Structural basis for Atg8/LC3 processing and deconjugation. Top: Crystal structure of unprocessed rat LC3B (yellow) in a complex with human ATG4B (blue) harboring a Ser substitution in place of the catalytic Cys74 (here noted as Cys). The left view shows LC3B in the same orientation as in Figure 3, and the right shows ATG4B with a transparent surface, rotated 90° about the x-axis to provide a close-up view. The C-terminal LC3B residues including the penultimate Phe119, neo C-terminal Gly120, and pro sequence are shown in sticks, as are ATG4B's Cys-Asp-His of the catalytic triad (here the Cys is substituted with Ser) and Trp clamping down the LC3 C terminus. Bottom: schematic view of Atg4 functions, as illustrated with the S. cerevisiae Atg8 C-terminal sequence. Atg4 orthologs from other organisms display overall similar functions, including with Atg8 orthologs displaying different C-terminal sequences. The Atg12– Atg5-Atg16 conjugate is shown in its role as an E3 ligase for Atg8.