title: Phe28B10Induces Channel-Forming Cytotoxic Amyloid Fibrillation in Human Neuroglobin, the Brain-Specific Hemoglobin.
abstract: Since its discovery, neuroglobin (Ngb), a neuron-specific oxygen binding hemoglobin, distinct from the classical myoglobin and blood hemoglobin, has attracted attention as an endogenous neuroprotectant. Recent reports suggest that Ngb protects neurons from brain stroke, ischemic stress-induced degeneration, and other brain disorders. Proteins with a specific role in neuroprotection are often associated with neurodegeneration, as well, depending on the cellular environment or specific cellular triggers that tilt the balance one way or the other. This investigation explored the potential role of Ngb in amyloid fibril-related neuronal disorder. Ngb was capable of amyloid formation in vitro at neutral pH and ambient temperature, in both apo and holo forms, albeit at a slower rate in the holo form, unlike other hemoglobins that exhibit such behavior exclusively in the apo states. Elevated temperature enhanced the rate of fibril formation significantly. The B-helix, which is known to play a major role in Ngb ligand binding kinetics, was found to be amyloidogenic with the Phe28B10amino acid side chain as the key inducer of fibrillation. The Ngb amyloid fibril was also significantly cytotoxic to neuroblastoma cell lines, compared to those obtained from reference hemoglobins. The Ngb fibril probably promoted toxicity by inducing channel formation in the cell membrane, as investigated here using synthetic lipid bilayer membranes and the propidium iodide uptake assay. These findings imply that Ngb plays a role in neurodegenerative disorders in vivo, for which there seems to be indirect evidence by association. Ngb thus presents a novel prospect for understanding amyloid-related brain disorders beyond the limited set of proteins currently investigated for such diseases.
authors.affiliation: Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India.
authors.forename: Sheetal
authors.initials: S
authors.lastname: Uppal
authors.affiliation: Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India.
authors.forename: Amit Kumar
authors.initials: AK
authors.lastname: Singh
authors.affiliation: Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India.
authors.forename: Richa
authors.initials: R
authors.lastname: Arya
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Madras , Chennai 600036, India.
authors.forename: Debanjan
authors.initials: D
authors.lastname: Tewari
authors.affiliation: Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India.
authors.forename: Neha
authors.initials: N
authors.lastname: Jaiswal
authors.affiliation: Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India.
authors.forename: Abhijeet
authors.initials: A
authors.lastname: Kapoor
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Madras , Chennai 600036, India.
authors.forename: Amal Kanti
authors.initials: AK
authors.lastname: Bera
authors.affiliation: Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India.
authors.forename: Alo
authors.initials: A
authors.lastname: Nag
authors.affiliation: Department of Biochemistry, University of Delhi South Campus , New Delhi 110021, India.
authors.forename: Suman
authors.initials: S
authors.lastname: Kundu
mesh_terms: D000682:Amyloid / Q000737:chemistry*; D001921:Brain / Q000378:metabolism*; D045744:Cell Line, Tumor; D002942:Circular Dichroism; D005914:Globins / Q000737:chemistry* / Q000235:genetics; D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D046529:Microscopy, Electron, Transmission; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics; D000078787:Neuroglobin; D010649:Phenylalanine / Q000737:chemistry*; D013696:Temperature
chemical_list: D000682:Amyloid; D006454:Hemoglobins; D009419:Nerve Tissue Proteins; D000078787:Neuroglobin; D010649:Phenylalanine; D005914:Globins