Dual Stimuli-Responsive Dynamic Covalent Peptide Tags: Toward Sequence-Controlled Release in Tumor-like Microenvironments

Abstract

Dynamic covalent chemistry (DCvC) has emerged as a versatile synthetic tool for devising stable, stimuli-responsive linkers or conjugates. The interplay of binding affinity, association and dissociation constants exhibits a strong influence on the selectivity of the reaction, the conversion rate, as well as the stability in aqueous solutions. Nevertheless, dynamic covalent interactions often exhibit fast binding and fast dissociation events or vice versa, affecting their conversion rates or stabilities. To overcome the limitation in linker design, we reported herein dual responsive dynamic covalent peptide tags combining a pH responsive boronate ester with fast association and dissociation rates, and a redox-active disulfide with slow formation and dissociation rate. Precoordination by boronic acid–catechol interaction improves self-sorting and selectivity in disulfide formation into heterodimers. The resulting bis-peptide conjugate exhibited improved complex stability in aqueous solution and acidic tumor-like extracellular microenvironment. Furthermore, the conjugate responds to pH changes within the physiological range as well as to redox conditions found inside cancer cells. Such tags hold great promise, through cooperative effects, for controlling the stability of bioconjugates under dilution in aqueous media, as well as designing intelligent pharmaceutics that react to distinct biological stimuli in cells.

A Peptide-Based Trap for Metal Ions Studied by Electron Paramagnetic Resonance

“…The spectral values are close to those of a monoradical species, but with a bit of extra line broadening (the peak-to-peak width of the central transition is 0.35 mT, while for mono-labeled trichogins, values of 0.26-0.33 mT were reported [44]). Previously, for Tri 1,8 in a polar solvent, we found the TOAC 1 -TOAC 8 distance to be above 1.5 nm [24]. Therefore, the broadening cannot be attributed to a through-space exchange coupling.…”

“…The peptide/Ca(II) ratio 2:1 produced a distance distribution function in the form of a broad line centered at around 1.75 nm and the width of about 0.25 nm (Figure S5). This distribution cannot be fitted by Tri 1,8 and Tri 1,8 +Ca(II) alone, but might come from a superimposition of those two lines. However, due to overlapping of functions, the deconvolution within the experimental accuracy is difficult and may lead to incorrect conclusions.…”

“…Indeed, the Fmoc group at the Nterminus is endowed with higher flexibility with respect to TOAC 1 in the Tric 1,8 analog. Therefore, Fmoc can get closer to TOAC 8 , as compared to the immobilized nitroxide of TOAC 1 . This possibility, in turn, accounts for the shorter distance observed by FRET in the Fmoc 0 -TOAC 8 analog.…”

“…In this connection, it is also worth considering a bidentate coordination from neighboring oxygens of the backbone. To further consider conformational implications, we created a model of Tri 1,8 in the 3 10 -helical structure using Avogadro software [73]. The O-O distance between two neighboring carbonyl groups in that model is about 3.9 Å, which is large enough for Na(I) and Ca(II) coordination and for Cu(II) axial coordination [39].…”

“…Peptides attract attention not only for their antibiotic activity [1][2][3] but also for applications in nanotechnology, as molecular sensors or logical elements, or as biomaterials for purifying water from environmental toxins [4][5][6][7][8]. Peptides are often able to provide a selective response to external stimuli, such as the presence of a specific analyte [9][10][11][12][13][14][15][16][17].…”