A Peptidomimetic Fluorescent Probe to Detect the Trypsin β2 Subunit of the Human 20S Proteasome

20S proteasome hydrolysis of LLVY substrates to determine preferences for moieties in its primed substrate channel

The proteasome is an essential multi-catalytic enzyme in cells that is responsible for degrading proteins with a ubiquitin-dependent or -independent mechanism. Many activity-based probes, inhibitors, and stimulators have been developed to study or modulate the activity of the proteasome. The development of these proteasome probes or inhibitors have been based on their interaction with the amino acids of the β5 substrate channel proceeding the catalytically active threonine residue. There is potential for positive interactions with a substrate to increase selectivity or cleavage rate with the β5 substrate channel after the catalytic threonine as evidenced by the proteasome inhibitor belactosin. To study what moieties the proteasome could accept in its primed substrate channel, we developed a liquid chromatography- mass spectrometry (LC-MS) method to quantitate the cleavage of substrates by purified human proteasome. This method allowed us to rapidly evaluate proteasome substrates that contain a moiety that could interact with the S1' site of the β5 proteasome channel. We were able to determine a preference for a polar moiety at the S1' substrate position. We believe this information can be used in the design of future inhibitors or activity-based probes for the proteasome.

Novel Cell Permeable Polymers of N-Substituted L-2,3-Diaminopropionic Acid (DAPEGs) and Cellular Consequences of Their Interactions with Nucleic Acids

The present study aimed to synthesize novel polycationic polymers composed of N-substituted L-2,3-diaminopropionic acid residues (DAPEGs) and investigate their cell permeability, cytotoxicity, and DNA-binding ability. The most efficient cell membrane-penetrating compounds (O2Oc-Dap(GO2)_n-O2Oc-NH₂, where n = 4, 6, and 8) showed dsDNA binding with a binding constant in the micromolar range (0.3, 3.4, and 0.19 µM, respectively) and were not cytotoxic to HB2 and MDA-MB-231 cells. Selected compounds used in the transfection of a GFP plasmid showed high transfection efficacy and minimal cytotoxicity. Their interaction with plasmid DNA and the increasing length of the main chain of tested compounds strongly influenced the organization and shape of the flower-like nanostructures formed, which were unique for 5/6-FAM-O2Oc-[Dap(GO2)]₈-O2Oc-NH₂ and typical for large proteins.