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Differential Effect of Bilayer Thickness on Sticholysin Activity

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Palacios Ortega, Juan and García Linares, Sara and Rivera de la Torre, Esperanza and Gavilanes, José G. and Martínez del Pozo, Álvaro and Slotte, J. Peter (2017) Differential Effect of Bilayer Thickness on Sticholysin Activity. Langmuir, 33 (41). pp. 11018-11027. ISSN 0743-7463(Print) 1520-5827 (On line)

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Official URL: http://pubs.acs.org/doi/abs/10.1021%2Facs.langmuir.7b01765



Abstract

In this study, we examined the influence of bilayer thickness on the activity of the actinoporin toxins sticholysin I and II (StnI and StnII) at 25 °C. Bilayer thickness was varied using dimonounsaturated phosphatidylcholine (PC) analogues (with 14:1, 16:1, 18:1, 20:1, and 22:1 acyl chains). In addition, N-14:0-sphingomyelin (SM) was always included because StnI and StnII are SM specific. Cholesterol was also incorporated as indicated. In cholesterol-free large unilamellar vesicles (LUVs) the PC:SM molar ratio was 4:1, and when cholesterol was included, the complete molar ratio was 4:1:0.5 (PC:SM:cholesterol, respectively). Stn toxins promote bilayer leakage through pores formed by oligomerized toxin monomers. Initial calcein leakage was moderately dependent on bilayer PC acyl chain length (and thus bilayer thickness), with higher rates observed with di-16:1 and di-18:1 PC bilayers. In the presence of cholesterol, the maximum rates of calcein leakage were observed in di-14:1 and di-16:1 PC bilayers. Using isothermal titration calorimetry to study the Stn−LUV interaction, we observed that the bilayer affinity constant (Ka) peaked with LUVs containing di-18:1 PC, and was lower in shorter and longer PC acyl chain bilayers. The presence of cholesterol increased the binding affinity approximately 30-fold at the optimal bilayer thickness (di-18:1-PC). We conclude that bilayer thickness affects both functional and conformational aspects of Stn membrane binding and pore formation. Moreover, the length of the actinoporins’ N-terminal α-helix, which penetrates the membrane to form a functional pore, appears to be optimal for the membrane thickness represented by di-18:1 PC.


Item Type:Article
Subjects:Sciences > Chemistry > Molecular biology
Sciences > Chemistry > Biochemistry
ID Code:45297
Deposited On:31 Oct 2017 12:40
Last Modified:02 Nov 2017 08:30

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