| abstract |
truncated hemoglobins (TrHbs, 2/2Hb, 2/2 globins); group 1 (N). 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 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. They 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). Typical of the TrHb1s (N) group is a protein matrix tunnel. It includes a Mycobacterium tuberculosis TrHb1, Mt-trHbN, which is encoded by the glbN gene. Mt-trHbN is expressed during the Mycobacterium stationary phase, and plays a specific defense role against nitrosative stress. The cyanobacterium Synechococcus sp. PCC 7002 TrHb1 GlbN, is constitutively expressed, and likely also protects cells from reactive nitrogen species. |