Understanding Enzymes that Help Convert Biomass to Biofuels
A key step in the production of biofuels from biomass is hydrolytic breakdown of cellulose, a major component of all plants, into simple, fermentable sugars. Many natural systems carry out this breakdown, and much research is devoted to find systems that are highly efficient and thus candidates for inclusion in a biofuel production system. A new study of a subfamily of glucosidase enzymes (6-P-β-glucosidases), critical to
efficient hydrolysis of cellulose, uses x-ray crystallography to determine their structures and how they bind to cellulose molecules. The researchers isolated these enzymes from two bacteria commonly found in the digestive tracts of many mammals, including humans: Lactobacillus plantarum and Streptococcus mutans. They obtained structures of the enzymes alone and bound to key cellulose breakdown molecules, using the Structural Biology Center’s stations at Argonne National Laboratory’s Advanced Photon Source. Different bacteria show different
P-β-glucosidase and P-β-galactosidase activities. The structures and functional studies enabled the scientists to define structural features shared by glucosidases and galactosidases and those that are unique to the 6-P-β-glucosidases subfamily. Both enzymes show hydrolytic activity against 6’-P-β-glucosides but exhibit surprisingly different kinetic properties and affinities for substrates. Considering the conservation of the overall structures and active sites of various 6-P-β-glucosidases, the differences at their ligand binding subsites and the entrance to the active site are likely the determinants of their substrate specificities. These new findings will help scientists studying the design of efficient enzyme systems for biofuel production and will also have implications for human health.
Michalska, K., K. Tan, H. Li, C. Hatzos-Skintges, J. Bearden, G. Babnigg, and A. Joachimiak. 2013.
“GH1-Family 6-P-ß-Glucosidases from Human Microbiome Lactic Acid Bacteria,” Acta Crystallographica Section D: Biological Crystallography 69, 451–63. DOI:10.1107/S0907444912049608.