Human neuroglobin interacts with flotillin-1, a lipid raft microdomain-associated protein

Neuroglobin (Ngb) is a newly discovered vertebrate globin that is expressed in the brain and that can reversibly bind oxygen. It has been reported that Ngb levels increase in neurons in response to oxygen deprivation, and that it protects neurons from hypoxia. However, the mechanism of this neuroprotection remains unclear. Recently, we found that oxidized human Ngb bound to the alpha-subunits of heterotrimeric G proteins (Galpha) and acted as a guanine nucleotide dissociation inhibitor for Galpha. To identify other Ngb-binding proteins, we herein screened a human brain cDNA library by using a yeast two-hybrid system. Among the plasmids isolated from positive clones, one contained an insert with 100% sequence identity to human flotillin-1. The interaction of Ngb with flotillin-1 was confirmed by glutathione S-transferase pull-down experiments. Since Galpha exists within lipid rafts critical for signal transduction and flotillin-1 recruits signaling proteins to lipid rafts, flotillin-1 might recruit Ngb to lipid rafts as a means of preventing neuronal death.