Saskia A. Bode

Reactions inside nanoscale protein cages

Chemical reactions are traditionally carried out in bulk solution, but in nature confined spaces, like cell organelles, are used to obtain control in time and space of conversion. One way of studying these reactions in confinement is the development and use of small reaction vessels dispersed in solution, such as vesicles and micelles. The utilization of protein cages as reaction vessels is a relatively new field and very promising as these capsules are inherently monodisperse, in that way providing uniform reaction conditions, and are readily accessible to both chemical and genetic modifications. In this review, we aim to give an overview of the different kinds of nanoscale protein cages that have been employed as confined reaction spaces.

Enzyme-Activatable Cell-Penetrating Peptides through a Minimal Side Chain Modification

Activatable cell-penetrating peptides are of great interest in drug delivery because of their enhanced selectivity which can be controlled by the external stimuli that trigger their activation. The use of a specific enzymatic reaction to trigger uptake of an inert peptide offers a relevant targeting strategy because the activation process takes place in a short time and only in areas where the specific cell surface enzyme is present. To this aim, the lysine side chain of Tat peptides was modified with an enzyme-cleavable domain of minimal size. This yielded blocked Tat-peptides which were inactive but that could be activated by coincubation with the selected enzymes.

Sensing cell adhesion using polydiacetylene-containing peptide amphiphile fibres

Sensing cell adhesion by means of a colourimetric response provides an intuitive measure of cell binding. In this study polydiacetylene-containing peptide amphiphiles fibres were designed to sense cell adhesion by means of a colour change. The diacetylene-containing peptide amphiphiles were functionalised with the cell-binding motif RGDS, and subsequently mixed with non-functionalised diacetylene-containing spacer amphiphiles. The diacetylenes in the backbone of these fibres were polymerised using UV-light to give dark blue fibre solutions. Subsequent cell adhesion induced a colour change from blue to pink. The propensity of the RGDS fibres to change colour upon cell adhesion could be tuned by varying the C-terminal amino acid of the spacer amphiphile. In addition to this, by varying the RGDS density we found that the optimum colourimetric response was obtained for fibres with a 6 : 1 ratio of non-RGDS to RGDS amphiphiles.

Coiled-Coil-Mediated Activation of Oligoarginine Cell-Penetrating Peptides

A supramolecular approach was undertaken to create functionally activatable cell‐penetrating peptides. Two tetra‐arginines were assembled into an active cell‐penetrating peptide by heterodimerizing leucine zippers. Three different leucine‐zipper pairs were evaluated: activation was found to depend on the association constant of the coiled‐coil peptides. The weaker‐binding peptides required an additional disulfide linkage to induce cell‐penetrating capability, whereas for the most‐stable coiled‐coil no additional stabilization was needed. The latter zipper pair was used to show that the induced formation of the coiled coils allows control over the uptake of an oligoarginine CPP‐conjugated cargo protein.

Click to enter: activation of oligo-arginine cell-penetrating peptides by bioorthogonal tetrazine ligations

The cellular uptake of a cell-penetrating peptide is controlled by reconstitution of two inactive halves using bioorthogonal tetrazine ligations and is applied to a fluorescently labelled protein.

Constrained cell penetrating peptides

In this review we provide an overview of recent developments in the field of cell penetrating peptides (CPPs) on research that aims to achieve better control over their transduction properties - one of the big challenges - by means of restraining them. Three different constraining strategies are presented: triggerable activation, backbone rigidification and macrocyclization. Each of these methods have their opportunities in gaining control over CPP activity and selectivity.