Homologous Expression and Characterization of an LPMO from Commensal <i>Lactiplantibacillus plantarum</i> WCFS1 and Comparison with Related Enzymes from Chitin-Degrading Bacteria

High Resolution Image Download MS PowerPoint Slide Lytic polysaccharide monooxygenases (LPMOs) catalyze oxidative cleavage of glycosidic bonds and are important members of Nature’s enzymatic machinery for the deconstruction of recalcitrant polysaccharides. While chitin-active LPMOs are typically found in microorganisms that also produce chitinases, Lactiplantibacillus plantarum, a commensal lactic acid bacterium, lacks the chitinolytic machinery yet encodes a single-domain LPMO, hereinafter called Lp LPMO10A. Here, we characterize Lp LPMO10A produced both homologously and heterologously and demonstrate through structural modeling and sequence comparisons that it groups with canonical chitin-active LPMOs. Biochemical assays show that Lp LPMO10A catalyzes oxidative cleavage of chitin, producing C1-oxidized products. Analysis of productive (chitin peroxygenase reaction) and nonproductive (ascorbate peroxidase reaction) H 2 O 2 -consumption, together with additional functional assays, showed that Lp LPMO10A is very similar to Sm LPMO10A from Serratia marcescens, with a known role in chitin degradation. Moreover, Lp LPMO10A was more efficient in degrading chitin than Bl LPMO10A from Bacillus licheniformis, which harbors a chitinolytic gene repertoire including chitinases. For all three LPMOs, these activities showed only minor pH-dependence in the pH 5 – 7 range, meaning that Lp LPMO10A does not seem to have a particular potential to act at acidic pH. This lack of pH dependence is shared with fungal LPMOs despite the presence of different titratable groups in the second coordination sphere of the copper. While our results reveal functional variation among chitin-active bacterial LPMOs, for example regarding their ability to withstand oxidative damage, they do not identify distinct functional features that clarify the biological role of Lp LPMO10A. Taken together, our findings highlight Lp LPMO10A as an evolutionarily intriguing LPMO, namely a chitin-active enzyme retained in a nonchitinolytic bacterium.