Fig. 1.

Monomeric iECAM structure. (A) Domain organization of ECAM with spanning residues (see also SI Appendix, Fig. S7). A, flexible segment; BRD, bait-region domain; CUB, domain type first described in proteins C1r/C1s, Uegf, and Bmp1; L, linker; MG0–MG7, macroglobulin-type domains 0 to 7; NIE, N-terminal domain of induced ECAM; RBD, receptor-binding domain; SP, signal peptide; TED, thioester domain. The bait region and the thioester segment are depicted as green and purple handles, respectively. Red arrows pinpoint the primary trypsin cleavage sites for induction (R⁹⁴⁶) and solubilization/dimerization (R¹⁶²). Domain naming is based on hα₂M, which lacks A, MG0, and NIE (8). (B) Scheme of iECAM in front view. (C) Ribbon-plot of monomeric iECAM in front, lateral, and back views. In B and C, the domain colors are as in A, and the visible polypeptide chain ends upstream (U) and downstream (D) of the cleaved bait region, as well as the thioester (cyan ellipse; blown up in the inset in C), are indicated.