Tania Lind | University of Copenhagen (original) (raw)

Papers by Tania Lind

Biochimica et Biophysica Acta (BBA) - Biomembranes, 2015

ABSTRACT The interaction mechanism of a novel amphiphilic antimicrobial peptide dendrimer, BALY, ... more ABSTRACT The interaction mechanism of a novel amphiphilic antimicrobial peptide dendrimer, BALY, with model lipid bilayers was explored through a combination of neutron reflection and molecular dynamics simulations. 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dipalmitoyl-sn-glycero-3-phos-phocholine (DPPC) lipid bilayers were examined at room temperature to extract information on the interaction of BALY with fluid and gel phases, respectively. Furthermore, a 1:4 mixture of POPC and DPPC was used as a model of a phase-separated membrane. Upon interaction with fluid membranes, BALY inserted in the distal leaflet and caused thinning and disordering of the headgroups. Membrane thinning and expansion of the lipid cross-sectional area was observed for gel phase membranes, also with limited insertion to the distal leaflet. However, dendrimer insertion through the entire lipid tail region was observed upon crossing the lipid phase transition temperature of DPPC and in phase separated membranes. The results show clear differences in the interaction mechanism of the dendrimer depending on the lipid membrane fluidity, and suggest that a role for lipid phase separation in promoting its antimicrobial activity. Copyright © 2015. Published by Elsevier B.V.

Molecules, 2015

Antimicrobial drug resistance is a major human health threat. Among the many attempts to tackle t... more Antimicrobial drug resistance is a major human health threat. Among the many attempts to tackle this problem, the synthesis of antimicrobial compounds that mimic natural antimicrobial peptides appears as a promising approach. Peptide-based dendrimers can be designed to have higher potency than natural antimicrobial peptides and at the same time they can evade the bacterial defense system. Novel dendrimers with similar chemical structure but varying potency in terms of minimum inhibitory concentration were designed. The dependency between dendrimer structure and antibacterial activity as well as their capacity to attack model cell membranes was studied. The data suggests that supramolecular structure in terms of charge distribution and amphiphilicity, rather than net charge, is the main driver for disruption of cellular membranes and this correlates well with dendrimer hemolytic activity.

Langmuir, 2014

We have investigated the effect of deposition temperature on supported lipid bilayer formation vi... more We have investigated the effect of deposition temperature on supported lipid bilayer formation via vesicle fusion. By using several complementary surface-sensitive techniques, we demonstrate that despite contradicting literature on the subject, high-quality bilayers can be formed below the main phase-transition temperature of the lipid. We have carefully studied the formation mechanism of supported DPPC bilayers below and above the lipid melting temperature (T m ) by quartz crystal microbalance and atomic force microscopy under continuous flow conditions. We also measured the structure of lipid bilayers formed below or above T m by neutron reflection and investigated the effect of subsequent cooling to below the T m . Our results clearly show that a continuous supported bilayer can be formed with high surface coverage below the lipid T m . We also demonstrate that the high dissipation responses observed during the deposition process by QCM-D correspond to vesicles absorbed on top of a continuous bilayer and not to a surface-supported vesicular layer as previously reported. A dx.doi.org/10.1021/la500897x | Langmuir XXXX, XXX, XXX−XXX ■ REFERENCES (1) Eeman, M.; Deleu, M. From biological membranes to biomimetic model membranes. Biotechnol. Agron. Soc. 2010, 14, 719−736. Langmuir Letter dx.doi.org/10.1021/la500897x | Langmuir XXXX, XXX, XXX−XXX D

Soft Matter, 2013

Soluble proteins in the extracellular matrix experience a crowded environment. However, most of t... more Soluble proteins in the extracellular matrix experience a crowded environment. However, most of the biophysical studies performed to date have focused on protein concentrations within the dilute regime (well below the mM range). Here, we systematically studied the interaction of model cell membrane systems (giant unilamellar vesicles and supported lipid bilayers) with soluble globular proteins, bovine serum albumin, hemoglobin and lysozyme at physiologically relevant concentrations. To mimic the extracellular environment more closely, we also used fetal bovine serum as a good representative of a biomimetic protein mixture. We found that regardless of the protein used (and thus of their biological function), the interactions between a model cell membrane and these proteins are determined by their physico-chemical characteristics, mainly their dipolar character (or charged patches). In this paper we discuss the specificity and reversibility of these interactions and their potential implications on the living cells. In particular, we report initial evidence for an additional role of glycolipids in cell membranes: that of reducing the effects of non-specific adsorption of soluble proteins on the cell membrane.

Langmuir, 2012

Poly(amidoamine) (PAMAM) dendrimers are promising candidates in several applications within the m... more Poly(amidoamine) (PAMAM) dendrimers are promising candidates in several applications within the medical field. However, it is still to date not fully understood whether they are able to passively translocate across lipid bilayers. Recently, we used fluorescence microscopy to show that PAMAM dendrimers induced changes in the permeability of lipid membranes but the dendrimers themselves could not translocate to be released into the vesicle lumen. Because of the lack of resolution, these experiments could not assess whether the dendrimers were able to translocate but remained attached to the membrane. Using quartz crystal microbalance with dissipation monitoring and neutron reflectivity, a structural investigation was performed to determine how dendrimers interact with zwitterionic and negatively charged lipid bilayers. We hereby show that dendrimers adsorb on top of lipid bilayers without significant dendrimer translocation, regardless of the lipid membrane surface charge. Thus, most likely dendrimers are actively transported through cell membranes by protein-mediated endocytosis in agreement with previous cell studies. Finally, the higher activity of PAMAM dendrimers for phosphoglycerolcontaining membranes is in line with their high antimicrobial activity against Gram-negative bacteria.

ACS Nano, 2014

In this paper, an amphiphilic peptide dendrimer with potential applications against multi-resista... more In this paper, an amphiphilic peptide dendrimer with potential applications against multi-resistant bacteria such as Staphylococcus aureus was synthesized and studied on model cell membranes. The combination of quartz crystal microbalance and atomic force microscopy imaging during continuous flow allowed for in situ monitoring of the very initial interaction processes and membrane transformations on longer time scales. We used three different membrane compositions of low and high melting temperature phospholipids to vary the membrane properties from a single fluid phase to a pure gel phase, while crossing the phase coexistence boundaries at room temperature. The interaction mechanism of the dendrimer was found to be time-dependent and to vary remarkably with the fluidity and coexistence of liquidÀsolid phases in the membrane. Spherical micelle-like dendrimerÀlipid aggregates were formed in the fluid-phase bilayer and led to partial solubilization of the membrane, while in gel-phase membranes, the dendrimers caused areas of local depressions followed by redeposition of flexible lipid patches. Domain coexistence led to a sequence of events initiated by the formation of a ribbon-like network and followed by membrane solubilization via spherical aggregates from the edges of bilayer patches. Our results show that the dendrimer molecules were able to destroy the membrane integrity through different mechanisms depending on the lipid phase and morphology and shed light on their antimicrobial activity. These findings could have an impact on the efficacy of the dendrimers since lipid membranes in certain bacteria have transition temperatures very close to the host body temperature.

Soft Matter, 2012

In this paper we present a systematic study of the morphology and composition of supported lipid ... more In this paper we present a systematic study of the morphology and composition of supported lipid bilayers (SLBs) formed by vesicle fusion using a wide variety of surface sensitive techniques that give information about the lateral as well as vertical structure and bilayer fluidity. SLBs of 1-palmitoyl-2oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixtures at five different bulk vesicle compositions were formed in such a way that the phase separation boundaries were crossed. For all compositions studied, the SLBs were systematically enriched with POPC compared to the nominal vesicle composition. Nevertheless, gel-fluid domain coexistence was observed for SLB compositions in which phase separation was expected based on the bulk phase diagram. The probable causes for the compositional difference in the SLBs are discussed in terms of the phase behaviour of the mixture and its effect on the membrane formation process by vesicle fusion.

Biochimica et Biophysica Acta (BBA) - Biomembranes, 2015

ABSTRACT The interaction mechanism of a novel amphiphilic antimicrobial peptide dendrimer, BALY, ... more ABSTRACT The interaction mechanism of a novel amphiphilic antimicrobial peptide dendrimer, BALY, with model lipid bilayers was explored through a combination of neutron reflection and molecular dynamics simulations. 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dipalmitoyl-sn-glycero-3-phos-phocholine (DPPC) lipid bilayers were examined at room temperature to extract information on the interaction of BALY with fluid and gel phases, respectively. Furthermore, a 1:4 mixture of POPC and DPPC was used as a model of a phase-separated membrane. Upon interaction with fluid membranes, BALY inserted in the distal leaflet and caused thinning and disordering of the headgroups. Membrane thinning and expansion of the lipid cross-sectional area was observed for gel phase membranes, also with limited insertion to the distal leaflet. However, dendrimer insertion through the entire lipid tail region was observed upon crossing the lipid phase transition temperature of DPPC and in phase separated membranes. The results show clear differences in the interaction mechanism of the dendrimer depending on the lipid membrane fluidity, and suggest that a role for lipid phase separation in promoting its antimicrobial activity. Copyright © 2015. Published by Elsevier B.V.

Molecules, 2015

Antimicrobial drug resistance is a major human health threat. Among the many attempts to tackle t... more Antimicrobial drug resistance is a major human health threat. Among the many attempts to tackle this problem, the synthesis of antimicrobial compounds that mimic natural antimicrobial peptides appears as a promising approach. Peptide-based dendrimers can be designed to have higher potency than natural antimicrobial peptides and at the same time they can evade the bacterial defense system. Novel dendrimers with similar chemical structure but varying potency in terms of minimum inhibitory concentration were designed. The dependency between dendrimer structure and antibacterial activity as well as their capacity to attack model cell membranes was studied. The data suggests that supramolecular structure in terms of charge distribution and amphiphilicity, rather than net charge, is the main driver for disruption of cellular membranes and this correlates well with dendrimer hemolytic activity.

Langmuir, 2014

We have investigated the effect of deposition temperature on supported lipid bilayer formation vi... more We have investigated the effect of deposition temperature on supported lipid bilayer formation via vesicle fusion. By using several complementary surface-sensitive techniques, we demonstrate that despite contradicting literature on the subject, high-quality bilayers can be formed below the main phase-transition temperature of the lipid. We have carefully studied the formation mechanism of supported DPPC bilayers below and above the lipid melting temperature (T m ) by quartz crystal microbalance and atomic force microscopy under continuous flow conditions. We also measured the structure of lipid bilayers formed below or above T m by neutron reflection and investigated the effect of subsequent cooling to below the T m . Our results clearly show that a continuous supported bilayer can be formed with high surface coverage below the lipid T m . We also demonstrate that the high dissipation responses observed during the deposition process by QCM-D correspond to vesicles absorbed on top of a continuous bilayer and not to a surface-supported vesicular layer as previously reported. A dx.doi.org/10.1021/la500897x | Langmuir XXXX, XXX, XXX−XXX ■ REFERENCES (1) Eeman, M.; Deleu, M. From biological membranes to biomimetic model membranes. Biotechnol. Agron. Soc. 2010, 14, 719−736. Langmuir Letter dx.doi.org/10.1021/la500897x | Langmuir XXXX, XXX, XXX−XXX D

Soft Matter, 2013

Soluble proteins in the extracellular matrix experience a crowded environment. However, most of t... more Soluble proteins in the extracellular matrix experience a crowded environment. However, most of the biophysical studies performed to date have focused on protein concentrations within the dilute regime (well below the mM range). Here, we systematically studied the interaction of model cell membrane systems (giant unilamellar vesicles and supported lipid bilayers) with soluble globular proteins, bovine serum albumin, hemoglobin and lysozyme at physiologically relevant concentrations. To mimic the extracellular environment more closely, we also used fetal bovine serum as a good representative of a biomimetic protein mixture. We found that regardless of the protein used (and thus of their biological function), the interactions between a model cell membrane and these proteins are determined by their physico-chemical characteristics, mainly their dipolar character (or charged patches). In this paper we discuss the specificity and reversibility of these interactions and their potential implications on the living cells. In particular, we report initial evidence for an additional role of glycolipids in cell membranes: that of reducing the effects of non-specific adsorption of soluble proteins on the cell membrane.

Langmuir, 2012

Poly(amidoamine) (PAMAM) dendrimers are promising candidates in several applications within the m... more Poly(amidoamine) (PAMAM) dendrimers are promising candidates in several applications within the medical field. However, it is still to date not fully understood whether they are able to passively translocate across lipid bilayers. Recently, we used fluorescence microscopy to show that PAMAM dendrimers induced changes in the permeability of lipid membranes but the dendrimers themselves could not translocate to be released into the vesicle lumen. Because of the lack of resolution, these experiments could not assess whether the dendrimers were able to translocate but remained attached to the membrane. Using quartz crystal microbalance with dissipation monitoring and neutron reflectivity, a structural investigation was performed to determine how dendrimers interact with zwitterionic and negatively charged lipid bilayers. We hereby show that dendrimers adsorb on top of lipid bilayers without significant dendrimer translocation, regardless of the lipid membrane surface charge. Thus, most likely dendrimers are actively transported through cell membranes by protein-mediated endocytosis in agreement with previous cell studies. Finally, the higher activity of PAMAM dendrimers for phosphoglycerolcontaining membranes is in line with their high antimicrobial activity against Gram-negative bacteria.

ACS Nano, 2014

In this paper, an amphiphilic peptide dendrimer with potential applications against multi-resista... more In this paper, an amphiphilic peptide dendrimer with potential applications against multi-resistant bacteria such as Staphylococcus aureus was synthesized and studied on model cell membranes. The combination of quartz crystal microbalance and atomic force microscopy imaging during continuous flow allowed for in situ monitoring of the very initial interaction processes and membrane transformations on longer time scales. We used three different membrane compositions of low and high melting temperature phospholipids to vary the membrane properties from a single fluid phase to a pure gel phase, while crossing the phase coexistence boundaries at room temperature. The interaction mechanism of the dendrimer was found to be time-dependent and to vary remarkably with the fluidity and coexistence of liquidÀsolid phases in the membrane. Spherical micelle-like dendrimerÀlipid aggregates were formed in the fluid-phase bilayer and led to partial solubilization of the membrane, while in gel-phase membranes, the dendrimers caused areas of local depressions followed by redeposition of flexible lipid patches. Domain coexistence led to a sequence of events initiated by the formation of a ribbon-like network and followed by membrane solubilization via spherical aggregates from the edges of bilayer patches. Our results show that the dendrimer molecules were able to destroy the membrane integrity through different mechanisms depending on the lipid phase and morphology and shed light on their antimicrobial activity. These findings could have an impact on the efficacy of the dendrimers since lipid membranes in certain bacteria have transition temperatures very close to the host body temperature.

Soft Matter, 2012

In this paper we present a systematic study of the morphology and composition of supported lipid ... more In this paper we present a systematic study of the morphology and composition of supported lipid bilayers (SLBs) formed by vesicle fusion using a wide variety of surface sensitive techniques that give information about the lateral as well as vertical structure and bilayer fluidity. SLBs of 1-palmitoyl-2oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixtures at five different bulk vesicle compositions were formed in such a way that the phase separation boundaries were crossed. For all compositions studied, the SLBs were systematically enriched with POPC compared to the nominal vesicle composition. Nevertheless, gel-fluid domain coexistence was observed for SLB compositions in which phase separation was expected based on the bulk phase diagram. The probable causes for the compositional difference in the SLBs are discussed in terms of the phase behaviour of the mixture and its effect on the membrane formation process by vesicle fusion.