Zinc is required for structural stability of the C-terminus of archaeal translation initiation factor aIF2beta.

aIF2beta is an archaeal homolog of eukaryotic translation factor eIF2beta necessary for translation initiation and involved in recognition of the initiation codon. In the present study, we demonstrate for the first time zinc binding to the C2-C2 zinc finger at the C-terminus of aIF2beta. Nuclear magnetic resonance backbone assignments were also determined and the secondary structural elements identified.

The amyloid precursor protein interacts with neutral lipids.

The amyloid protein precursor (APP) was incorporated into liposomes or phospholipid monolayers. APP insertion into liposomes required neutral lipids, such as L-alpha-phosphatidylcholine, in the target membrane. It was prevented in vesicles containing L-alpha-phosphatidylserine. The insertion was enhanced in acidic solutions, suggesting that it is modulated by specific charge/charge interactions. Surface-active properties and behaviour of APP were characterized during insertion of the protein in monomolecular films of L-alpha-phosphatidylcholine, L-alpha-phosphatidylethanolamine or L-alpha-phosphatidylserine. The presence of the lipid film enhanced the rate of adsorption of the protein at the interface, and the increase in surface pressure was consistent with APP penetrating the lipid film. The adsorption of APP on the lipid monolayers displayed a significant head group dependency, suggesting that the changes in surface pressure produced by the protein were probably affected by electrostatic interactions with the lipid layers. Our results indicate that the penetration of the protein into the lipid monolayer is also influenced by the hydrophobic interactions between APP and the lipid. CD spectra showed that a large proportion of the alpha-helical secondary structure of APP remained preserved over the pH or ionic strength ranges used. Our findings suggest that APP/membrane interactions are mediated by the lipid composition and depend on both electrostatic and hydrophobic effects, and that the variations observed are not due to major secondary structural changes in APP. These observations may be related to the partitioning of APP into membrane microdomains.

Solution structure of the orphan PABC domain from Saccharomyces cerevisiae poly(A)-binding protein.

We have determined the solution structure of the PABC domain from Saccharomyces cerevisiae Pab1p and mapped its peptide-binding site. PABC domains are peptide binding domains found in poly(A)-binding proteins (PABP) and are a subset of HECT-family E3 ubiquitin ligases (also known as hyperplastic discs proteins (HYDs)). In mammals, the PABC domain of PABP functions to recruit several different translation factors to the mRNA poly(A) tail. PABC domains are highly conserved, with high specificity for peptide sequences of roughly 12 residues with conserved alanine, phenylalanine, and proline residues at positions 7, 10, and 12. Compared with human PABP, the yeast PABC domain is missing the first alpha helix, contains two extra amino acids between helices 2 and 3, and has a strongly bent C-terminal helix. These give rise to unique peptide binding specificity wherein yeast PABC binds peptides from Paip2 and RF3 but not Paip1. Mapping of the peptide-binding site reveals that the bend in the C-terminal helix disrupts binding interactions with the N terminus of peptide ligands and leads to greatly reduced binding affinity for the peptides tested. No high affinity or natural binding partners from S. cerevisiae could be identified by sequence analysis of known PABC ligands. Comparison of the three known PABC structures shows that the features responsible for peptide binding are highly conserved and responsible for the distinct but overlapping binding specificities.