Membrane affinity and fluorescent labelling: comparative study of monolayer interaction, cellular uptake and cytotoxicity profile of carboxyfluorescein-conjugated cationic peptides
Fluorescent labelling is a common approach to reveal the molecular details of cellular uptake, internalisation, transport, distribution processes in biological systems. The conjugation with a fluorescent moiety might affect relevant physico-chemical and in vitro transport properties of the bioactive component. A representative set of seven cationic peptides—including cell-penetrating peptides as well as antimicrobial peptides and synthetic derivatives—was selected for our comparative study. Membrane affinity of the peptides and their 5(6)-carboxyfluorescein (Cf) derivatives was determined quantitatively and compared applying Langmuir monolayer of zwitterionic (DPPC) and negatively charged (DPPC + DPPG) lipids as cell membrane models. The interaction with neutral lipid layer is mainly governed by the overall hydrophobicity of the molecule which is remarkably increased by Cf-conjugation for the most hydrophobic Magainin, Melittin and Transportan. A significantly enhanced membrane affinity was detected in negatively charged lipid model monolayer for all of the peptides since the combination of electrostatic and hydrophobic interaction is active in that case. The Cf-conjugation improved the penetration ability of Penetratin and Dhvar4 suggesting that both the highly charged character (Z/n) and the increased hydrophobicity by Cf-conjugation present important contribution to membrane interaction. This effect might also responsible for the observed high in vitro internalisation rate of Penetratin and Dhvar4, while according to in vitro studies they did not cause damage of cell membrane. From the experiments with the given seven cationic peptides, it can be concluded that the Cf-conjugation alters the degree of membrane interaction of such peptides which are moderately hydrophobic and highly charged.
KeywordsFluorescent labelling Membrane affinity Cell-penetrating peptides Lipid monolayer Penetration Cellular uptake
Valuable assistance of Mrs. I. Hórvölgyi and H. Szatmári in Langmuir experiments is acknowledged. This work was financially supported by National Research Development and Innovation Office, Hungary (OTKA 104275, 115431, 124077) and VEKOP-2.3.2-16-2017-00014 European Union and the State of Hungary, co-financed by the European Regional Development Fund. K. Horváti was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences. G. Gyulai was supported by the Hungarian Academy of Sciences Postdoctoral Research Program.
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Conflict of interest
The authors declare that they have no conflict of interest.
Research involving human participants and/or animals
This article does not contain any studies with human participants or animals performed by any of the authors.
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