Hybride aus Transmembranpeptiden und Peptidnucleinsäuren als Modellsystem für SNARE-Protein-vermittelte Vesikelfusion

PNA Hybrid Sequences as Recognition Units in SNARE-Protein-Mimicking Peptides

Membrane fusion is an essential process in nature and is often accomplished by the specific interaction of SNARE proteins. SNARE model systems, in which SNARE domains are replaced by small artificial units, represent valuable tools to study membrane fusion in vitro. The synthesis and analysis is presented of SNARE model peptides that exhibit a recognition motif composed of two different types of peptide nucleic acid (PNA) sequences. This novel recognition unit is designed to mimic the SNARE zippering mechanism that initiates SNARE-mediated fusion. It contains N-(2-aminoethyl)glycine-PNA (aeg-PNA) and alanyl-PNA, which both recognize the respective complementary strand but differ in duplex topology and duplex formation kinetics. The duplex formation of PNA hybrid oligomers as well as the fusogenicity of the model peptides in lipid-mixing assays were characterized and the peptides were found to induce liposome fusion. As an unexpected discovery, peptides with a recognition unit containing only five aeg-PNA nucleo amino acids were sufficient and most efficient to induce liposome fusion.

Supramolecular Control over Split-Luciferase Complementation

Supramolecular split-enzyme complementation restores enzymatic activity and allows for on-off switching. Split-luciferase fragment pairs were provided with an N-terminal FGG sequence and screened for complementation through host-guest binding to cucurbit[8]uril (Q8). Split-luciferase heterocomplex formation was induced in a Q8 concentration dependent manner, resulting in a 20-fold upregulation of luciferase activity. Supramolecular split-luciferase complementation was fully reversible, as revealed by using two types of Q8 inhibitors. Competition studies with the weak-binding FGG peptide revealed a 300-fold enhanced stability for the formation of the ternary heterocomplex compared to binding of two of the same fragments to Q8. Stochiometric binding by the potent inhibitor memantine could be used for repeated cycling of luciferase activation and deactivation in conjunction with Q8, providing a versatile module for in vitro supramolecular signaling networks.

Distance Regulated Vesicle Fusion and Docking Mediated by β-Peptide Nucleic Acid SNARE Protein Analogues

Artificial SNARE analogues derived from SNARE proteins, which mediate synaptic membrane fusion, are of interest. They mimic the tetrameric α-helix bundle of the SNARE motif with various bio-oligomer recognition units. Interaction between complementary oligomers linked to the respective membrane by lipid or peptide anchors leads to proximity of vesicles and to fusion of lipid bilayers. β-Peptide nucleic acids were introduced as hybrid oligomers with the native SNARE protein transmembrane/linker sequence, in order to evaluate a fusion system that allows distance tuning of approaching membranes. Formation of a four-base pair β-PNA double strand with 20 Å length is sufficient for vesicle membrane fusion. Elongation of the recognition β-PNA duplex in the linker region yielded a 40 Å β-peptide duplex and provided a vesicle-vesicle distance that only supported hemifusion of vesicle membranes.