Globin-like proteins in Caenorhabditis elegans: in vivo localization, ligand binding and structural properties.
BACKGROUND
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.


RESULTS
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 alpha-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.


CONCLUSIONS
The presented data indicate that GLB-1 and GLB-26 belong to two functionally-different globin classes.
Geuens
Eva
E
Department of Biomedical Sciences, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium.
Hoogewijs
David
D
Nardini
Marco
M
Vinck
Evi
E
Pesce
Alessandra
A
Kiger
Laurent
L
Fago
Angela
A
Tilleman
Lesley
L
De Henau
Sasha
S
Marden
Michael C
MC
Weber
Roy E
RE
Van Doorslaer
Sabine
S
Vanfleteren
Jacques
J
Moens
Luc
L
Bolognesi
Martino
M
Dewilde
Sylvia
S
D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D003001:Cloning, Molecular; D005914:Globins / Q000378:metabolism*; D008024:Ligands; D008958:Models, Molecular; D010100:Oxygen / Q000378:metabolism; D013059:Spectrum Analysis, Raman
D029742:Caenorhabditis elegans Proteins; C549786:GLB-1 protein, C elegans; C549787:GLB-26 protein, C elegans; D008024:Ligands; D005914:Globins; D010100:Oxygen