Hemoglobin is present as a canonical alpha(2)beta(2) tetramer in dopaminergic neurons

Hemoglobin is the oxygen carrier in blood erythrocytes. Oxygen coordination is mediated by alpha(2)beta(2) tetrameric structure via binding of the ligand to the heme iron atom. This structure is essential for hemoglobin function in the blood. In the last few years, expression of hemoglobin has been found in atypical sites, including the brain. Transcripts for alpha and beta chains of hemoglobin as well as hemoglobin immunoreactivity have been shown in mesencephalic As dopaminergic neurons, whose selective degeneration leads to Parkinson's disease. To gain further insights into the roles of hemoglobin in the brain, we examined its quaternary structure in dopaminergic neurons in vitro and in vivo. Our results indicate that (i) in mouse dopaminergic cell line stably over-expressing alpha and beta chains, hemoglobin exists as an alpha(2)beta(2) tetramer; (ii) similarly to the over-expressed protein, endogenous hemoglobin forms a tetramer of 64 kDa; (iii) hemoglobin also forms high molecular weight insoluble aggregates; and (iv) endogenous hemoglobin retains its tetrameric structure in mouse mesencephalon in vivo. In conclusion, these results suggest that neuronal hemoglobin may be endowed with some of the biochemical activities and biological function associated to its role in erythroid cells. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins. (c) 2013 The Authors. Published by Elsevier B.V. All rights reserved.