Construction of a bio-inspired signal transduction system: Activation of lactate dehydrogenase triggered by lipid signal molecules on bilayer vesicles

An artificial signal transduction system, in which an enzymatic activity was controlled by a lipid signal embedded in a biomembrane model, was constructed. The system was inspired by the biological phosphoinositide (PI)-triggered signal transduction. For this propose, hybrid bilayer vesicles with a mean diameter of 100 nm were formed by combination of dimyristylphosphatidylethanolamine as a lipid signal moiety and a cationic synthetic lipid as a matrix. The aggregate morphology was confirmed by means of transmission electron microscopy and dynamic light scatting measurements, and the vesicles showed a phase transition from gel to liquid-crystalline state at 31.2 degreesC as evaluated with differential scanning calorimetry. On the cationic vesicular surface, the lipid signal specifically recognized pyridoxal 5'-phosphate as a signal activator to form a signal-signal activator complex. The hydrophobic and the electrostatic interactions were much enhanced in the microenvironment on the vesicular surface to form the binary complex. The resulting binary complex exhibited extremely high binding affinity toward Cu2+ ions. Thus, the catalytic activity of lactate dehydrogenase, which was inhibited by binding of Cu2+ ion to the enzyme active site on bilayer vesicles, was effectively recovered upon formation of the signal-signal activator complex, reflecting that the binding affinity of the signal-signal activator complex with Cu2+ ion overcame that of the enzyme.