Figure 2. Sequence alignment, characteristics, and the model substrates of catalytic β-subunits from the c- and i-proteasome. Mature form sequences of human β1/β1i (A), β2/β2i (B), and β5/β5i (C) subunits are aligned using UniProt (https://www.uniprot.org/align/) and sequence similarities are rendered by ESPript 3.0 (https://espript.ibcp.fr/ESPript/ESPript/). Residue numbers are assigned based on the forms of the unprocessed (before autocatalytic cleavage). The percentage of amino acid identity and similarity between the cognate subunits is shown on the left. Similar residues are presented in yellow, identical residues in red, and key residues forming proteasomal catalytic triads (Thr1, Asp17, Lys33 after cleavage) are in green boxes. Potentially critical amino acid changes in S1 binding pockets, which could contribute to the substrate specificity of inducible βi subunits, are shown in blue boxes. Conventional fluorogenic peptide substrates are presented in red for c-proteasomes and in blue for i-proteasomes.