Arrangement of Annexin A2 tetramer and its impact on the structure and diffusivity of supported lipid bilayers

Abstract

Annexins are a family of proteins that bind to anionic phospholipid membranes in a Ca 2+ -dependent manner. Annexin A2 forms heterotetramers (Anx A2t) with the S100A10 (p11) protein dimer. The tetramer is capable of bridging phospholipid membranes and it has been suggested to play a role in Ca 2+ -dependent exocytosis and cell-cell adhesion of metastatic cells. Here, we employ x-ray reflectivity measurements to resolve the conformation of Anx A2t upon Ca 2+ -dependent binding to single supported lipid bilayers (SLBs) composed of different mixtures of anionic (POPS) and neutral (POPC) phospholipids. Based on our results we propose that Anx A2t binds in a side-byside configuration, i.e., both Anx A2 monomers bind to the bilayer with the p11 dimer positioned on top. Furthermore, we observe a strong decrease of lipid mobility upon binding of Anx A2t to SLBs with varying POPS content. X-ray reflectivity measurements indicate that binding of Anx A2t also increases the density of the SLB. Interestingly, in the protein-facing leaflet of the SLB the lipid density is higher than in the substrate-facing leaflet. This asymmetric densification of the lipid bilayer by Anx A2t and Ca 2+ might have important implications for the biochemical mechanism of Anx A2t-induced endo-and exocytosis.

Label-free characterization of biomembranes: from structure to dynamics

“…6). It can also be used to look at the lipid bilayer underneath a bound protein 136,137 or bilayers coated with adsorbed polymers, investigate the location of a molecule within the bilayer, etc. There are detailed reviews of neutron reflectometry on lipid bilayers [137][138][139][140][141] and X-ray reflectometry and its applications to biological membranes at the solid-liquid interface.…”

Lipid Monolayer Formation and Lipid Exchange Monitored by a Graphene Field-Effect Transistor

“…Optical microscopy is per se insensitive to charged lipids; thus, fluorescence techniques rely on labeling techniques, that is, phosphoserine lipids (PS) can be imaged by labeling kits using binding of fluorescent annexins to PS via divalent Ca 2+ ions . Because these binding assays passivate the PS, there is a need for a label-free electrical readout.…”

“…For SGFET devices, g m is determined by the charge carrier mobility, the capacitance of the interface with the electrolyte and the device dimensions. Despite their proven applicability for biosensing, − organic field-effect transistors mostly have low mobility, up to several dozen cm 2 /V s in best cases. Some organic materials, in particular PEDOT:PSS, show a huge effective capacitance, which compensates the low mobility at the cost of the response time, which is limited to the kHz region and requires carefully designed geometries to achieve ms resolution. , Lipid membranes on PEDOT:PSS hinder ion diffusion which further slow down the performance of PEDOT:PSS-based transistors .…”

“…23 Optical microscopy is per se insensitive to charged lipids; thus, fluorescence techniques rely on labeling techniques, that is, phosphoserine lipids (PS) can be imaged by labeling kits using binding of fluorescent annexins to PS via divalent Ca 2+ ions. 24 Because these binding assays passivate the PS, there is a need for a label-free electrical readout. Label-free detection reduces both complexity and cost of the experiments, as well as it excludes any possible influence of a dye on the outcome of a measurement.…”

Annexin A2 is not a good biomarker for hepatocellular carcinoma in cirrhosis

“…Annexin A2 (ANXA2), a member of the annexin family, is involved in various biological functions including cell-cell adhesion (6), cell proliferation (7,8), cell surface fibrinolysis (9,10), cell growth regulation and apoptosis (11–13) and the cocarcinogenic effects of progastrin (14). It has been reported that ANXA2 is frequently upregulated in HCC patients compared with controls (15,16), suggesting that ANXA2 is associated with HCC.…”