Zinc Interactions With Brain-Derived Neurotrophic Factor and Related Peptide Fragments.

Brain-derived neurotrophic factor (BDNF) is a neurotrophin essential for neuronal development and survival, synaptic plasticity, and cognitive function. Dysregulation of BDNF signaling is involved in several neurodegenerative disorders, including Alzheimer's disease. Alteration of metal ion homeostasis is observed both in normal aging and in many neurodegenerative diseases. Interestingly, there is a significant overlap between brain areas characterized by metal ion dyshomeostasis and those where BDNF exerts its biological activity. Therefore, it is reasonable to speculate that metal ions, especially zinc, can modulate the activity of BDNF. The synthesis of BDNF peptidomimetic can be helpful both to understand the molecular interaction of BDNF with metal ions and to develop new drugs for neurodegenerative diseases.

Neurotrophin-mimicking peptides at the biointerface with gold respond to copper ion stimuli.

The peptide fragments NGF1-14 and BDNF1-12, encompassing the N-terminal domains, respectively, of the proteins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) were used in this study for the fabrication of a hybrid gold/peptide biointerface. These peptides mimic the Trk receptor activation of the respective whole protein - with a crucial role played by copper ions - and exhibit, in bulk solution, a pH-dependent capability to complex copper. We demonstrate here the maintenance of peptide-specific responses at different pH values as well as the copper binding also for the adlayers formed upon physisorption at the gold surface. The physicochemical properties, including viscoelastic behavior of the adlayer and competitive vs. synergic interactions in sequential adsorption processes, were addressed both experimentally, by quartz crystal microbalance with dissipation monitoring (QCM-D) and circular dichroism (CD), and theoretically, by molecular dynamics (MD) calculations. Proof-of work biological assays with the neuroblastoma SY-SH5H cell line demonstrated that the developed hybrid Au/peptide nanoplatforms are very promising for implementation in pH- and metal-responsive systems for application in nanomedicine.

Copper binding to naturally occurring, lactam form of angiogenin differs from that to recombinant protein, affecting their activity.

Angiogenin is a member of the ribonuclease family and a normal constituent of human plasma. It is one of the most potent angiogenic factors known and is overexpressed in different types of cancers. Copper is also an essential cofactor in angiogenesis and, during this process, it is mobilized from inside to outside of the cell. To date, contrasting results have been reported about copper(ii) influencing angiogenin activity. However, in these studies, the recombinant form of the protein was used. Unlike recombinant angiogenin, that contains an extra methionine with a free terminal amino group, the naturally occurring protein present in human plasma starts with a glutamine residue that spontaneously cyclizes to pyroglutamate, a lactam derivative. Herein, we report spectroscopic evidence indicating that copper(ii) experiences different coordination environments in the two protein isoforms, and affects their RNase and angiogenic activity differently. These results show how relatively small differences between recombinant and wild type proteins can result in markedly different behaviours.

Nlgn4 knockout induces network hypo-excitability in juvenile mouse somatosensory cortex in vitro.

Neuroligins (Nlgns) are postsynaptic cell adhesion molecules that form transynaptic complexes with presynaptic neurexins and regulate synapse maturation and plasticity. We studied the impact of the loss of Nlgn4 on the excitatory and inhibitory circuits in somatosensory cortical slices of juvenile mice by electrically stimulating these circuits using a multi-electrode array and recording the synaptic input to single neurons using the patch-clamp technique. We detected a decreased network response to stimulation in both excitatory and inhibitory circuits of Nlgn4 knock-out animals as compared to wild-type controls, and a decreased excitation-inhibition ratio. These data indicate that Nlgn4 is involved in the regulation of excitatory and inhibitory circuits and contributes to a balanced circuit response to stimulation.

Prion proteins leading to neurodegeneration.

Prion diseases are fatal neurodegenerative disorders related to the conformational alteration of the prion protein (PrP C) into a pathogenic and protease-resistant isoform PrP(Sc). PrP(C) is a cell surface glycoprotein expressed mainly in the central nervous system and despite numerous efforts to elucidate its physiological role, the exact biological function remains unknown. Many lines of evidences indicate that prion is a copper binding protein and thus involved in the copper metabolism. Prion protein is not expressed only in mammals but also in other species such as birds, reptiles and fishes. However, it is noteworthy to point out that prion diseases are only observed in mammals while they seem to be spared to other species. The chicken prion protein (chPrP C) shares about 30% of identity in its primary sequence with mammal PrP C. Both types of proteins have an N-terminal domain endowed with tandem amino acid repeats (PHNPGY in the avian protein, PHGGGWQ in mammals), followed by a highly conserved hydrophobic core. Furthermore, NMR studies have highlighted a similar globular domain containing three alpha-helices, one short 3(10)-helix and a short antiparallel beta-sheet. Despite this structural similarity, it should be noted that the normal isoform of mammalian PrP C is totally degraded by proteinase K, while avian PrP C is not, thereby producing N-terminal domain peptide fragments stable to further proteolysis. Notably, the hexarepeat domain is considered essential for protein endocytosis, and it is supposed to be the analogous copper-binding octarepeat region of mammalian prion proteins. The number of copper binding sites, the affinity and the coordination environment of metal ions are still matter of discussion for both mammal and avian proteins. In this review, we summarize the similarities and the differences between mammalian and avian prion proteins, as revealed by studies carried out on the entire protein and related peptide fragments, using a range of experimental and computational approaches. In addition, we report the metal-driven conformational alteration, copper binding modes and the superoxide dismutase-like (SOD-like) activity of the related copper(II) complexes.

Electrospray mass spectrometric studies of L-carnosine (beta-alanyl-L-histidine) complexes with copper(II) or zinc ions in aqueous solution.

Electrospray ionization mass spectrometry (ESI-MS) was used for the speciation of supramolecular assemblies formed between equimolar amounts of carnosine and copper or zinc ions in dilute aqueous solutions. In the case of pure carnosine and carnosine/copper systems, the effect of pH changes, in the range 2-9, on the complexes surviving in solution was also explored. ESI data, besides supporting previous reported results on the formation of dimeric carnosine/copper and carnosine/zinc complexes, allowed a more complete speciation of the examined systems, bringing to light the existence of bis-complex species and, in the zinc case, the formation of oligomeric species. The data obtained for the systems investigated show that ESI-MS is not only a reliable and fast technique for the analysis of the metal/ligand systems, but also an interesting tool to obtain stoichiometric information on metal complexes formed in very low concentration solutions.