4gwa | pdb_00004gwa
Crystal Structure of a GH7 Family Cellobiohydrolase from Limnoria quadripunctata
Structural highlights
FunctionGH7B_LIMQU Exocellobiohydrolase (CBH) that catalyzes the hydrolysis of 1,4-beta-D-glucosidic bonds in cellulose to release the disaccharide cellobiose (PubMed:23733951). The degradation of cellulose involves an interplay between different cellulolytic enzymes. Hydrolysis starts with endoglucanases (EGs), which cut internal beta-1,4-glucosidic bonds in cellulose to reduce the polymerization degree of the substrate and create new chain ends for exocellobiohydrolases (CBHs). The CBHs release the disaccharide cellobiose from the non-reducing end of the cellulose polymer chain. Finally, beta-1,4-glucosidases hydrolyze the cellobiose and other short cello-oligosaccharides into glucose units (Probable).[1] Publication Abstract from PubMedNature uses a diversity of glycoside hydrolase (GH) enzymes to convert polysaccharides to sugars. As lignocellulosic biomass deconstruction for biofuel production remains costly, natural GH diversity offers a starting point for developing industrial enzymes, and fungal GH family 7 (GH7) cellobiohydrolases, in particular, provide significant hydrolytic potential in industrial mixtures. Recently, GH7 enzymes have been found in other kingdoms of life besides fungi, including in animals and protists. Here, we describe the in vivo spatial expression distribution, properties, and structure of a unique endogenous GH7 cellulase from an animal, the marine wood borer Limnoria quadripunctata (LqCel7B). RT-quantitative PCR and Western blot studies show that LqCel7B is expressed in the hepatopancreas and secreted into the gut for wood degradation. We produced recombinant LqCel7B, with which we demonstrate that LqCel7B is a cellobiohydrolase and obtained four high-resolution crystal structures. Based on a crystallographic and computational comparison of LqCel7B to the well-characterized Hypocrea jecorina GH7 cellobiohydrolase, LqCel7B exhibits an extended substrate-binding motif at the tunnel entrance, which may aid in substrate acquisition and processivity. Interestingly, LqCel7B exhibits striking surface charges relative to fungal GH7 enzymes, which likely results from evolution in marine environments. We demonstrate that LqCel7B stability and activity remain unchanged, or increase at high salt concentration, and that the L. quadripunctata GH mixture generally contains cellulolytic enzymes with highly acidic surface charge compared with enzymes derived from terrestrial microbes. Overall, this study suggests that marine cellulases offer significant potential for utilization in high-solids industrial biomass conversion processes. Structural characterization of a unique marine animal family 7 cellobiohydrolase suggests a mechanism of cellulase salt tolerance.,Kern M, McGeehan JE, Streeter SD, Martin RN, Besser K, Elias L, Eborall W, Malyon GP, Payne CM, Himmel ME, Schnorr K, Beckham GT, Cragg SM, Bruce NC, McQueen-Mason SJ Proc Natl Acad Sci U S A. 2013 Jun 18;110(25):10189-94. doi:, 10.1073/pnas.1301502110. Epub 2013 Jun 3. PMID:23733951[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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