title: Analysis of cellodextrin transporters from Neurospora crassa in Saccharomyces cerevisiae for cellobiose fermentation.
abstract: Saccharomyces cerevisiae can be engineered to ferment cellodextrins produced by cellulases as a product of cellulose hydrolysis. Direct fermentation of cellodextrins instead of glucose is advantageous because glucose inhibits cellulase activity and represses the fermentation of non-glucose sugars present in cellulosic hydrolyzates. To facilitate cellodextrin utilization by S. cerevisiae, a fungal cellodextrin-utilizing pathway from Neurospora crassa consisting of a cellodextrin transporter and a cellodextrin hydrolase has been introduced into S. cerevisiae. Two cellodextrin transporters (CDT-1 and CDT-2) were previously identified in N. crassa, but their kinetic properties and efficiency for cellobiose fermentation have not been studied in detail. In this study, CDT-1 and CDT-2, which are hypothesized to transport cellodextrin with distinct mechanisms, were introduced into S. cerevisiae along with an intracellular β-glucosidase (GH1-1). Cellobiose transport assays with the resulting strains indicated that CDT-1 is a proton symporter while CDT-2 is a simple facilitator. A strain expressing CDT-1 and GH1-1 (DCDT-1G) showed faster cellobiose fermentation than the strain expressing CDT-2 and GH1-1 (DCDT-2G) under various culture conditions with different medium compositions and aeration levels. While CDT-2 is expected to have energetic benefits, the expression levels and kinetic properties of CDT-1 in S. cerevisiae appears to be optimum for cellobiose fermentation. These results suggest CDT-1 is a more effective cellobiose transporter than CDT-2 for engineering S. cerevisiae to ferment cellobiose.
authors.affiliation: Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
authors.forename: Heejin
authors.initials: H
authors.lastname: Kim
authors.forename: Won-Heong
authors.initials: WH
authors.lastname: Lee
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Galazka
authors.forename: Jamie H D
authors.initials: JH
authors.lastname: Cate
authors.forename: Yong-Su
authors.initials: YS
authors.lastname: Jin
mesh_terms: D002475:Cellobiose / Q000378:metabolism*; D002482:Cellulose / Q000031:analogs & derivatives* / Q000378:metabolism; D003912:Dextrins / Q000378:metabolism*; D005285:Fermentation; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009492:Neurospora crassa / Q000201:enzymology* / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism
chemical_list: D003912:Dextrins; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins; D002475:Cellobiose; D002482:Cellulose; C068994:cellodextrin