VHb (hemoglobin)

Vitreoscilla haemoglobin (VHb) is a type of haemoglobin found in the Gram-negative aerobic bacterium, Vitreoscilla. It is the first haemoglobin discovered from bacteria, but unlike classic hemoglobin it is composed only of a single globin molecule.[1]

Discovery

VHb was first discovered by Dale Webster in 1966 from a Vitreoscilla species. Being a soluble protein, and its close similarities of its spectral properties to those of bacterial cytochrome oxidase (cytochrome o), it was initially identified as “soluble cytochrome o”.[2] The real nature of VHb as a hemoglobin rather than a soluble cytochrome was resolved only after the amino acid sequence determined in 1986. The amino acid sequence revealed that it is made up of a single globin domain without additional structural elements, in contrast to typical haemoglobin. Yet the solution of its crystal structure confirmed that the three-dimensional structure of is remarkably similar to the classic globin fold.[3]

VHb is produced by the gene (vgb) which was cloned in 1988.[4]

Function

VHb is the best understood of all the bacterial haemoglobins, and is attributed to play a number of functions. Its main role is likely the binding of oxygen at low concentrations and its direct delivery to the terminal respiratory oxidase(s) such as cytochrome o. It is also involved in the delivery of oxygen to oxygenases, detoxification of NO by converting it to nitrate, and sensing oxygen concentrations and passing this signal to transcription factors.[1][3] It has a peroxidase-like activity and effectively eliminate autoxidation-derived H2O2, which is a cause of haeme degradation and iron release.[5]

References
  1. Stark BC, Dikshit KL, Pagilla KR (2012). "The Biochemistry of Vitreoscilla hemoglobin". Computational and Structural Biotechnology Journal. 3 (4): e201210002. doi:10.5936/csbj.201210002. PMC 3962134.
  2. Webster DA, Hackett DP (1966). "The purification and properties of cytochrome o from Vitreoscilla". J Biol Chem. 241 (14): 3308–3315. PMID 5913119.
  3. Stark BC, Dikshit KL, Pagilla KR (2011). "Recent advances in understanding the structure, function, and biotechnological usefulness of the hemoglobin from the bacterium Vitreoscilla". Biotechnol Lett. 33 (9): 1705–1714. doi:10.1007/s10529-011-0621-9. PMID 21603987.
  4. Dikshit KL, Webster DA (1988). "Cloning, characterization and expression of the bacterial globin gene from Vitreoscilla in Escherichia coli". Gene. 70 (2): 377–386. doi:10.1016/0378-1119(88)90209-0. PMID 2850971.
  5. Isarankura-Na-Ayudhya C, Tansila N, Worachartcheewan A, Bülow L, Prachayasittikul V (2010). "Biochemical and cellular investigation of Vitreoscilla hemoglobin (VHb) variants possessing efficient peroxidase activity". J Microbiol Biotechnol. 20 (3): 532–541. PMID 20372024.
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