EPR investigation of the role of B10 phenylalanine in neuroglobin — Evidence that B10Phe mediates structural changes in the heme region upon disulfide-bridge formation

Abstract

The function of neuroglobin, a member of the vertebrate globin family, is still unknown. In human neuroglobin (NGB), the formation of a disulfide bridge between the CysCD7 and CysD5 is known to affect the heme environment and its ligand-binding kinetics. Here, we show by means of EPR that the PheB10 residue plays a key role in transmitting the structural information from the disulfide bridge to the heme-pocket region. While formation of a disulfide bridge in ferric wild-type NGB leads to a considerable change of its EPR parameters, only minor changes are observed in the case of ferric PheB10Leu NGB. Furthermore, wild-type NGB is found to be much more stable in the presence of H 2O 2 than its PheB10Leu or its HisE7Leu mutants. While tyrosyl radicals are induced in HisE7Leu NGB by the addition of H 2O 2, this is not the case for wild-type and PheB10Leu NGB. The results will be discussed in terms of the protein's putative functions.