Truncated hemoglobins, group 2 (O); Mycobacterium tuberculosis hemoglobin O like
The M- and S families exhibit the canonical secondary structure of hemoglobins, a 3-over-3 alpha-helical sandwich structure (3/3 Mb-fold), built by eight alpha-helical segments. Truncated hemoglobins (TrHbs, 2/2Hb, or 2/2 globins) or the T family globins adopt a 2-on-2 alpha-helical sandwich structure, resulting from extensive and complex modifications of the canonical 3-on-3 alpha-helical sandwich that are distributed throughout the whole protein molecule. TrHbs are classified into three main groups based on their structural properties and named after Mycobacterium sp. genes glbN, glbO, and glbP: TrHb1s (N), TrHb2s (O) and TrHb3s (P). This group includes a Mycobacterium tuberculosis TrHb2, Mt-trHbO, encoded by the Mycobacterium tuberculosis glbO gene, which is expressed throughout the Mycobacterium growth phase. It also includes a TrHb2 from the thermophilic Thermobifida fusca ( Tf-trHb) which has a high thermostability and at the optimal growth temperature for Thermobifida fusca (between 55 and 60 degrees C ), it is capable of efficient O2 binding and release. Tf-trHb shares a relatively slow rate of oxygen binding with Mt-trHbO.
Jiyao W et al.(2023). "The conserved domain database in 2023.",