title: Exo-exo synergy between Cel6A and Cel7A from Hypocrea jecorina: Role of carbohydrate binding module and the endo-lytic character of the enzymes.
abstract: Synergy between cellulolytic enzymes is essential in both natural and industrial breakdown of biomass. In addition to synergy between endo- and exo-lytic enzymes, a lesser known but equally conspicuous synergy occurs among exo-acting, processive cellobiohydrolases (CBHs) such as Cel7A and Cel6A from Hypocrea jecorina. We studied this system using microcrystalline cellulose as substrate and found a degree of synergy between 1.3 and 2.2 depending on the experimental conditions. Synergy between enzyme variants without the carbohydrate binding module (CBM) and its linker was strongly reduced compared to the wild types. One plausible interpretation of this is that exo-exo synergy depends on the targeting role of the CBM. Many earlier works have proposed that exo-exo synergy was caused by an auxiliary endo-lytic activity of Cel6A. However, biochemical data from different assays suggested that the endo-lytic activity of both Cel6A and Cel7A were 103-104times lower than the common endoglucanase, Cel7B, from the same organism. Moreover, the endo-lytic activity of Cel7A was 2-3-fold higher than for Cel6A, and we suggest that endo-like activity of Cel6A cannot be the main cause for the observed synergy. Rather, we suggest the exo-exo synergy found here depends on different specificities of the enzymes possibly governed by their CBMs. Biotechnol. Bioeng. 2017;114: 1639-1647. © 2017 Wiley Periodicals, Inc.
authors.affiliation: Research Unit for Functional Biomaterials, Department of Science and Environment, INM, Roskilde University, 1 Universitetsvej, Build. 28C, DK-4000, Roskilde, Denmark.
authors.forename: Silke F
authors.identifier: 0000-0003-1127-0754
authors.initials: SF
authors.lastname: Badino
authors.affiliation: Research Unit for Functional Biomaterials, Department of Science and Environment, INM, Roskilde University, 1 Universitetsvej, Build. 28C, DK-4000, Roskilde, Denmark.
authors.forename: Stefan J
authors.identifier: 0000-0001-9164-2225
authors.initials: SJ
authors.lastname: Christensen
authors.affiliation: Research Unit for Functional Biomaterials, Department of Science and Environment, INM, Roskilde University, 1 Universitetsvej, Build. 28C, DK-4000, Roskilde, Denmark.
authors.forename: Jeppe
authors.identifier: 0000-0003-3792-3856
authors.initials: J
authors.lastname: Kari
authors.affiliation: Research Unit for Functional Biomaterials, Department of Science and Environment, INM, Roskilde University, 1 Universitetsvej, Build. 28C, DK-4000, Roskilde, Denmark.|Novozymes A/S, Bagsvaerd, Denmark.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Windahl
authors.affiliation: Research Unit for Functional Biomaterials, Department of Science and Environment, INM, Roskilde University, 1 Universitetsvej, Build. 28C, DK-4000, Roskilde, Denmark.
authors.forename: Søren
authors.identifier: 0000-0002-7315-3089
authors.initials: S
authors.lastname: Hvidt
authors.affiliation: Novozymes A/S, Bagsvaerd, Denmark.
authors.forename: Kim
authors.initials: K
authors.lastname: Borch
authors.affiliation: Research Unit for Functional Biomaterials, Department of Science and Environment, INM, Roskilde University, 1 Universitetsvej, Build. 28C, DK-4000, Roskilde, Denmark.
authors.forename: Peter
authors.identifier: 0000-0002-6185-0637
authors.initials: P
authors.lastname: Westh
mesh_terms: D001665:Binding Sites; D002482:Cellulose / Q000737:chemistry*; D004357:Drug Synergism; D004789:Enzyme Activation; D005656:Fungal Proteins / Q000737:chemistry*; D035901:Hypocrea / Q000201:enzymology*; D009097:Multienzyme Complexes; D011485:Protein Binding; D013379:Substrate Specificity
chemical_list: D005656:Fungal Proteins; D009097:Multienzyme Complexes; D002482:Cellulose; C109691:microcrystalline cellulose
keywords: CBM; Cel6A; Cel7A; cellobiohydrolase; cellulose; exo-exo synergy