Globin-like proteins in Caenorhabditis elegans: in vivo localization, ligand binding and structural properties
- Equal contributors
1 Department of Biomedical Sciences, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium
2 Institute of Physiology and Zürich Center for Integrative Human Physiology (ZIHP), University of Zürich, Winterthurerstrasse 190, CH-8057, Zürich, Switzerland
3 Department of Biomolecular Sciences and Biotechnology, University of Milano, Via Celoria 26, I-20133 Milano, Italy
4 Department of Physics, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium
5 Department of Physics, University of Genova, Via Dodecaneso 33 I-16146 Genova, Italy
6 INSERM U779, University of Paris 11, Hopital de Bicetre, Le Kremlin Bicêtre, 94275, France
7 Zoophysiology, Department of Biological Sciences, Aarhus University, C F Møllers Allé, Bygning 1131, DK-8000 Aarhus C, Denmark
8 Department of Biology, Ghent University, K L Ledeganckstraat 35, B-9000 Ghent, Belgium
BMC Biochemistry 2010, 11:17 doi:10.1186/1471-2091-11-17Published: 2 April 2010
The genome of the nematode Caenorhabditis elegans contains more than 30 putative globin genes that all are transcribed. Although their translated amino acid sequences fit the globin fold, a variety of amino-acid substitutions and extensions generate a wide structural diversity among the putative globins. No information is available on the physicochemical properties and the in vivo expression.
We expressed the globins in a bacterial system, characterized the purified proteins by optical and resonance Raman spectroscopy, measured the kinetics and equilibria of O2 binding and determined the crystal structure of GLB-1* (CysGH2 → Ser mutant). Furthermore, we studied the expression patterns of glb-1 (ZK637.13) and glb-26 (T22C1.2) in the worms using green fluorescent protein technology and measured alterations of their transcript abundances under hypoxic conditions.GLB-1* displays the classical three-over-three α-helical sandwich of vertebrate globins, assembled in a homodimer associated through facing E- and F-helices. Within the heme pocket the dioxygen molecule is stabilized by a hydrogen bonded network including TyrB10 and GlnE7.GLB-1 exhibits high ligand affinity, which is, however, lower than in other globins with the same distal TyrB10-GlnE7 amino-acid pair. In the absence of external ligands, the heme ferrous iron of GLB-26 is strongly hexacoordinated with HisE7, which could explain its extremely low affinity for CO. This globin oxidizes instantly to the ferric form in the presence of oxygen and is therefore incapable of reversible oxygen binding.
The presented data indicate that GLB-1 and GLB-26 belong to two functionally-different globin classes.