Two decades have passed since the discovery of the tumor suppressor, PTEN. A multitude of biological functions have since been revealed, suggesting potential therapeutic applications for both PTEN activation (e.g., cancer) and inhibition (e.g., neuroregeneration). Nevertheless, PTEN's therapeutic suitability has been called into question due to its "risky" profile as a tumor suppressor. To evaluate PTEN function and its various roles in disease a number of molecules have so far been developed. However, intrinsic problems associated with phosphatase inhibition and PTEN's complex regulation via post-translational modifications hinder straightforward access to selective modulators. For this reason, central questions associated with PTEN targeting remain unanswered. In this perspective, we summarize current PTEN-targeting strategies and discuss potential approaches to modulate its functional dose, considering all stages of PTEN biogenesis from direct protein modulation to the targeting of relevant miRNAs as well as the PTEN gene and mRNA.

The design of high-affinity, RNA-binding ligands has proven very challenging. This is due to the unique structural properties of RNA, often characterized by polar surfaces and high flexibility. In addition, the frequent lack of well-defined binding pockets complicates the development of small molecule binders. This has triggered the search for alternative scaffolds of intermediate size. Among these, peptide-derived molecules represent appealing entities as they can mimic structural features also present in RNA-binding proteins. However, the application of peptidic RNA-targeting ligands is hampered by a lack of design principles and their inherently low bio-stability. Here, the structure-based design of constrained α-helical peptides derived from the viral suppressor of RNA silencing, TAV2b, is described. We observe that the introduction of two inter-side chain crosslinks provides peptides with increased α-helicity and protease stability. One of these modified peptides (B3) shows high affinity for double-stranded RNA structures including a palindromic siRNA as well as microRNA-21 and its precursor pre-miR-21. Notably, B3 binding to pre-miR-21 inhibits Dicer processing in a biochemical assay. As a further characteristic this peptide also exhibits cellular entry. Our findings show that constrained peptides can efficiently mimic RNA-binding proteins rendering them potentially useful for the design of bioactive RNA-targeting ligands.

The structure-based design of constrained alpha-helical peptides derived from the viral suppressor of RNA silencing TAV2b is described. We observe that the introduction of two inter-side chain crosslinks provides peptides with increased alpha-helicity and protease stability. One of these modified peptides (B3) shows high affinity for different double-stranded RNA structures including a palindromic siRNA as well as microRNA-21 and its precursor pre-miR-21. Notably, B3 binding to pre-miR-21 inhibits Dicer processing in a biochemical assay. As a further characteristic this peptide also exhibits cellular entry. <br>

Biomolecular assemblies composed of proteins and oligonucleotides play a central role in biological processes. While in nature, oligonucleotides and proteins usually assemble via non-covalent interactions, synthetic conjugates have been developed which covalently link both modalities. The resulting peptide-oligonucleotide conjugates have facilitated novel biological applications as well as the design of functional supramolecular systems and materials. However, despite the importance of concerted protein/oligonucleotide recognition in nature, conjugation approaches have barely utilized the synergistic recognition abilities of such com-plexes. Herein, the structure-based design of peptide-DNA conjugates that bind RNA through Watson-Crick base pairing combined with peptide-mediated major groove recognition is reported. Two distinct conjugate families with tunable binding characteristics have been designed to adjacently bind a particular RNA sequence. In the resulting ternary complex, their peptide elements are located in proximity, a feature that was used to enable an RNA-templated click reaction. The introduced structure-based design approach opens the door to novel functional biomolecular assemblies.

No abstract