Studies of β-turn opening with model peptides containing non-coded α-amino isobutyric acid

Miniature β-Hairpin Mimetic by Intramolecular Hydrogen Bond and C-H···π Interactions

Canonically, protein β-hairpin motifs are stabilized by intramolecular hydrogen bonds. Here, we attempt to develop a rational design recipe for a miniature hairpin structure stabilized by hydrogen bonding as well as C-H···π interaction and try to understand how such a stabilization effect varies with different functional groups at each terminus. Database analysis shows that the α-amino acids with an aromatic side chain will not favor that kind of C-H···π stabilized hairpin structure. However, hybrid tripeptides with an N-terminal Boc-Trp-Aib corner residue and C-terminal aromatic ω-amino acids fold into the hairpin conformation with a central β-turn/open-turn that is reinforced by a C-H···π interaction. The CCDC database analysis further confirms that this C-H···π stabilized hairpin motif is general for Boc-protected tripeptides containing Aib in the middle and aromatic functionality at the C-terminus. The different α-amino acids like Leu/Ala/Phe/Pro/Ser at the N-terminus have a minor influence on the C-H···π interaction and stabilities of the folded structures in solid-state. However, the hybrid peptides exhibit different degrees of conformational heterogeneity both in the solid and solution phase, which is common for this kind of flexible small molecule. Conformational heterogeneity in the solution phase including the C-H···π stabilized β-hairpin structures are characterized by the molecular dynamics (MD) simulations explaining their plausible origin at an atomistic level.

Formation of supramolecular single and double helix-like structures from designed tripeptides

The conformation and self-assembly of N- and C-protected tripeptides, Boc-Gly-l-Phg-d-Phe-OMe (1, Phg: phenylglycine) and Boc-Gly-l-Phg-d-Phg-OMe (2), have been investigated.

Unique crystallographic signatures of Boc-Gly-Phe-Phe-OMe and Boc-Gly-Phg-Phe-OMe and their self-association

The crystal structures and morphology of Boc-Gly-Phe-Phe-OMe (1) and Boc-Gly-Phg-Phe-OMe (2) are reported. While 1 forms a rare open turn conformation, 2 forms a β-sheet conformation.

An auxin–tyrosine derivative based biocompatible supergelator: a template for fabrication of nanoparticles for sustained release of model drugs

This report reveals the supergelating ability of an auxin-tyrosine derivative based biocompatible hydrogel in drug delivery.

The Use of the Calcitonin Minimal Recognition Module for the Design of DOPA-Containing Fibrillar Assemblies

Amyloid deposits are insoluble fibrous protein aggregates, identified in numerous diseases, which self-assemble through molecular recognition. This process is facilitated by short amino acid sequences, identified as minimal modules. Peptides corresponding to these motifs can be used for the formation of amyloid-like fibrillar assemblies in vitro. Such assemblies hold broad appeal in nanobiotechnology due to their ordered structure and to their ability to be functionalized. The catechol functional group, present in the non-coded L-3,4-dihydroxyphenylalanine (DOPA) amino acid, can take part in diverse chemical interactions. Moreover, DOPA-incorporated polymers have demonstrated adhesive properties and redox activity. In this work, amyloid-like fibrillar assemblies were formed through the self-assembly of a pentapeptide containing DOPA residues, Asp-DOPA-Asn-Lys-DOPA. The design of this peptide was based on the minimal amyloidogenic recognition motif of the human calcitonin hormone, Asp-Phe-Asn-Lys-Phe, the first amyloidogenic pentapeptide identified. By substituting phenylalanine with DOPA, we obtained DOPA-functionalized amyloid-like assemblies in water. Electron microscopy revealed elongated, linear fibril-like nanometric assemblies. Secondary structure analysis indicated the presence of amyloid-characteristic β-sheet structures as well as random coil structures. Deposition of silver on the DOPA-incorporated assemblies suggested redox activity and demonstrated the applicative potential of this novel nanobiomaterial.

Design and self-assembly of a leucine-enkephalin analogue in different nanostructures: application of nanovesicles

An opioid (leucine-enkephalin) conformational analogue forms diverse nanostructures such as vesicles, tubes, and organogels through self-assembly. The nanovesicles encapsulate the natural hydrophobic drug curcumin and allow the controlled release through cation-generated porogens in membrane mimetic solvent.

N-(tert-butoxycarbonyl)-O-allyl-L-seryl-α-aminoisobutyryl-L-valine methyl ester: a protected tripeptide with an allylated serine residue

The title compound [systematic name (6S,12S)-methyl 6-(allyloxymethyl)-12-isopropyl-2,2,9,9-tetramethyl-4,7,10-trioxo-3-oxa-5,8,11-triazatridecan-13-oate], C(21)H(37)N(3)O(7), containing the little studied O-allyl-L-serine residue [Ser(All)], crystallizes in the monoclinic space group C2 with one molecule in the asymmetric unit. The compound is an analogue of the Ser140-Val142 segment of the water channel aquaporin-4 (AQP4). It forms a distorted type-II β-turn with a P(II)-3(10L)-P(II) backbone conformation (P(II) is polyproline II). The overall backbone conformation is markedly different from that of the CO(Pro139)-Val142 stretch of rat AQP4, but is quite similar to the corresponding segment of human AQP4, despite significant differences at the level of the individual residues. The side chain of the Ser(All) residue adopts a gauche conformation relative to the backbone CO-C(α) and C(α)-N bonds. The H atoms of the two CH(2) groups in the Ser(All) side chain are almost eclipsed. The crystal packing of the title compound is divided into one-molecule-thick layers, each layer having a hydrophilic core and distinct hydrophobic interfaces on either side.