The nonfibrillar amyloid beta-peptide induces apoptotic neuronal cell death: involvement of its C-terminal fusogenic domain.

The toxicity of the nonaggregated amyloid beta-peptide (1-40) [A beta(1-40)] on the viability of rat cortical neurons in primary culture was investigated. We demonstrated that low concentrations of A beta peptide, in a nonfibrillar form, induced a time- and dose-dependent apoptotic cell death, including DNA condensation and fragmentation. We compared the neurotoxicity of the A beta(1-40) peptide with those of several A beta-peptide domains, comprising the membrane-destabilizing C-terminal domain of A beta peptide (e.g., amino acids 29-40 and 29-42). These peptides reproduced the effects of the (1-40) peptide, whereas mutant nonfusogenic A beta peptides and the central region of the A beta peptide (e.g., amino acids 13-28) had no effect on cell viability. We further demonstrated that the neurotoxicity of the nonaggregated A beta peptide paralleled a rapid and stable interaction between the A beta peptide and the plasma membrane of neurons, preceding apoptosis and DNA fragmentation. By contrast, the peptide in a fibrillar form induced a rapid and dramatic neuronal death mainly through a necrotic pathway, under our conditions. Taken together, our results suggest that A beta induces neuronal cell death by either apoptosis and necrosis and that an interaction between the nonfibrillar C-terminal domain of the A beta peptide and the plasma membrane of cortical neurons might represent an early event in a cascade leading to neurodegeneration.

Molecular determinants of the interaction between the C-terminal domain of Alzheimer's beta-amyloid peptide and apolipoprotein E alpha-helices.

In a previous work, we predicted and demonstrated that the 29-42-residue fragment of beta-amyloid peptide (Abeta peptide) has in vitro capacities close to those of the tilted fragment of viral fusion proteins. We further demonstrated that apolipoprotein E2 and E3 but not apolipoprotein E4 can decrease the fusogenic activity of Abeta(29-42) via a direct interaction. Therefore, we suggested that this fragment is implicated in the neurotoxicity of Abeta and in the protective effects of apolipoprotein E in Alzheimer's disease. Because structurally related apolipoproteins do not interact with the Abeta C-terminal domain but inhibit viral fusion, we suggested that interactions existing between fusogenic peptides and apolipoproteins are selective and responsible for the inhibition of fusion. In this study, we simulated interactions of all amphipathic helices of apolipoproteins E and A-I with Abeta and simian immunodeficiency virus (SIV) fusogenic fragments by molecular modeling. We further calculated cross-interactions that do not inhibit fusion in vitro. The results suggest that interactions of hydrophobic residues are the major event to inhibit the fusogenic capacities of Abeta(29-42) and SIV peptides. Selectivity of those interactions is due to the steric complementarity between bulky hydrophobic residues in the fusogenic fragments and hydrophobic residues in the apolipoprotein C-terminal amphipathic helices.

Auxin binding proteins from maize coleoptiles: purification and molecular characterization.

To understand precisely the mechanisms by which hormones like auxins regulate plant differentiation and development, it is essential to isolate putative hormone receptors. We have purified the major auxin binding protein from maize coleoptiles to homogeneity. The protein has an apparent molecular weight of 22,000 Da and binds 1-naphthylacetic acid with a KD of 2.4 x 10(-7) M. Protein sequence analysis allowed the construction of oligonucleotide probes to isolate a corresponding cDNA coding for this protein. The open reading frame of this cDNA predicts a protein of 201 amino acids and 21,990 Da in size. The amino acid sequence includes a cleavable N-terminal signal sequence and a C-terminal signal element consisting of the amino acids Lys Asp Glu Leu known to be responsible for preventing secretion of proteins from the lumen of the endoplasmic reticulum.