Kari Kristine Almåsvold

• Koynarev, Vladimir Rosenov; Nader, Manuela Leal; Borgos, Kari Kristine Almåsvold; Cezar, Henrique Musseli; Narayanan, Theyencheri & Porcar, Lionel [Show all 8 contributors for this article] (2025). Structural pores not required: Antimicrobial peptides induce ion permeabilization of lipid membranes through transient water channels. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 122(44). doi: 10.1073/pnas.2517944122. Full text in Research Archive Show summary

  Antimicrobial peptides (AMPs) are highly potent and broad-spectrum antibiotics, found as components of the innate immune system in almost all forms of life. Despite being commonly accepted that the mechanism of action of AMPs is associated with the permeabilization of the cell membrane, the structural and dynamical means by which this occurs are still heavily debated. In this work, we employ experimental time-resolved small angle X-ray scattering to follow in real time the AMP-induced ion transport in lipid vesicles, while simultaneously resolving the membrane structure and peptide partitioning. For several natural AMPs, we show that they can effectively permeabilize the lipid membrane despite only binding peripherally to the outer membrane leaflet. Our experiments reveal rapid ion transport associated with AMP binding, yielding salt equilibration in a few tens of milliseconds, while not detecting evidence of transversal and structurally stable peptide pores. On the contrary, new analysis of previously reported all-atom molecular dynamics simulations shows that lipid flip-flop, accelerated by the peripherally bound peptides, leads to the formation of transient, ion-conducting water channels. A corresponding diffusional model indicates that such short-lived, transient pores explain the observed ion transport better than stable pores.

• Cárdenas, Marité; Bjørnestad, Victoria Ariel; Borgos, Kari Kristine Almåsvold & Lund, Reidar (2025). The integrity of the lipid bilayer structure is retained in natural occurring deep eutectic solvent water mixtures - a small angle X-ray scattering study. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 27(10248), p. 10258–10258. doi: 10.1039/d5cp00331h. Full text in Research Archive Show summary

  Natural occurring deep eutectic solvents (NADES) are solvents made of metabolites occurring in living organisms, and are thought to play a special role in plants especially given that some of these metabolites exist in concentrations as high as 1 M. NADES have properties similar to ionic liquids, and have been shown to protect enzymes against loss of activity as well as proteins against thermal denaturation. Here, we explore the structure of lipid vesicles in NADES rich aqueous solutions and compare to concentrated saline aqueous solutions matching the various NADES osmolarity. The vesicle structure was analysed by small angle X-ray scattering (SAXS) and dynamic light scattering (DLS). Two types of NADES were prepared using choline chloride and glucose or maleic acid at a molar ratio of 1 : 1 giving the solvents a neutral or an acidic nature, respectively. The stability of the vesicles in the various solvents was measured against time and temperature. The results of this work demonstrate that lipid bilayers retain their structure in NADES rich aqueous solutions as compared to pure water, in contrast to high saline aqueous solutions. Moreover, the vesicles are more stable against sedimentation and aggregation in NADES than in water.

• Koynarev, Vladimir Rosenov; Borgos, Kari Kristine Almåsvold; Kohlbrecher, Joachim; Porcar, Lionel; Nielsen, Josefine Eilsø & Lund, Reidar (2024). Antimicrobial Peptides Increase Line Tension in Raft-Forming Lipid Membranes. Journal of the American Chemical Society. ISSN 0002-7863. 146(30), p. 20891–20903. doi: 10.1021/jacs.4c05377. Full text in Research Archive Show summary

  The formation of phase separated membrane domains is believed to be essential for the function of the cell. The precise composition and physical properties of lipid bilayer domains play crucial roles in regulating protein activity and governing cellular processes. Perturbation of the domain structure in human cells can be related to neurodegenerative diseases and cancer. Lipid rafts are also believed to be essential in bacteria, potentially serving as targets for antibiotics. An important question is how the membrane domain structure is affected by bioactive and therapeutic molecules, such as surface-active peptides, which target cellular membranes. Here we focus on antimicrobial peptides (AMPs), crucial components of the innate immune system, to gain insights into their interaction with model lipid membranes containing domains. Using small-angle neutron/X-ray scattering (SANS/SAXS), we show that the addition of several natural AMPs (indolicidin, LL-37, magainin II, and aurein 2.2) causes substantial growth and restructuring of the domains, which corresponds to increased line tension. Contrast variation SANS and SAXS results demonstrate that the peptide inserts evenly in both phases, and the increased line tension can be related to preferential and concentration dependent thinning of the unsaturated membrane phase. We speculate that the lateral restructuring caused by the AMPs may have important consequences in affecting physiological functions of real cells. This work thus shines important light onto the complex interactions and lateral (re)organization in lipid membranes, which is relevant for a molecular understanding of diseases and the action of antibiotics.

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