Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Biochemistry & Molecular Biology, Electron Paramagnetic Resonance (EPR), Hemoglobin, Kinetics, Oxygen Binding, Redox Signaling, ELECTRON-PARAMAGNETIC-RESONANCE, FMRFAMIDE-RELATED NEUROPEPTIDE, CYTOCHROME-C PEROXIDASE, LIGAND-BINDING, NITRIC-OXIDE, PROTEIN-STRUCTURE, GENE FAMILIES, HORSERADISH-PEROXIDASE, PROTOHEME PROTEINS, NATURAL VARIATION, Amino Acid Sequence, Animals, Ascaris suum, Caenorhabditis elegans, Caenorhabditis elegans Proteins, Gene Expression, Globins, Heme, Hydrogen-Ion Concentration, Iron, Models, Molecular, Molecular Sequence Data, Myoglobin, Nitrite Reductases, Oxidation-Reduction, Oxygen, Protein Binding, Protein Structure, Secondary, Protein Structure, Tertiary, Receptors, Neuropeptide, Recombinant Proteins, Sequence Homology, Amino Acid, 03 Chemical Sciences, 06 Biological Sciences, 11 Medical and Health Sciences, 31 Biological sciences, 32 Biomedical and clinical sciences, 34 Chemical sciences

Abstract:

We report the structural and biochemical characterization of GLB-33, a putative neuropeptide receptor that is exclusively expressed in the nervous system of the nematode Caenorhabditis elegans. This unique chimeric protein is composed of a 7-transmembrane domain (7TM), GLB-33 7TM, typical of a G-protein-coupled receptor, and of a globin domain (GD), GLB-33 GD. Comprehensive sequence similarity searches in the genome of the parasitic nematode, Ascaris suum, revealed a chimeric protein that is similar to a Phe-Met-Arg-Phe-amide neuropeptide receptor. The three-dimensional structures of the separate domains of both species and of the full-length proteins were modeled. The 7TM domains of both proteins appeared very similar, but the globin domain of the A. suum receptor surprisingly seemed to lack several helices, suggesting a novel truncated globin fold. The globin domain of C. elegans GLB-33, however, was very similar to a genuine myoglobin-type molecule. Spectroscopic analysis of the recombinant GLB-33 GD showed that the heme is pentacoordinate when ferrous and in the hydroxide-ligated form when ferric, even at neutral pH. Flash-photolysis experiments showed overall fast biphasic CO rebinding kinetics. In its ferrous deoxy form, GLB-33 GD is capable of reversibly binding O2 with a very high affinity and of reducing nitrite to nitric oxide faster than other globins. Collectively, these properties suggest that the globin domain of GLB-33 may serve as a highly sensitive oxygen sensor and/or as a nitrite reductase. Both properties are potentially able to modulate the neuropeptide sensitivity of the neuronal transmembrane receptor.