Metal swap between Zn7-metallothionein-3 and amyloid-beta-Cu protects against amyloid-beta toxicity.

Aberrant interactions of copper and zinc ions with the amyloid-beta peptide (Abeta) potentiate Alzheimer's disease (AD) by participating in the aggregation process of Abeta and in the generation of reactive oxygen species (ROS). The ROS production and the neurotoxicity of Abeta are associated with copper binding. Metallothionein-3 (Zn(7)MT-3), an intra- and extracellularly occurring metalloprotein, is highly expressed in the brain and downregulated in AD. This protein protects, by an unknown mechanism, cultured neurons from the toxicity of Abeta. Here, we show that a metal swap between Zn(7)MT-3 and soluble and aggregated Abeta(1-40)-Cu(II) abolishes the ROS production and the related cellular toxicity. In this process, copper is reduced by the protein thiolates forming Cu(I)(4)Zn(4)MT-3, in which an air-stable Cu(I)(4)-thiolate cluster and two disulfide bonds are present. The discovered protective effect of Zn(7)MT-3 from the copper-mediated Abeta(1-40) toxicity may lead to new therapeutic strategies for treating AD.

Zinc(II) binds to the neuroprotective peptide humanin.

The abnormal accumulation of the peptide amyloid-beta in the form of senile (or amyloid) plaques is one of the hallmarks of Alzheimer's disease (AD). Zinc ions have been implicated in AD and plaques formation. Recently, the peptide humanin has been discovered. Humanin showed neuroprotective activity against amyloid-beta insults. Here the question investigated is if humanin could interact directly with Zn(II). It is shown that Zn(II) and its substitutes Cd(II)/Co(II) bind to humanin via a thiolate bond from the side chain of the single cysteine at position 8. The low intensity of the d-d bands of Co(II)-humanin indicated an octahedral coordination geometry. Titration experiments suggest that Zn(II) binds to humanin with an apparent affinity in the low muM range. This apparent Zn-binding affinity is in the same order as for amyloid-beta and glutathione and could thus be of physiological relevance.

Structural studies on 24P-IkappaBalpha peptide derived from a human IkappaB-alpha protein related to the inhibition of the activity of the transcription factor NF-kappaB.

The IkappaB-alpha protein, inhibitor of the transcription factor nuclear factor-kappaB (NF-kappaB), is a cellular substrate of beta-transducin repeat containing protein (beta-TrCP). beta-TrCP is the F-box protein component of an Skp1/Cul1/F-box (SCF)-type ubiquitin ligase complex. beta-TrCP targets the protein IkappaB-alpha for ubiquitination, followed by proteasome degradation. The SCF-beta-TrCP complex specifically recognizes an IkappaB-alpha peptide containing the DpSGXXpS motif in a phosphorylation-dependent manner. A fragment comprising 24 amino acids residues for the phosphorylated peptide at the two sites Ser32 and Ser36 and thus termed 24P-IkappaBalpha (P-IkappaBalpha21-44) was characterized conformationally by NMR spectroscopy and molecular dynamics simulation. In the free states, 24P-IkappaBalpha exhibits mainly a random coil conformation, although the presence of a nascent bend was detected between residues 30 and 36, flanked by two N- and C-terminal disordered regions. The bound conformation of the phosphorylated IkappaB-alpha peptide was obtained using transfer nuclear Overhauser effect spectroscopy (TRNOESY) experiments. To further elucidate the basis of the beta-TrCP interaction, a complex between 24P-IkappaBalpha peptide and beta-TrCP protein was studied using saturation transfer difference (STD) NMR experiments. The conformation of 24P-IkappaBalpha bound to beta-TrCP presents a bend corresponding to the 31DpSGLDpS36 motif and on both sides N- and C-terminal turn regions (Lys22-Asp31 and Met37-Glu43). The bound structure of the phosphorylated peptide suggests that these domains are crucial for the interaction of the peptide with its receptor showing the protons identified by STD NMR as exposed in close proximity to the beta-TrCP surface.