Fig. 2: X-ray structure of CbA5H^WT crystallized under aerobic conditions (CbA5H^air).

a Cartoon structure of CbA5H^air (PDB ID: 6TTL, chain A; see Supplementary Figure 2 for the homodimer). H- and F-domain are colored in yellow, the N-terminal SLBB domain (soluble ligand binding β-grasp)⁵¹ is presented in green. b Anomalous electron density map, depicting the positions and distances between iron-sulfur clusters, including the H-cluster (stick model), the two F-clusters (FS4A and FS4B) and the additional N-terminal cluster within the SLBB domain (FS4*) located more than 20 Å away from any other cluster. c Potential cluster coordination site within the SLBB domain, consisting of 3 cysteine and one histidine ligand. d, e CbA5H^air exhibits a characteristic structural displacement of the peptide loop containing C367 (TSC-loop) nearby the [2Fe]_H-cluster. d The omit map (Fo-Fc) was contoured at 2 σ (see Supplementary Fig. 17 for a more detailed structural comparison between the loop regions of CpI and CbA5H^air). e Structural alignment, depicting conformational differences between CbA5H^air (yellow) and CpI (white). Panels d and e focus on the [2Fe]_H-cluster and side chains of amino acids which influence anaerobic inactivation, O₂-resistance, and H_inact formation. f Selected parts of an amino acid sequence alignment of CbA5H^WT and CpI, including the polypeptide positions that influence TSC-loop reconfiguration and H_inact state formation in CbA5H^WT.