Crystal structure of exo-rhamnogalacturonan lyase from Penicillium chrysogenum as a member of polysaccharide lyase family 26

: Exo-rhamnogalacturonan lyase from Penicillium chrysogenum 31B (PcRGLX) was recently classified as a member of polysaccharide lyase (PL) family 26 along with hypothetical proteins derived from various organisms. In this study, we determined the crystal structure of PcRGLX as the first structure of a member of this family. Based on the substrate-binding orientation and substrate specificity, PcRGLX is an exo-type PL that cleaves rhamnogalacturonan from the reducing end. Analysis of PcRGLX-complex structures with reaction products indicate that the active site possesses an L-shaped cleft that can accommodate galactosyl side chains, suggesting side-chain-bypassing activity in PcRGLX. Furthermore, we determined the residues critical for catalysis by analyzing the enzyme activities of inactive variants.