Fig. 3: A5 2D-lattice growth alters the characteristics of the underlying lipid membrane.
From: Annexin-V stabilizes membrane defects by inducing lipid phase transition
a HS-AFM image frames (Supplementary Movie 2) showing the efficient formation of a supported lipid bilayer (SLB) membrane on mica through vesicle adsorption and spreading (white dashed outlined) and patch fusion (green dashed rectangles). b In the absence of additional vesicles deposited from buffer, the fusion of two small membrane patches can produce a new larger membrane patch that has freedom in surface diffusivity (Supplementary Movie 3). Right graph panel: movement estimated by mass center displacement through fusion process and surface diffusion. c HS-AFM image sequence from a longer HS-AFM movie (acquisition speed: 1 s per frame, Supplementary Movie 4) showing membrane-patch size decrease during A5 adsorption, self-assembly, and 2D-lattice growth. Yellow arrows indicate fast-diffusive, small A5 aggregates. d Time-lapse analysis of area and the number of A5 arrays (minimum size ≥ 200 nm2). Red arrows indicate the time of representative HS-AFM frames shown in c. Based on the changes in membrane area, A5 coverage, and A5-aggregate number, five distinct periods during the A5 self-assembly process are identified as following: (1) membrane shrinkage upon A5 addition, (2) A5 self-assembly into small A5 aggregates, (3) abundant A5 adsorption and coalescence of A5 aggregates in a large-scale 2D-lattice, (4) growth of a 2D-lattice until the membrane was fully covered, and (5) a solid A5-protective membrane. The assigned periods in d are labeled in the top-right corner of corresponding images in c. e Time-lapse analysis of mean height above the mica plane of the membrane patch and A5 aggregates. Each data point is the difference between centers Gaussian fits of the height distributions of the mica, the membrane, and the A5 with the error bar determined by the peak width of the Gaussian fit of the membrane/A5 height distribution (Supplementary Fig. 1). The thickness of bare membrane and A5-covered membrane are 3.15 ± 0.2 nm and 6.1 ± 0.2 nm, respectively. The A5 self-assembly process promotes an average membrane thickness increase to 3.35 ± 0.2 nm and 3.45 ± 0.3 nm during period (2) and (3), respectively. Detailed comparison among height histograms is provided in Supplementary Fig. 1.
