Fig. 1

GluA1 existed as monomers, homodimers, and homotrimers as well as homotetramers when expressed in the HEK293-PM. Note that most of the data about GluA2 are shown in the Supplementary Information. a Schematic figure showing the structures of ACP-GluA1, ACP-GluA1ΔNTD, ACP-GluA2, and ACP-TM. LBD represents the ligand-binding domain. Representative snapshot images and distributions (histograms) of the signal intensities of individual fluorescent spots of ATTO594-labeled ACP-TM (b) and ACP-GluA1 (c) expressed in HEK293-PMs. Distributions of the signal intensities of individual fluorescent spots (histograms) were obtained at various expression levels (number densities). The numbers of examined fluorescent spots: 779, 1729, and 2192 spots for ACP-TM (from left to right in b and 4305, 7730, and 7107 spots for ACP-GluA1 (from left to right in c). Each distribution was fitted with the sum of two (for ACP-TM, b) or four (for ACP-GluA1, c) lognormal functions, representing the fractions of monomers (magenta), homodimers (blue), homotrimers (green), and homotetramers (orange). Numbers in the figure indicate molecular fractions. Magenta arrowheads and yellow arrows in the images indicate spots with fluorescence intensities of <3.6 and >3.6 arbitrary units (A.U.). This threshold intensity was determined as that at which the ratio of the copy numbers of ACP-TM with higher vs. lower intensities in the experimental histogram became the same as the ratio of apparent dimers vs. monomers determined by the lognormal fitting. Related ACP-GluA2 results are shown in Supplementary Fig. 3b