A divergent synthetic strategy for generating helical p53 peptides bearing functionalised staple linkages, allowing for efficient optimisation of cellular activity.

Ure2 is the protein determinant of the [URE3] prion phenotype inHere we tested the effect of overexpression of Hsp40 members Ydj1, Sis1, and Apj1 and also Hsp70 co-chaperones Cpr7, Cns1, Sti1, and Fes1 in vivo and found that only Ydj1 showed a strong curing effect on [URE3]. We also investigated the interaction of Ydj1 with Ure2 in vitro. We found that Ydj1 was able to suppress formation of amyloid-like fibrils of Ure2 by delaying the process of fibril formation, as monitored by thioflavin T binding and atomic force microscopy imaging. Controls using bovine serum albumin, Sis1, or the human Hsp40 homologues Hdj1 or Hdj2 showed no significant inhibitory effect. Ydj1 was only effective when added during the lag phase of fibril formation, suggesting that it interacts with Ure2 at an early stage in fibril formation and delays the nucleation process. Using surface plasmon resonance and size exclusion chromatography, we demonstrated a direct interaction between Ydj1 and both wild type and N-terminally truncated Ure2. In contrast, Hdj2, which did not suppress fibril formation, did not show this interaction. The results suggest that Ydj1 inhibits Ure2 fibril formation by binding to the native state of Ure2, thus delaying the onset of oligomerization.The epigenetic factor [URE3] in the yeast Saccharomyces cerevisiae represents the prion form of the protein Ure2 (1). Like the mammalian prion, the heritable [URE3] phenotype is conveyed by a structural change in its protein determinant to an aggregated form (1, 2). Ure2 is a 354-amino acid homodimeric protein consisting of a relatively flexible and protease-sensitive N-terminal region (ϳ90 amino acids) and a globular C-terminal region (3-5). The N-terminal region is required for its prion properties in vivo (2) and to form amyloid-like filaments in vitro (6 -8). However, deletion of the N-terminal region has no detectable effect on the stability or folding of the protein in vitro (9). The C-terminal region, for which the crystal structure has been determined in both apo (5, 10) and glutathione-bound (11) forms, shows structural similarity to glutathione transferases (GSTs), 3 and is necessary and sufficient for its regulatory function in vivo: Ure2 interacts with the transcription factor Gln3, allowing control of nitrogen catabolite repression and blocking the uptake of poor nitrogen sources in the presence of a good nitrogen source (12, 13). In addition, Ure2 possesses glutathione-dependent peroxidase (GPx) activity, which is maintained upon formation of fibrillar aggregates, indicating that the C-terminal globular domains of Ure2 retain their native structure within the fibrils (14).Ydj1 from S. cerevisiae is a molecular chaperone of the type I Hsp40 family and is involved in multiple functions, including import of proteins into mitochondria, secretion of mating pheromones, and regulation of the activity of the cytoplasmic Hsp70s (15-17). Ydj1 can bind to nonnative polypeptides and pair with Hsp70 Ssa proteins to prevent aggregation and facilitate refolding of denatured p...

The 33-amino-acid ankyrin motif comprises a β-turn followed by two anti-parallel α-helices and a loop and tandem arrays of the motif pack in a linear fashion to produce elongated structures characterized by short-range interactions. In this article we use site-directed mutagenesis to investigate the kinetic unfolding mechanism of D34, a 426-residue, 12-ankyrin repeat fragment of the protein ankyrinR. The data are consistent with a model in which the N-terminal half of the protein unfolds first by unraveling progressively from the start of the polypeptide chain to form an intermediate; in the next step, the C-terminal half of the protein unfolds via two pathways whose transition states have either the early or the late C-terminal ankyrin repeats folded. We conclude that the two halves of the protein unfold by different mechanisms because the N-terminal moiety folds and unfolds in the context of a folded C-terminal moiety, which therefore acts as a “seed” and confers a unique directionality on the process, whereas the C-terminal moiety folds and unfolds in the context of an unfolded N-terminal moiety and therefore behaves like a single-domain ankyrin repeat protein, having a high degree of symmetry and consequently more than one unfolding pathway accessible to it