A novel cell permeability assay for macromolecules
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(2020) 21:75
BMC Molecular and Cell Biology
METHODOLOGY ARTICLE
Open Access
A novel cell permeability assay for macromolecules Yensi Flores Bueso1,2,3, Sidney Walker1,2,3, Jennifer Quinn1 and Mark Tangney1,2,3*
Abstract Background: Many cell permeabilisation methods to mediate internalisation of various molecules to mammalian or bacterial cells have been developed. However, no size-specific permeability assay suitable for both cell types exists. Results: We report the use of intrinsically biotinylated cell components as the target for reporter molecules for assessing permeabilisation. Due to its well-described biotin binding activity, we developed an assay using Streptavidin (SAv) as a molecular weight marker for assessing eukaryotic and prokaryotic cell internalisation, using flow cytometry as a readout. This concept was tested here as part of the development of host DNA depletion strategies for microbiome analysis of formalin-fixed (FF) samples. Host depletion (HD) strategies require differential cell permeabilisation, where mammalian cells but not bacterial cells are permeabilised, and are subsequently treated with a nuclease. Here, the internalisation of a SAv-conjugate was used as a reference for nucleases of similar dimensions. With this assay, it was possible to demonstrate that formalin fixation does not generate pores which allow the introduction of 60 KDa molecules in mammalian or bacterial membranes/envelopes. Among surfactants tested, Saponin derived from Quillaja bark showed the best selectivity for mammalian cell permeabilisation, which, when coupled with Benzonase nuclease, provided the best results for host DNA depletion, representing a new HD strategy for formalin fixed samples. Conclusion: The assay presented provides researchers with a sensitive and accessible tool for discerning membrane/cell envelop permeability for different size macromolecules. Keywords: Cell permeabilisation, Biotin-streptavidin, In vitro labelling, MW marker, Host DNA depletion
Background The role that different macromolecules play within the cellular milieu is routinely studied with in vitro techniques that involve their ex vitro modification (labelling) and subsequent cellular internalisation [1]. Since the membrane of live mammalian cells is virtually impermeable against polar and charged molecules with a molecular weight (MW) larger than ~ 118 Da [2, 3], and the outer membrane of Gram-negative (G-) bacteria is only permeable to hydrophilic molecules smaller than ~ 600 Da [4], the internalisation of biomolecules must be * Correspondence: [email protected] 1 CancerResearch@UCC, University College Cork, Cork, Ireland 2 SynBioCentre, University College Cork, Cork, Ireland Full list of author information is available at the end of the article
artificially induced. For in vitro studies, this is achieved by permeabilising the cell membrane/envelope [5]. A plethora of permeabilisation methods have been developed for mammalian cells [6], and to a lesser extent for bacteria [7], including solvents (Alcohol, acetone), deterg
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