Single Molecule Measurements of the Accessibility of Molecular Surfaces

An important measure of the conformation of protein molecules is the degree of surface exposure of its specific segments. However, this is hard to measure at the level of individual molecules. Here, we combine single molecule photobleaching (smPB, which resolves individual photobleaching steps of si...

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Autores principales:	Arpan Dey, Vicky Vishvakarma, Anirban Das, Mamata Kallianpur, Simli Dey, Roshni Joseph, Sudipta Maiti
Formato:	article
Lenguaje:	EN
Publicado:	Frontiers Media S.A. 2021
Materias:	single molecule conformation single molecule photobleaching single molecule quenching SASA hIAPP (human islet amyloid polypeptide) Biology (General) QH301-705.5
Acceso en línea:	https://doaj.org/article/e8a795d137e14dd88dd70d1288ebdee3
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spelling	oai:doaj.org-article:e8a795d137e14dd88dd70d1288ebdee32021-12-02T00:25:02ZSingle Molecule Measurements of the Accessibility of Molecular Surfaces2296-889X10.3389/fmolb.2021.745313https://doaj.org/article/e8a795d137e14dd88dd70d1288ebdee32021-12-01T00:00:00Zhttps://www.frontiersin.org/articles/10.3389/fmolb.2021.745313/fullhttps://doaj.org/toc/2296-889XAn important measure of the conformation of protein molecules is the degree of surface exposure of its specific segments. However, this is hard to measure at the level of individual molecules. Here, we combine single molecule photobleaching (smPB, which resolves individual photobleaching steps of single molecules) and fluorescence quenching techniques to measure the accessibility of individual fluorescently labeled protein molecules to quencher molecules in solution. A quencher can reduce the time a fluorophore spends in the excited state, increasing its photostability under continuous irradiation. Consequently, the photo-bleaching step length would increase, providing a measure for the accessibility of the fluorophore to the solvent. We demonstrate the method by measuring the bleaching step-length increase in a lipid, and also in a lipid-anchored peptide (both labelled with rhodamine-B and attached to supported lipid bilayers). The fluorophores in both molecules are expected to be solvent-exposed. They show a near two-fold increase in the step length upon incubation with 5 mM tryptophan (a quencher of rhodamine-B), validating our approach. A population distribution plot of step lengths before and after addition of tryptophan show that the increase is not always homogenous. Indeed there are different species present with differential levels of exposure. We then apply this technique to determine the solvent exposure of membrane-attached N-terminus labelled amylin (h-IAPP, an amyloid associated with Type II diabetes) whose interaction with lipid bilayers is poorly understood. hIAPP shows a much smaller increase of the step length, signifying a lower level of solvent exposure of its N-terminus. Analysis of results from individual molecules and step length distribution reveal that there are at least two different conformers of amylin in the lipid bilayer. Our results show that our method (“Q-SLIP”, Quenching-induced Step Length increase in Photobleaching) provides a simple route to probe the conformational states of membrane proteins at a single molecule level.Arpan DeyVicky VishvakarmaAnirban DasMamata KallianpurSimli DeyRoshni JosephSudipta MaitiFrontiers Media S.A.articlesingle molecule conformationsingle molecule photobleachingsingle molecule quenchingSASAhIAPP (human islet amyloid polypeptide)Biology (General)QH301-705.5ENFrontiers in Molecular Biosciences, Vol 8 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	single molecule conformation single molecule photobleaching single molecule quenching SASA hIAPP (human islet amyloid polypeptide) Biology (General) QH301-705.5
spellingShingle	single molecule conformation single molecule photobleaching single molecule quenching SASA hIAPP (human islet amyloid polypeptide) Biology (General) QH301-705.5 Arpan Dey Vicky Vishvakarma Anirban Das Mamata Kallianpur Simli Dey Roshni Joseph Sudipta Maiti Single Molecule Measurements of the Accessibility of Molecular Surfaces
description	An important measure of the conformation of protein molecules is the degree of surface exposure of its specific segments. However, this is hard to measure at the level of individual molecules. Here, we combine single molecule photobleaching (smPB, which resolves individual photobleaching steps of single molecules) and fluorescence quenching techniques to measure the accessibility of individual fluorescently labeled protein molecules to quencher molecules in solution. A quencher can reduce the time a fluorophore spends in the excited state, increasing its photostability under continuous irradiation. Consequently, the photo-bleaching step length would increase, providing a measure for the accessibility of the fluorophore to the solvent. We demonstrate the method by measuring the bleaching step-length increase in a lipid, and also in a lipid-anchored peptide (both labelled with rhodamine-B and attached to supported lipid bilayers). The fluorophores in both molecules are expected to be solvent-exposed. They show a near two-fold increase in the step length upon incubation with 5 mM tryptophan (a quencher of rhodamine-B), validating our approach. A population distribution plot of step lengths before and after addition of tryptophan show that the increase is not always homogenous. Indeed there are different species present with differential levels of exposure. We then apply this technique to determine the solvent exposure of membrane-attached N-terminus labelled amylin (h-IAPP, an amyloid associated with Type II diabetes) whose interaction with lipid bilayers is poorly understood. hIAPP shows a much smaller increase of the step length, signifying a lower level of solvent exposure of its N-terminus. Analysis of results from individual molecules and step length distribution reveal that there are at least two different conformers of amylin in the lipid bilayer. Our results show that our method (“Q-SLIP”, Quenching-induced Step Length increase in Photobleaching) provides a simple route to probe the conformational states of membrane proteins at a single molecule level.
format	article
author	Arpan Dey Vicky Vishvakarma Anirban Das Mamata Kallianpur Simli Dey Roshni Joseph Sudipta Maiti
author_facet	Arpan Dey Vicky Vishvakarma Anirban Das Mamata Kallianpur Simli Dey Roshni Joseph Sudipta Maiti
author_sort	Arpan Dey
title	Single Molecule Measurements of the Accessibility of Molecular Surfaces
title_short	Single Molecule Measurements of the Accessibility of Molecular Surfaces
title_full	Single Molecule Measurements of the Accessibility of Molecular Surfaces
title_fullStr	Single Molecule Measurements of the Accessibility of Molecular Surfaces
title_full_unstemmed	Single Molecule Measurements of the Accessibility of Molecular Surfaces
title_sort	single molecule measurements of the accessibility of molecular surfaces
publisher	Frontiers Media S.A.
publishDate	2021
url	https://doaj.org/article/e8a795d137e14dd88dd70d1288ebdee3
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Single Molecule Measurements of the Accessibility of Molecular Surfaces

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