The three-dimensional structure of the globin domain of globin-coupled sensor from Geobacter sulfurreducens

The recently discovered globin-coupled sensors (GCS) are heme-containing two domain transducers, that mediate the cellular responses to metabolic and environmental stimuli, such as NO, CO and O2. In particular, the GCSs identified in the strict anaerobic -Proteobacteria Geobacter sulfurreducens and Geobacter metalloreducens may be involved in sulfate/sulfur reduction. They are composed of 300 amino acid residues and characterised by a N-terminal globin domain (162 amino acids) and by a bundle of four transmembrane helices at C-terminal1. Here, we present the X-ray three-dimensional structure of the globin domain of GCS from Geobacter sulfurreducens (Gs-GCS162), at 1.5 Å resolution. The crystal structure of ferric Gs-GCS162 was solved by MAD techniques (data collected at the synchrotron beamline ID23-1, ESRF, Grenoble, France), based on the heme Fe atom anomalous scattering. The Gs-GCS162 fold is a variant of the classical globin fold of myoglobin and hemoglobin, spanning helices A through H, with an additional Z helix at the N-terminus. The Gs-GCS162 displays a six-coordinated heme and is one of the first examples of bishistidyl hexacoordinated GCS. Strikingly, the distal heme-coordination is provided by a His residue located at the E11 topological site, an unprecedented feature within globins.