Short Cationic Peptides Induce PH-Sensitive Non-Leaky Membrane Fusion

Membrane fusion is a key process in all living cells.Enveloped viruses import their genomes into cells by fusion of their membrane coats with cell membrane,fertilization of sexually reproducing organisms also relies on the membrane fusion of sperm and egg cells,and intracellular fusion reactions in exocytosis,protein trafficking,and mitochondrial remodeling.Therefore,the studies on membrane fusion,especially its molecular mechanism,is a topic of great concern.To achieve fusion,energetic barriers associated with bringing opposing membranes together and subsequent membrane destabilization and merging must be overcome.In biological systems,these barriers are believed to be overcome by the presence of membrane fusion proteins.For many fusion proteins evidence now suggests that a triggered conformational change that exposes a previously cryptic fusion peptide,along with a rearrangement of the fusion protein,allows the fusion peptide to gain access to the target bilayer and thus initiate the fusion reaction.Fusion peptides are short,relatively hydrophobic sequences,which can induce membrane fusion as fusion protein.There is no doubt that membrane fusion has an overarching influence on living organisms.Considering its importance,surprisingly little is known about the molecular-level mechanism of membrane fusion.Due to the complexity of a living cell,observations often leave room for ambiguity in interpretation.Therefore artificial model systems composed of only a few components are being used to further our understanding of fusion processes.In this case,simple fusion peptide is obviously a better choice than complex fusion protein.Many studies on the mechanism of biological membrane fusion employ fusogenic peptides derived from natural proteins like influenza hemagglutinin.And in model systems,the synthetic peptide GALA,composed of repeating units of glutamic acid-alanine-leucine-alanine,is one of the most widely studied fusogens.However,compared with fusion protein,a drawback of most peptide fusogens is that membrane fusion is accompanied by a significant amount of leakage of the liposome contents.In particularly,studies on the construction of membrane fusion systems can be developed into advanced drug delivery and gene transfer.The pH-sensitive GALA induces membrane leaky fusion,which can help destroy cell membranes and even kill cells.However,not all treatments need to destroy cell membranes,such as gene transport.As we all know,destroying the integrity of cell membrane will lead to cell necrosis,releasing intracellular substances and thus causing inflammation.Therefore,we need non-leaky fusion polypeptides whether to explore the fusion mechanism of fusion proteins or to find the non-leaky fusion peptides needed for drug delivery.In this work,we report on non-leaky,pH-sensitive,complete fusion mediated by two short peptides,ORB-KK(LKGCWTKSIPPKPCFK,stabilized by one intra-molecular disulfide bond,hairpin-like peptide)and its open form(ORB-KKopen),which are analogues of ORB,an antimicrobial peptide secreted by skin of Odorranagrahami frog.To our knowledge,there are no reports on them in the literature.