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Amyloid-Type Fiber Formation in Control of Enzyme Action: Interfacial Activation of Phospholipase A₂

Christian Code ^*, Yegor Domanov ^*, Arimatti Jutila ^* and Paavo K. J. Kinnunen ^* 

^* Helsinki Biophysics and Biomembrane Group, Medical Biochemistry, Institute of Biomedicine, University of Helsinki, Finland; and MEMPHYS Center for Biomembrane Physics, Physics Department, University of Southern Denmark, Odense, Denmark

Correspondence: Address reprint requests to Dr. Paavo K. J. Kinnunen, Helsinki Biophysics and Biomembrane Group, Medical Biochemistry, Institute of Biomedicine, University of Helsinki, P.O. Box 63 (Haartmaninkatu 8), FIN-00014. E-mail: Finland.paavo.kinnunen{at}helsinki.fi.

The lag-burst behavior in the action of phospholipase A₂ (PLA₂) on 1,2-dipalmitoyl-sn-glycero-3-phosphocholine was investigated at temperatures slightly offset from the main phase transition temperature T_m of this lipid, thus slowing down the kinetics of the activation process. Distinct stages leading to maximal activity were resolved using a combination of fluorescence parameters, including Förster resonance energy transfer between donor- and acceptor-labeled enzyme, fluorescence anisotropy, and lifetime, as well as thioflavin T fluorescence enhancement. We showed that the interfacial activation of PLA₂, evident after the preceding lag phase, coincides with the formation of oligomers staining with thioflavin T and subsequently with Congo red. Based on previous studies and our findings here, we propose a novel mechanism for the control of PLA₂, involving amyloid protofibrils with highly augmented enzymatic activity. Subsequently, these protofibrils form "mature" fibrils, devoid of activity. Accordingly, the process of amyloid formation is used as an on-off switch to obtain a transient burst in enzymatic catalysis.