title: The binding of cellulase variants to dislocations: a semi-quantitative analysis based on CLSM (confocal laser scanning microscopy) images.
abstract: Binding of enzymes to the substrate is the first step in enzymatic hydrolysis of lignocellulose, a key process within biorefining. During this process elongated plant cells such as fibers and tracheids have been found to break into segments at irregular cell wall regions known as dislocations or slip planes. Here we study whether cellulases bind to dislocations to a higher extent than to the surrounding cell wall. The binding of fluorescently labelled cellobiohydrolases and endoglucanases to filter paper fibers was investigated using confocal laser scanning microscopy and a ratiometric method was developed to assess and quantify the abundance of the binding of cellulases to dislocations as compared to the surrounding cell wall. Only Humicola insolens EGV was found to have stronger binding preference to dislocations than to the surrounding cell wall, while no difference in binding affinity was seen for any of the other cellulose variants included in the study (H. insolens EGV variants, Trichoderma reesei CBHI, CBHII and EGII). This result favours the hypothesis that fibers break at dislocations during the initial phase of hydrolysis mostly due to mechanical failure rather than as a result of faster degradation at these locations.
authors.affiliation: UniBio a/s, Billedskaerervej 8, 5230, Odense M, Denmark. bjh@unibio.dk.
authors.forename: Budi J
authors.initials: BJ
authors.lastname: Hidayat
authors.affiliation: Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Am Műhlenberg 1, Potsdam, 14476, Germany. Carmen.Weisskopf@mpikg.mpg.de.
authors.forename: Carmen
authors.initials: C
authors.lastname: Weisskopf
authors.affiliation: Department of Geosciences and Natural Resource Management, University of Copenhagen, Rolighedsvej 23, 1958, Frederiksberg, Denmark. cf@ign.ku.dk.
authors.forename: Claus
authors.initials: C
authors.lastname: Felby
authors.affiliation: Division of Industrial Biotechnology, Chalmers University of Technology, Kemivägen 10, 41296, Göteborg, Sweden. skatja@chalmers.se.
authors.forename: Katja S
authors.initials: KS
authors.lastname: Johansen
authors.affiliation: Department of Geosciences and Natural Resource Management, University of Copenhagen, Rolighedsvej 23, 1958, Frederiksberg, Denmark. lgt@ign.ku.dk.
authors.forename: Lisbeth G
authors.initials: LG
authors.lastname: Thygesen
keywords: Cellulase binding; Confocal laser scanning microscopy; Dislocations; Fluorescence-labelled enzymes; Ratio imaging; Semi-quantitative analysis