Chiral Fibers Formation Upon Assembly of Tetraphenylalanine Peptide Conjugated to a PNA Dimer

Abstract

Self‐assembly of biomolecules such as peptides, nucleic acids or their analogues affords supramolecular objects, exhibiting structures and physical properties dependent on the amino‐acid or nucleobase composition. Conjugation of the peptide diphenylalanine (FF) to peptide nucleic acids triggers formation of self‐assembled structures, mainly stabilized by interactions between FF. In this work we report formation of homogeneous chiral fibers upon self‐assembly of the hybrid composed of the tetraphenylalanine peptide (4F) conjugated to the PNA dimer adenine‐thymine (at). In this case nucleobases seem to play a key role in determining the morphology and chirality of the fibers. When the PNA “at” is replaced by guanine‐cytosine dimer “gc”, disordered structures are observed. Spectroscopic characterization of the self‐assembled hybrids, along with AFM and SEM studies is reported. Finally, a structural model consistent with the experimental evidence has also been obtained, showing how the building blocks of 4Fat arrange to give helical fibers.

Tryptophan-PNA gc Conjugates Self-Assemble to Form Fibers

“…The PNA sequences were chosen in order to allow for the interaction between two different PNA-peptide units by base stacking and Watson-Crick hydrogen bonds. In fact, we have reported that stacking interactions stabilize aggregates when “gc” is conjugated to FF; formation of hydrogen bonds between “at” pairs has been reported in fibers formed by FFFF-at conjugates. , In the last case, formation of an antiparallel beta sheet is driven by the interactions between the peptides; the nucleobases seem to play a role in “zipping” the sheets.…”

“…Investigation of NMR spectra points out that, similar to what was observed for the FFFFgc peptide/PNA conjugate, the gc PNA dimer acts as a spared fragment presenting multiple conformers (Figure S10). ,, The NOESY spectrum of WWgc recorded at 10 mg/mL contains many negative NOEs that reflect a certain slower tumbling of the compound possibly induced by aggregation phenomena (Figure S11). We were unable to achieve unambiguous proton resonance assignments due to the presence in solution of multiple conformers (Figure S11A) and the extensive spectral overlaps particularly affecting the regions containing correlations from tryptophans and PNA bases aromatic protons (Figure S11B).…”

“…Stacking interactions between nucleobases seem to play a role in the formation of such structures . The increase in the length of the peptide along with a change in the nucleobase composition drives formation of fibers: in fact, when FFFF is conjugated to the PNA dimer “at” the combination of antiparallel peptide sheets with Watson Crick hydrogen bonds between complementary bases results in formation of chiral fibers . PNAs bearing amino-acid side chains in the gamma position of the backbone were employed to produce amphiphile PNAs, termed bilingual PNAs.…”

“…17 drives formation of fibers: in fact, when FFFF is conjugated to the PNA dimer "at" the combination of antiparallel peptide sheets with Watson Crick hydrogen bonds between complementary bases results in formation of chiral fibers. 18 PNAs bearing amino-acid side chains in the gamma position of the backbone were employed to produce amphiphile PNAs, termed bilingual PNAs. These PNAs with alanine or lysine side chains self-assemble, thanks to the interaction between the amphiphile side chain, and disassemble upon addition of oligonucleotides.…”

Highly Synergistic Properties of Multicomponent Hydrogels Thanks to Cooperative Nucleopeptide Assemblies

“…Thus, we report herein on a series for nucleopeptides built from the short amphipathic tetrapeptide Phe–Glu–Phe–Lys (i.e., FEFK) on which PNA strands of two units were incorporated at the N-term, improving the nucleobase/amino acid ratio to 1/2 to favor the impact and recognition of nucleobases. Herein, PNA derivatives, already considered for the development of nucleopeptides by our group , and others, , were chosen thanks to their high chemical stability, the more stable pairing they form, their simplicity of chemical synthesis (and of scalability), and their relevance in material science and for biological applications. , Thus, two PNA sequences were selected, each containing one purine and one non-complementary pyrimidine, namely, adenine–cytosine (AC) and thymine–guanine (TG) (Figure A), which are complementary sequences but not self-complementary in order to avoid homomolecular interactions and favor heteromolecular ones, sine qua non conditions to reach synergistic effects and innovative properties, thanks to peptide/peptide and nucleobase/nucleobase interactions, as shown in Figure B. Hence, a series of five compounds (Figure A), both amidated and acetylated at their C- and N-term, respectively, were synthesized on the solid support at a 800 μmol-scale: p­(TG)-FEFK and p­(AC)-FEFK and also the two controls p­(CC)-FEFK and p­(TT)-FEFK (for which the design will be discussed vide infra), and the nucleobase-lacking native peptide FEFK.…”