Fig. 1: Electron microscopy of Ctpom152 reveals the assembly of beaded strings.

a Domain architecture of Ctpom152 and Hsgp210. Regions without a predicted fold are indicated in gray; Ig, immunoglobulin (Ig)-like fold; TM, transmembrane segment; pre-Ig, the conserved segment between TM and Ig1. See Supplementary Figs. S1, S2 for details. b Limited chymotryptic digestion of full-length (FL) recombinant Ctpom152. c Negative-stain EM of chymotryptic fragment showed beaded and flexible strings of ~40 nm in length (37 ± 4 nm, number of particles: N = 30); two of the beaded strings (two dashed boxes) are shown enlarged (orange, bottom inserts); up to ten beads are discernible. d SDS-PAGE and Coomassie Blue staining of purified recombinant Ctpom152^186-1270. e Like c, negative-stain EM of recombinant Ctpom152^186-1270 also showed beaded string structures (measures 40 ± 5 nm, N = 30). f SEC-MALS indicates that Ctpom152^186-1270 is a monomer. g–j Cryo-electron micrograph of Ctpom152^FL. g Single particle showed flexible beaded strings (measures 44 ± 3 nm, N = 30), as seen in negative-stain EM (c, e) and four selected particles (orange with dashed box) are enlarged (h). i Two selected particles with high contrast showing ten beads (indicated by arrow heads) and the large structural variations. j Ctpom152^FL polymerizes into long continuous strings with no punctuation marks. Particles represent the polymer formed by seven (bottom left), two (top), and five copies (right). k We speculate that (1) eight trans region of pom152 head-to-tail connect into a flexible ring and (2) two anti-parallel, stacked rings form above (cyan, omitted regions represented by dashed line), below (orange, omitted regions represented by dashed line), and mid-plane (black dashed line)