Abstract
A nanosensory membrane device was constructed for detecting liposome fusion through changes in an enzymatic activity. Inspired by a biological signal transduction system, the device design involved functionalized liposomal membranes prepared by self-assembly of the following molecular components: a synthetic peptide lipid and a phospholipid as matrix membrane components, a Schiff's base of pyridoxal 5′-phosphate with phosphatidylethanolamine as a thermo-responsive artificial receptor, NADH-dependent L-lactate dehydrogenase as a signal amplifier, and Cu2+ ion as a signal mediator between the receptor and enzyme. The enzymatic activity of the membrane device was adjustable by changing the matrix lipid composition, reflecting the thermotropic phase transition behavior of the lipid membranes, which in turn controlled receptor binding affinity toward the enzyme-inhibiting mediator species. When an effective fusogen anionic polymer was added to these cationic liposomes, membrane fusion occurred, and the functionalized liposomal membranes responded with changes in enzymatic activity, thus serving as an effective nanosensory device for liposome fusion detection.
Highlights
Much effort has been devoted to developing nanoscale devices using molecules or molecular devices composed of molecular elements, such as switches, wires, and logic gates, and capable of extending current semiconductor technology to nanoscale information technology [1,2,3,4].integration of these functional elements to produce real molecular devices still remains a challenge
We report an examination of this system’s enzymatic activity in response to various conditions and additives, adjustment of the system’s lipid composition while monitoring the phase transition temperature, and detection by the designed enzymatic response of phase transitions triggered by liposome fusion
A 1 mL sample solution was prepared by mixing lactate dehydrogenase (LDH) and NADH (2.8 nM and 0.25 mM, respectively) in the presence or absence of an appropriate amount of Cu2+ ions and liposomes, and the reaction initiated by addition of pyruvate (0.50 mM)
Summary
Much effort has been devoted to developing nanoscale devices using molecules or molecular devices composed of molecular elements, such as switches, wires, and logic gates, and capable of extending current semiconductor technology to nanoscale information technology [1,2,3,4]. We have previously reported here that a similar supramolecular system using receptor 3 and LDH markedly decreases enzymatic activity within a specific temperature range, reflecting the membrane's gel to liquid-crystalline phase transition [14]. This is due to increased mediator binding to the enzyme as a result of decreased mediator binding affinity toward the receptor. The present membrane device detects liposome fusion by translating the state change to an enzymatic response
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