Nanoscale Investigation of Generation 1 PAMAM Dendrimers Interaction with a Protein Nanopore

Alina Asandei,Aurelia Apetrei,Loredana Mereuta,Tudor Luchian,Irina Schiopu,Andrei Ciuca,Chang Ho Seo,Yoonkyung Park

doi:10.1038/s41598-017-06435-1

Alina Asandei, Aurelia Apetrei + Show 6 more

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https://doi.org/10.1038/s41598-017-06435-1

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Abstract

Herein, we describe at uni-molecular level the interactions between poly(amidoamine) (PAMAM) dendrimers of generation 1 and the α-hemolysin protein nanopore, at acidic and neutral pH, and ionic strengths of 0.5 M and 1 M KCl, via single-molecule electrical recordings. The results indicate that kinetics of dendrimer-α-hemolysin reversible interactions is faster at neutral as compared to acidic pH, and we propose as a putative explanation the fine interplay among conformational and rigidity changes on the dendrimer structure, and the ionization state of the dendrimer and the α-hemolysin. From the analysis of the dendrimer’s residence time inside the nanopore, we posit that the pH- and salt-dependent, long-range electrostatic interactions experienced by the dendrimer inside the ion-selective α-hemolysin, induce a non-Stokesian diffusive behavior of the analyte inside the nanopore. We also show that the ability of dendrimer molecules to adapt their structure to nanoscopic spaces, and control the flow of matter through the α-hemolysin nanopore, depends non-trivially on the pH- and salt-induced conformational changes of the dendrimer.

Highlights

Dendrimers possess remarkable structural flexibility, which is advantageous when seeking to achieve reproducible and predictable responsiveness to chemical, biological, or physical stimuli
At pH = 3 (Fig. 1, panel a), the trans-added dendrimer interacts with the positive charges at the β-barrel lumen opening, and inside the α-HL it interacts with the positively charged residues from its Q(cti ooF→Dnen l=ss,tp ra+iurce8rt|pireoel−nep|ar,(eraqsrnceoodnnwstit)rte.. d=iAna t+testr6h aF→.ic5eslt|,sper−Haetd|t,)rtaahacrnertdiocvwoven.elysAsttwtirb iipctu→Hhtlieot =hnde o7amnn(eFdagiivganet.sis1v(t,eqibpveuealsenlt.ec =etzlr o+bicn)2,ce8thah|aerere−gdde|e)eno4v6ndo. rTit→dihhmeoeesfβree-hblreeaacprstruraeillcsciaoavlplecceuhenllaaienrtcgegtedr(4oq6bs.ratiAanrgtes i=cschh i−noat7rweg|rneea−ioc|n-)f Fig. 1, panels a and b, the electrophoretic ( Felp) and electro-osmotic forces ( Felo) act oppositely on the dendrimer, at both pH’s
They are reduced in magnitude at neutral as compared to acidic pH, as the charged state of the dendrimer is smaller at pH = 7 than at pH = 3, and the anionic selectivity of the nanopore, which determines the net solvent velocity across the nanopore, is less prevalent in neutral as compared to acidic buffers

Summary

Introduction

Dendrimers possess remarkable structural flexibility, which is advantageous when seeking to achieve reproducible and predictable responsiveness to chemical, biological, or physical stimuli. As proven by SAXS16 and SANS17 experiments, the radius of gyration of various generations of the PAMAM dendrimers was found pH dependent, www.nature.com/scientificreports/. In accord with acidic pH-induced repulsion between dendritic branches or dendrimer back-folding at pH > 9, respectively[4, 18]. These findings were supported by coarse-grained[19, 20] and atomistic simulations[18, 21, 22]. The pH dependence of dendrimer size, conformation and mobility inside nanoscale volumes, as opposed to the bulk solution (vide supra), is key for the utilization of PAMAM dendrimers as biomolecule delivery vehicles in physiological environments with nanopores

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