Spermidine-Induced Attraction of Like-Charged Surfaces Is Correlated with the pH-Dependent Spermidine Charge: Force Spectroscopy Characterization.

Published

Journal Article

The ubiquitous molecule spermidine is known for its pivotal roles in the contact mediation, fusion, and reorganization of biological membranes and DNA. In our model system, borosilicate beads were attached to atomic force microscopy cantilevers and used to probe mica surfaces to study the details of the spermidine-induced attractions. The negative surface charges of both materials were largely constant over the measured pH range of pH 7.8 to 12. The repulsion observed between the surfaces turned into attraction after the addition of spermidine. The attractive force was correlated with the degree of spermidine protonation, which changed from +3 to +1 over the measured pH range. The force was maximal at pH 7.8. To explain the observed pH and spermidine concentration dependence, two different theoretical approaches were used: a chemical model of the charge equilibrium of spermidine and Monte-Carlo simulations of the orientation of the rodlike spermidine molecules in the gap between the borosilicate and mica surfaces. Monte-Carlo simulations of the orientational ordering of the rodlike spermidine molecules suggested the induction of attractive interactions between the surfaces if the gap was bridged by the molecules. For larger gaps, the orientational distribution function of the spermidine molecules predicted a considerable degree of parallel attachment of the molecules to the surfaces, resulting in reduced effective surface charge densities of both surfaces, which reduced their electrostatic repulsion.

Full Text

Duke Authors

Cited Authors

  • Gimsa, J; Wysotzki, P; Perutkova, Š; Weihe, T; Elter, P; Marszałek, P; Kralj-Iglič, V; Müller, T; Iglič, A

Published Date

  • February 15, 2018

Published In

Volume / Issue

  • 34 / 8

Start / End Page

  • 2725 - 2733

PubMed ID

  • 29382192

Pubmed Central ID

  • 29382192

Electronic International Standard Serial Number (EISSN)

  • 1520-5827

International Standard Serial Number (ISSN)

  • 0743-7463

Digital Object Identifier (DOI)

  • 10.1021/acs.langmuir.7b04199

Language

  • eng