Human Brain Neuroglobin Structure Reveals a Distinct Mode of Controlling Oxygen Affinity

Neuroglobin, mainly expressed in vertebrate brain and retina, is a recently identified member of the globin superfamily. Augmenting O 2 supply, neuroglobin promotes survival of neurons upon hypoxic injury, potentially limiting brain damage. In the absence of exogenous ligands, neuroglobin displays a hexacoordinated heme. O 2 and CO bind to the heme iron, displacing the endogenous HisE7 heme distal ligand. Hexacoordinated human neuroglobin displays a classical globin fold adapted to host the reversible bis-histidyl heme complex and an elongated protein matrix cavity, held to facilitate O 2 diffusion to the heme. The neuroglobin structure suggests that the classical globin fold is endowed with striking adaptability, indicating that hemoglobin and myoglobin are just two examples within a wide and functionally diversified protein homology superfamily.