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Globin-like protein superfamily This globin-like domain superfamily contains a wide variety of all-helical proteins that bind porphyrins, phycobilins, and other non-heme cofactors, and play various roles in all three kingdoms of life, including sensors or transporters of oxygen. It includes the M/myoglobin-like, S/sensor globin, and T/truncated globin (TrHb) families, and the phycobiliproteins (PBPs). The M family includes chimeric (FHbs/flavohemoglobins) and single-domain globins: FHbs, Ngbs/neuroglobins, Cygb/cytoglobins, GbE/avian eye specific globin E, GbX/globin X, amphibian GbY/globin Y, Mb/myoglobin, HbA/hemoglobin-alpha, HbB/hemoglobin-beta, SDgbs/single-domain globins related to FHbs, and Adgb/androglobin. The S family includes GCS/globin-coupled sensors, Pgbs/protoglobins, and SSDgbs/sensor single domain globins. The T family is classified into three main groups: TrHb1s (N), TrHb2s (O) and TrHb3s (P). 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 (named A through H). For M family Adgbs, this globin domain is permuted, such that C-H are followed by A-B. 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. PBPs bind the linear tetrapyrrole chromophore, phycobilin, a prosthetic group chemically and metabolically related to iron protoporphyrin IX/protoheme. Examples of other globin-like domains which bind non-heme cofactors include those of the Bacillus anthracis sporulation inhibitors pXO1-118 and pXO2-61 which bind fatty acid and halide in vitro, and the globin-like domain of Bacillus subtilis RsbRA which is presumed to channel sensory input to the C-terminal sulfate transporter/ anti-sigma factor antagonist (STAT) domain. RsbRA is a component of the sigma B-activating stressosome, and a regulator of the RNA polymerase sigma factor subunit sigma (B). |
Jiyao W et al.(2023). "The conserved domain database in 2023.",