Housing Aquaporins in Nanostructured Glass
Doktorsavhandling, 2019

Proteins are a group of biomolecules that perform versatile tasks, which in many cases are essential for life. The magnitude of their importance is perhaps expressed by the word protein itself, coined by the Swedish chemist Jöns Jacob Berzelius in the summer of 1838. It is derived from the Greek word πρωτείος which means ‘primary’ or ‘of the highest importance’. By adding a different ending, Berzelius shaped the word protein which means ‘the most important building block in a thin thread’.

The proteins of importance to this PhD thesis are aquaporins, whose primary function in nature is to sustain the osmotic balance across the cell membrane by transporting water. This transportation is highly energy efficient and selective compared to artificial processes, which renders aquaporins interesting from a water purification point of view. Many proteins, including aquaporins, are however not stable in non-native environments, which often results in protein degradation or aggregation upon use in synthetic environments. This is particularly prominent for membrane proteins, which need to be housed in an amphiphilic environment to function properly.

This thesis explores aquaporin stabilization through different kinds of interactions with glass. Human Aquaporin 4 was either intercalated with a mesoporous silica substrate or covered in a thin layer of silica. In both cases, aquaporins were stabilized by a lipid bilayer that mimics its native cell membrane surroundings. This thesis also includes work on the first structural and functional characterization of Climbing Perch Aquaporin 1 and a synthesis method for producing uniform silica nanoparticles with accessible mesopores.

Detailed characterization provided valuable information on different kinds of aquaporin-silica interactions. Aquaporins were, for instance, shown to extend into a porous silica substrate underneath a supported lipid bilayer. Furthermore, aquaporin secondary structure was preserved when stabilized by a silica shell. The findings in this thesis show that silica may be used as a biocompatible stabilization option for aquaporins, potentially paving the way for better aquaporin utilization in applications such as water purification.

Membrane protein

Water

Interface

Aquaporin

Silica

Formation

Silicification

KB-salen, Kemigården 4
Opponent: Prof. Duncan Sutherland, Interdisciplinary Nanoscience Center, Aarhus University, Denmark

Författare

Simon Isaksson

Chalmers, Kemi och kemiteknik, Tillämpad kemi, Martin Andersson Group

Mesoporous Silica Nanoparticles with Controllable Morphology Prepared from Oil-in-Water Emulsions

Journal of Colloid and Interface Science,; Vol. 467(2016)p. 253-260

Artikel i vetenskaplig tidskrift

Protein-Containing Lipid Bilayers Intercalated with Size-Matched Mesoporous Silica Thin Films

Nano Letters,; Vol. 17(2017)p. 476-485

Artikel i vetenskaplig tidskrift

Isaksson, S, Lotsari, A, Schmitz, F, Kjellerup Lind, T, Barnsley, L, Prevost, S, Hedfalk, K, Lund, R, Höök, F, Andersson, M. Formation Mechanism of Silica-Stabilized Aquaporin Proteoliposomes

Zeng, J, Schmitz, F, Isaksson, S, Arbab, O, Andersson, M, Törnroth-Horsefield, S, Swaminathan, K, Hedfalk, K. Novel structural mechanism of extracellular gating of aquaporin from the fish climbing perch (Anabas testudineus)

Tillgång till rent vatten är sedan 2010 en mänsklig rättighet enligt FN och självklart har det varit en nödvändighet mycket längre än så. Tillgång till rent vatten är dock ingen självklarhet varken för människor, djur eller växter ur ett globalt perspektiv vilket gjort att denna fråga inkluderats i de globala hållbarhetsmålen. Trots vattnets nyckelroll för liv är dagens vattenrening inte kapabel att hantera de ökande mängder och nya typer av föroreningar
som den ökande befolkningen och konsumtionen fört med sig. Vad kan vi göra åt detta?

Väldigt mycket, visar det sig. En viktig bit är att angripa källan till problemet genom att minska våra ekologiska fotavtryck och därmed minska tillförseln av föroreningar. En annan nyckel är att hitta hållbara sätt att rena vatten. Denna avhandling är en del i det utvecklingsarbete som jag och mina forskarkollegor bedrivit i jakt på hållbar vattenrening. Utvecklingen har skett med naturen som källa till både inspiration och komponenter.

Naturen renar vatten genom allt från storskalig avdunstning från världshaven till filtrering på cellnivå. Cellen kallas ibland livets minsta byggsten, men för att fungera behöver den ännu mindre byggstenar som exempelvis rent vatten. Selektiv och energieffektiv vattentransport in och ut ur cellen sköts av timglasformade kanaler som heter aquaporiner. Enbart vatten kan ta sig genom den smala passagen i timglaset och cellen renar på detta sätt vatten till låg energikostnad. Aquaporiner är av denna anledning högintressanta i vattenreningssyfte, men svåra att använda i praktiska tillämpningar på grund av dålig stabilitet i icke naturliga miljöer.

För att dra nytta av aquaporinens unika kombination av hög selektivitet och låg energikostnad inom vattenrening behövs stabilisering. Huvuddelen av denna avhandling utforskar därför hur glas kan användas för att stabilisera aquaporiner. Valet av kiseldioxid (huvudbeståndsdelen i glas) som stabiliseringsmaterial är inspirerat av vissa horn- och kiselsvampar samt kiselalger som använder just detta material för förstärkning. Resultaten av våra studier visar att aquaporiner kan stabiliseras med hjälp av kiseldioxid, vilket förhoppningsvis innebär ett betydande steg på vägen mot hållbar vattenrening.

Access to clean water is since 2010 considered a human right by the UN and it has obviously been a necessity for much longer than that. Access to clean drinking water is however not a given for neither humans, animals, nor plants in a global perspective and the UN has therefore introduced several targets on this topic in their Sustainable Development Goals (SDGs). Despite our vital dependency on water, current water treatment technologies struggle with new kinds of pollutants introduced as a consequence of an increase in population and consumption. What can we do about it?

Fortunately, a lot. One approach is to tackle the problem at its source by decreasing our ecological footprints to decrease pollution. Another important task is to find sustainable methods to purify water. This thesis is a part of the efforts made by me and my colleagues on our quest for sustainable water purification. We found both inspiration and potential purification components in nature.

In nature, water is purified on various length scales; from large-scale ocean evaporation to single-file water filtration across the cell membrane. Cells are sometimes referred to as “The building blocks of life”, but they require even smaller components to function. Water is one such component and it is selectively transported across the cell membrane through hourglass-shaped channels named aquaporins. Aquaporin proteins are selective enough to only allow water to cross the tight passage of the hourglass-shaped channel. This purification process allows the cell to purify water at minimal energy expense, which renders aquaporins interesting from a water purification point of view. Membrane proteins such as aquaporins are however difficult to use in applications due to their limited stability in non-native environments.

Stabilization is needed to make use of the unique potential that lies within the combination of excellent water selectivity and low energy consumption offered by these proteins. Silica, which is the main constituent of glass and very abundant in the Earth’s crust, fortifies certain siliceous sponges and diatoms in nature. These organisms acted as inspiration for this thesis, which explores how glass may be used in aquaporin stabilization. Our studies show that aquaporins may be stabilized by silica in ways that will hopefully make sustainable water purification become a reality.

Nanostrukturerade konstruktioner för vattenrening

Formas, 2013-01-01 -- 2016-12-31.

Drivkrafter

Hållbar utveckling

Innovation och entreprenörskap

Ämneskategorier

Biokemi och molekylärbiologi

Materialkemi

Biofysik

Strukturbiologi

Nanoteknik

Styrkeområden

Materialvetenskap

ISBN

978-91-7597-851-2

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4532

Utgivare

Chalmers tekniska högskola

KB-salen, Kemigården 4

Opponent: Prof. Duncan Sutherland, Interdisciplinary Nanoscience Center, Aarhus University, Denmark

Mer information

Senast uppdaterat

2019-02-28