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LIPIDSTRUCT: LIpids, DIsorder and STRUCTure

Function and dysfunction of flexible, membrane-binding proteins

A large part of the highly organized and compartmentalized eukaryotic cell genomes code for proteins that are dynamic, disordered and flexible yet still functional. Many of these are involved in regulated and/or transient interaction with lipid membranes in the cell, such as the outer cell membrane, nucleus membrane, mitochondria and other organelles. Such systems – based on protein amphitropism – are very important to life, but knowledge lags behind what we know of the soluble, ordered proteins. The fundamental goal of the research group is thus to understand how protein-membrane interaction and protein disorder in general is used in the functional requirements of the cell, to understand what can go wrong, and whether these mechanisms can be exploited, e.g. in the development of new classes of drugs. We use liquid-state NMR, fluorescence and circular dichroism in combination with different model lipid membranes to explore such systems. We also work with surface Plasmon resonance and other biophysical techniques, as well as cultured cells for testing the effect of new constructs on these.

Main content

Protein disorder/structure and amphitropism are important in many phenomena that are under intensive scrutiny. These phenomena include:

i) Interactions between proteins and lipid membranes and how this is regulated is important for cytoskeleton motility, sustaining a high level of membrane organization, and in understanding the action of toxic protein multimers that again are interesting from a medical perspective.

ii) Protein folding and misfolding. This is an intrinsically interesting problem, but also one of high relevance for medical research. Many diseases have links to misfolding behaviour, such as Alzheimers, prionic diseases and other afflictions.

iii) Cellular signalling. Protein flexibility and dynamics are central to cellular signalling and especially for the one-to-many protein interactions that have been found to be particularly relevant for higher eukaryotic life.

 

The group’s main current experimental focus is the study of novel protein-based anti-cancer therapeutics involving disordered protein state, membrane interaction and lipid biochemistry. HAMLET – Human Alpha-Lactalbumin Made Lethal to Tumors – is a phenomenon in cancer research that has made for both an intrinsically interesting and clinically promising story. HAMLET was discovered in 1995, purified and characterized from a milk-fraction; the active component turned out to be a partially folded form of α-Lactalbumin with several oleic acid bound. It is of great fundamental interest to find out more about how the partially denaturated protein attains its lethality relative to its rather innocent native counterpart. The anti-cancer activity appear to be related to the enhanced surface activity of HAMLET, which in turn may be involved in efficiently stabilizing protein states that aggregates and efficiently compromises the cellular membrane. The interplay between the oleic acids, the folding and aggregation state of the protein, and the membrane thus forms an interesting multifaceted study with biomedical implications.

At present, the group collaborates (co-supervised students and joint publications) with several research groups on projects where amphitropism and protein disorder plays a role:

i) Biorecognition/Prof. Aurora Martínez/University of Bergen (UiB): 14-3-3g, Tyrosine Hydroxylase and the synaptic cellular membrane forms a tripartite interaction system that has implications for catecholamine synthesis and distribution. We’ve indentified a 14-3-3 isoform-specific function where a disordered segment on the N-terminal interact with 14-3-3g, which results in an increased affinity for a synaptic membrane mimic for the complex as a whole.

ii) Wilhelm Glomm/Norwegian University of Science and Technology (NTNU): Protein-membrane interactions as a general phenomenon is a special case of polymer interface chemistry. With Glomm’s group, we study how proteins can interact with and become immobilized on nano-particles. We observe that protein-nanoparticle constructs often have elevated surface activity, and that this can be modulated by controlling protein-surface interactions. An important aspect of this is knowing to what degree the protein unfolds at the interface, its orientation and its packing.  

iii) Nathalie Reuter/Computational Biology Unit (UiB): Nathalie Reuter/Computational Biology Unit (UiB): The interaction of PR3 -- a membrane-associated serine protease -- with the cellular membrane has been studied by MD simulations. This has revealed a number of previously inaccessible details, including interaction site and specific pairwise bonding between protein and lipid moieties. We explore these aspects of PR3-membrane binding with biophysical techniques.

iv) Gro Vang Amdam/State University of Arizona and University of Life Sciences (UMB): Vitellogenin, a large egg-yolk protein involved in reproduction, has been co-opted in honey bees to also have a role in managing behaviour and life-span of individual bees in the complex hive-society. We study the structural basis for this, and have identified functional disordered regions.

The group is newly established, and currently consists of the group leader, as well as one PhD-student (Hanzhen Wen), one master student (Ida Rundgren), and a technician (Anne Elisabeth Sandvik Madsen, part-time). The group leader co-supervises 4 other PhD-students in collaboration with UMB, NTNU and CBU and Department of Biomedicine, both at UiB (Biorecognition) (See above). Experimental focus includes protein structural determination by NMR, spectroscopic techniques (NMR, fluorescence and CD, as well as some mass-spectroscopy), lipid- and membrane chemistry (preparation of vesicles, bicelles and other lipid aggregates), and interfacial chemistry and physical techniques (e.g. Surface Plasmon Resonance, DLS).