A strict requirement in proteasome substrates for spacing between ubiquitin tag and degradation initiation elements.

Proteins are typically targeted to the proteasome for degradation through the attachment of ubiquitin chains and the proteasome initiates degradation at a disordered region within the target protein. Yet some proteins with ubiquitin chains and disordered regions escape degradation. Here we investigate how the position of the ubiquitin chain on the target protein relative to the disordered region modulates degradation and show that the distance between the two determines whether a protein is degraded efficiently.

Mechanisms of substrate recognition by the 26S proteasome.

The majority of regulated protein degradation in eukaryotes is accomplished by the 26S proteasome, the large proteolytic complex responsible for removing regulatory proteins and damaged proteins. Proteins are targeted to the proteasome by ubiquitination, and degradation is initiated at a disordered region within the protein. The ability of the proteasome to precisely select which proteins to break down is necessary for cellular functioning.

Charge Distribution Fine-Tunes the Translocation of α-Helical Amphipathic Peptides across Membranes.

Hundreds of cationic antimicrobial and cell-penetrating peptides (CPPs) form amphipathic α-helices when bound to lipid membranes. Here, we test two hypotheses for the differences in the ability of these peptides to translocate across membranes. The first, which we now call the hydrophobicity hypothesis, is that peptide translocation is determined by the Gibbs energy of insertion into the bilayer from the membrane interface.

Translocation of cationic amphipathic peptides across the membranes of pure phospholipid giant vesicles.

The ability of amphipathic polypeptides with substantial net positive charges to translocate across lipid membranes is a fundamental problem in physical biochemistry. These peptides should not passively cross the bilayer nonpolar region, but they do. Here we present a method to measure peptide translocation and test it on three representative membrane-active peptides.

Hemolytic activity of membrane-active peptides correlates with the thermodynamics of binding to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayers.

Understanding the mechanisms of antimicrobial, cytolytic and cell-penetrating peptides is important for the design of new peptides to be used as cargo-delivery systems or antimicrobials. But these peptides should not be hemolytic. Recently, we designed a series of such membrane-active peptides and tested several hypotheses about their mechanisms on model membranes.