Biochemistry

Breakdown Breakthrough

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Science  24 Jun 2011:
Vol. 332, Issue 6037, pp. 1483
DOI: 10.1126/science.332.6037.1483-c

Lignin is an organic polymer that binds tightly to cellulose fibers in plant cell walls, imparting rigidity and strength. The conversion of plant biomass into biofuels has been a challenge, in part because lignin hinders the degradation of cellulose into sugars that can be fermented. One approach is to use enzymes that break down lignin. Although such enzymes have been characterized in fungi, these microorganisms have been difficult to exploit commercially. Some bacteria secrete lignin-degrading enzymes, but the details are not well understood. The identification of a bacterial lignin-degrading gene would allow large-scale production of the enzyme in an organism that is easy to genetically manipulate and grow. Ahmad et al. used a bioinformatics approach to identify a gene in the soil bacterium Rhodococcus jostii that encodes a lignin-degrading peroxidase (DypB). In the presence of manganese salts, recombinant DypB expressed and purified from Escherichia coli showed degradation activity toward lignin, lignocelluloses from wheat straw, and synthetic model compounds. It is not clear how DypB is secreted from R. jostii, but the dypB gene is adjacent to a gene that encodes encapsulin, a shell-forming protein. The authors speculate that the genes may be coupled, and that an encapulsin nanocompartment could facilitate secretion.

Biochemistry 50, 5096 (2011).

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