Copper, BDNF and its N-terminal domain: Inorganic features and biological perspectives

Abstract

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that influences development, maintenance, survival, and synaptic plasticity of central and peripheral nervous systems. Altered BDNF signaling is involved in several neurodegenerative disorders including Alzheimer's disease. Metal ions may influence the BDNF activity and it is well known that the alteration of Cu 2+ homeostasis is a prominent factor in the development of neurological pathologies. The N-terminal domain of BDNF represents the recognition site of its specific receptor TrkB, and metal ions interaction with this protein domain may influence the protein/receptor interaction. In spite of this, no data inherent the interaction of BDNF with Cu2+ ions has been reported up to now. Cu2+ complexes of the peptide fragment BDNF(1-12) encompassing the sequence 1-12 of N-terminal domain of human BDNF protein were characterized by means of potentiometry, spectroscopic methods (UV/Vis, CD, EPR), parallel tempering simulations and DFT-geometry optimizations. Coordination features of the acetylated form, Ac-BDNF(1-12), were also characterized to understand the involvement of the terminal amino group. Whereas, an analogous peptide, BDNF(1-12)D3N, in which the aspartate residue was substituted by an asparagine, was synthesized to provide evidence on the possible role of carboxylate group in Cu2+ coordination. The results demonstrated that the amino group is involved in metal binding and the metal coordination environment of the predominant complex species at physiological pH consisted of one amino group, two amide nitrogen atoms, and one carboxylate group. Noteworthy, a strong decrease of the proliferative activity of both BDNF(1-12) and the whole protein on a SHSY5Y neuroblastoma cell line was found after treatment in the presence of Cu2+. The effect of metal addition is opposite to that observed for the analogous fragment of nerve growth factor (NGF) protein, highlighting the role of specific domains, and suggesting that Cu2+ may drive different pathways for the BDNF and NGF in physiological as well as pathological conditions. Key complex: Brain-derived neurotrophic factor (BDNF) N-terminal domain binds copper(II) with the involvement of His-1 α-amino group and Asp-3 carboxylate. The peptide encompassing the sequence 1-12 of the amino-terminal domain (BDNF(1-12)) of human BDNF is able to bind Cu2+. The predominant Cu2+ complex species, at physiological pH, is the [CuH-2L]2- in which the metal ion is bound to an amino group, two amide nitrogen atoms, and a carboxylate group (NH2, 2N-, COO-Asp) in a planar environment (see figure). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.