| dc.description.abstracteng | Cellular membranes contain a vast variety of proteins, which are practically required for every vital mechanism, such as selective transportation of ions and organic molecules, cell-cell recognition and signal transduction.[1] Nowadays, the major concern in life science is to gather an overview about the thermodynamics and kinetics that govern the native folding and aggregational behavior of these proteins. Artificially folded polymers, or foldamers, have attracted the interest of many research groups since they showed the potential for considerable versatilityin biological functions akin to natural proteins.[2] Thus, the prudent preorganization and refinement of such molecules can shed light on the molecular forces that control the structural features of membrane proteins and thereby, explore the correlation between their conformational stability and biological activity.
In particular, β-peptides have recently been used as very promising peptide mimics with interesting conformational and functional propensities. These non-biological polymers are stable towards enzymatic degradation and they can fold into compact multihelical structures including the 14- and the 12-helix.[3] Generally, introducing non-covalent interactions, such as hydrogen bonds and Vander Waals forces via interhelical side chains can enhance the three-dimensional stability of proteins. In this regard, β-peptides have been largely utilized as suitable folding patterns to provide information about self-assembly processes.[4-6]
Based on this concept, the main goal of this study is to understand the dynamics and the molecular interactions of transmembrane peptides using the most common β-peptide helices, the 14- and the 12-helix, as scaffolds to introduce polar residues across turns of the helix. This preorganization is expected to strongly promote self-assembly of these helices within membranes by means of interhelical forces. Thus, the architecture of the β-peptides used in this study was based on the choice of amino acids that can preferentially induce the formation of stable 14- and 12-helices. Subsequently, one side of these helices would be functionalized with one, two and three polar β3-glutamine residues respectively to reinforce helix-helix interactions via hydrogen bonds.
As a first step, the synthetic route of β-peptides containing a large amount of hydrophobic β-residues will be developed usingmanual microwave-assisted Fmoc-solid phase peptide synthesis (SPPS). Then, the ability of each of these β-peptides to adopt a rigid and a specific secondary structure either in solution or within large unilamellar vesicles (LUVs) composed of POPC will be monitored by CD spectroscopy. The membrane insertion of all the peptide barrel will be confirmed by virtue of tryptophan fluorescence of the β3-Trp introduced near the end of the sequences.
Additionally, the self-assembly process of these transmembrane helices inside POPC LUVs will be determined using Förster Resonance Energy Transfer (FRET). For this purpose, a donor-acceptor pair will be covalently attached to all the helices in order to generate their corresponding fluorescent analogues.
The backbone of the 14- and the 12-helix vary widely in terms of their conformational properties. Based on this notion, it is expected that the self-assembly of these two helices might vary as well according to their propensities to adopt discrete types of assemblies. Therefrom, the dissimilarity (or similarity) of these helices to arrange into different three-dimensional structures will be examined.
As a last step, to investigate the possibility of higher aggregation, the conformational features of the peptide barrel will be used by introducing polar residues across two sides of the helix. Then, the aggregational behavior will be determined using FRET. | de |