Italy.
Pesce
Alessandra
A
Thijs
Liesbet
L
Saito
Jennifer A
JA
Dewilde
Sylvia
S
Alam
Maqsudul
M
Ascenzi
Paolo
P
Coletta
Massimiliano
M
Ciaccio
Chiara
C
Moens
Luc
L
Bolognesi
Martino
M
D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism; D002248:Carbon Monoxide / Q000378:metabolism; D018360:Crystallography, X-Ray; D004058:Diffusion; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D017020:Methanosarcina / Q000737:chemistry*; D008958:Models, Molecular; D010100:Oxygen / Q000378:metabolism; D017433:Protein Structure, Secondary; D013816:Thermodynamics
D019843:Archaeal Proteins; D008024:Ligands; D006418:Heme; D002248:Carbon Monoxide; D010100:Oxygen