Biology subjects

Florentsen, C. D.

Publications and source records attributed to Florentsen, C. D..

3 recordsLinked to original sources

bioRxiv2021

Annexin A4 senses membrane curvature in a density-dependent manner

Annexins (ANXs) are a family of peripheral membrane binding proteins which play a vital role in the maintenance and function of cellular membranes. These proteins are known to be part of the plasma membrane repair machinery where they are known to bind to negatively charged lipids in the cell membrane in a calcium dependent manner. The shape of the plasma membrane is known to be a regulator of protein density and thereby affects several biological functions of the cell such as exo-and endocytosis, cell motility, immune responses and also membrane repair. Membrane deformation and curvature sensing by proteins is a well described phenomenon which can assist in recruitment of specific proteins to certain regions in the cell and facilitate membrane bending. Following ruptures in the plasma membrane, calcium influx assist in the association of ANXs with the membrane around the ruptured area. Due to the expected increase in curvature at the damaged membrane site, it has been suggested that both membrane curvature and Ca2+ participate in the recruitment of ANXs. We have investigated the curvature sensing of ANXA4 in giant unilamellar vesicles (GUVs) by pulling high curvature membrane tethers from the vesicle surface using optical tweezers showing that ANXA4 recruitment increases with higher membrane curvature. We also describe an assay for determining protein density on the plasma membrane by utilizing ANXA4s property as a calcium dependent membrane binding protein. This new assay allows us to investigate the effect of protein density on curvature sensing.

biophysics↗

bioRxiv2021

Thermoplasmonic nano-rupture of cells reveals Annexin V function in plasma membrane repair

Maintaining the integrity of the cell plasma membrane (PM) is critical for the survival of cells. While an efficient PM repair machinery can aid survival of healthy cells by preventing influx of extracellular calcium, it can also constitute an obstacle in drug delivery and photothermal therapy. We show how nanoscopic holes can be applied to the cell surface thus allowing identification of molecular components with a pivotal role in PM repair. Cells are punctured by locally heating gold nanostructures at the cell surface which causes nano-ruptures in cellular PMs. Recruitment of annexin V near the hole is found to locally reshape the ruptured plasma membrane. Experiments using model membranes, containing recombinant annexin V, provide further biophysical insight into the ability of annexin V to reshape edges surrounding a membrane hole. The thermoplasmonic method provides a general strategy to monitor the response to nanoscopic injuries to the cell surface.

biophysics↗

bioRxiv2020

Annexin A4 trimers are recruited by high membrane curvatures in Giant Plasma Membrane Vesicles

The plasma membrane of eukaryotic cells consists of a crowded environment comprised of a high diversity of proteins in a complex lipid matrix. The lateral organization of membrane proteins in the plasma membrane (PM) is closely correlated with biological functions such as endocytosis, membrane budding and other processes which involve protein mediated shaping of the membrane into highly curved structures. Annexin A4 (ANXA4) is a prominent player in a number of biological functions including plasma membrane repair. Its binding to membranes is activated by Ca2+ influx and it is therefore rapidly recruited to the cell surface near rupture sites where Ca2+ influx takes place. However, the free edges near rupture sites can easily bend into complex curvatures and hence may accelerate recruitment of curvature sensing proteins to facilitate rapid membrane repair. To analyze the curvature sensing behavior of curvature inducing proteins in crowded membranes, we quantifify the affinity of ANXA4 monomers and trimers for high membrane curvatures by extracting membrane nanotubes from giant plasma membrane vesicles (GPMVs). ANXA4 is found to be a sensor of negative membrane curvatures. Multiscale simulations furthermore predicted that ANXA4 trimers generate membrane curvature upon binding and have an affinity for highly curved membrane regions only within a well defined membrane curvature window. Our results indicate that curvature sensing and mobility of ANXA4 depend on the trimer structure of ANXA4 which could provide new biophysical insight into the role of ANXA4 in membrane repair and other biological processes.

biophysics↗