Fig. 2
From: Cryo-EM structures of the pore-forming A subunit from the Yersinia entomophaga ABC toxin
Chitinases in the context of the pre-pore structure. a Two unmodelled subdomains form the major interacting surface between YenA1 and Chi2: an insertion into the YenA1 α-helical shell (YenA1305–583) and the N-terminal domain of Chi2 (Chi21–91). A secondary interaction surface involves the α-helical shell (α1) from the neighbouring protomer (YenA1′). b The Chi2 active site (magenta) sits at the bottom of a downward facing substrate cleft. The Chi1 subunit could not be accommodated within any of the unbuilt regions of the final, high resolution map (Fig. 1) but densities that corresponded in size to the Chi1 crystal structure (PDB ID 3oa5) were resolved in maps produced during earlier refinement iterations (c; X-ray structures coloured in pink and fitted as a rigid body) and were also clearly evident in reference-free class averages (d; pink arrowheads)
