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Truncated Mb-fold globins, T family 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. 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. An example of a TrHb1 is Mycobacterium tuberculosis TrHb1/Mt-trHbN which is expressed during the Mycobacterium stationary phase, and plays a specific defense role against nitrosative stress. TrHb2s include the dimeric Arabidopsis thaliana TrHb2 AtGLB3. GLB3 is likely to have a function distinct from other plant globins: it exhibits a low O2 affinity, an unusual concentration-independent binding of O2 and CO, and does not respond to any of the treatments that induce plant 3-on-3 globins. TrHb3s include Campylobacter jejuni Ctb, encoded by Cj0465c, which may play a role in moderating O2 flux within C. jejuni. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",