InterPro domain: IPR016339

This entry represents a group of haemoglobin-like proteins found in eubacteria, cyanobacteria, protozoa, and plants, but not in animals or yeast [ 1 ]. Truncated hemoglobins (TrHbs) have a truncated 2-over-2 rather than the canonical 3-over-3 alpha-helical sandwich fold [ 2 ]. The variability of the amino acid residues of the heme pocket suggested their partition into three groups that share less than 30% sequence similarity with each other [ 3 ]. This entry includes:

• HbN (or GlbN): a truncated haemoglobin-like protein that binds oxygen cooperatively with a very high affinity and a slow dissociation rate, which may exclude it from oxygen transport. It appears to be involved in bacterial nitric oxide detoxification and in nitrosative stress [ 3 , 4 ].
• Cyanoglobin (or GlbN): a truncated haemoprotein found in cyanobacteria that has high oxygen affinity, and which appears to serve as part of a terminal oxidase, rather than as a respiratory pigment [ 5 ].

1. Truncated hemoglobins: a new family of hemoglobins widely distributed in bacteria, unicellular eukaryotes, and plants. J. Biol. Chem. 277, 871-4
2. Structural and functional properties of hemoglobins from unicellular organisms as revealed by resonance Raman spectroscopy. J. Inorg. Biochem. 99, 72-96
3. Oxygen binding and NO scavenging properties of truncated hemoglobin, HbN, of Mycobacterium smegmatis. FEBS Lett. 580, 4031-41
4. Theoretical study of the truncated hemoglobin HbN: exploring the molecular basis of the NO detoxification mechanism. J. Am. Chem. Soc. 127, 4433-44
5. Solution 1H NMR study of the heme cavity and folding topology of the abbreviated chain 118-residue globin from the cyanobacterium Nostoc commune. Biochemistry 39, 1389-99