cellulase and resorufin

There currently exists a diverse array of molecular probes for the in situ localization of polysaccharides, nucleic acids, and proteins in plant cells, including reporter enzyme strategies (e.g. protein-glucuronidase fusions). In contrast, however, there is a paucity of methods for the direct analysis of endogenous glycoside hydrolases and transglycosidases responsible for cell wall remodeling. To exemplify the potential of fluorogenic resorufin glycosides to address this issue, a resorufin beta-glycoside of a xylogluco-oligosaccharide (XXXG-beta-Res) was synthesized as a specific substrate for in planta analysis of XEH activity. The resorufin aglycone is particularly distinguished for high sensitivity in muro assays due to a low pK(a) (5.8) and large extinction coefficient (epsilon 62,000 M(-1) cm(-1)), long-wavelength fluorescence (excitation 571 nm/emission 585 nm), and high quantum yield (0.74) of the corresponding anion. In vitro analyses demonstrated that XXXG-beta-Res is hydrolyzed by the archetypal plant XEH, nasturtium (Tropaeolum majus) NXG1, with classical Michaelis-Menten substrate saturation kinetics and a linear dependence on both enzyme concentration and incubation time. Further, XEH activity could be visualized in real time by observing the localized increase in fluorescence in germinating nasturtium seeds and Arabidopsis (Arabidopsis thaliana) inflorescent stems by confocal microscopy. Importantly, this new in situ XEH assay provides an essential complement to the in situ xyloglucan endotransglycosylase assay, thus allowing delineation of the disparate activities encoded by xyloglucan endotransglycosylase/hydrolase genes directly in plant tissues. The observation that XXXG-beta-Res is also hydrolyzed by diverse microbial XEHs indicates that this substrate, and resorufin glycosides in general, may find broad applicability for the analysis of wall restructuring by polysaccharide hydrolases during morphogenesis and plant-microbe interactions.

Topics: Arabidopsis; Biocatalysis; Cellulase; Enzyme Assays; Fluorescent Dyes; Fluorometry; Glycoside Hydrolases; Glycosides; Glycosyltransferases; Hydrolysis; Kinetics; Nasturtium; Organ Specificity; Oxazines; Spectrometry, Fluorescence; Substrate Specificity; Time Factors; Trichoderma

A simple and reliable continuous assay procedure for measurement of cellulase activity from several species using the new substrate resorufin-beta-D-cellobioside (Res-CB) has been developed. The product of enzyme reaction, resorufin, exhibits fluorescence emission at 585 nm with excitation at 571 nm and has a pK(a) of 5.8, which allows continuous measurement of fluorescence turnover at or near physiological pH values. The assay performed using purified cellulase from the microscopic fungus Trichoderma reesei has been shown to give the kinetic parameters K(m) of 112 microM and V(max) of 0.000673 micromol/mL/min. Methods for performing the assay using cellulases isolated from both live Arabidopsis thaliana plant and Aspergillus niger fungal species are presented.

Topics: Arabidopsis; Aspergillus niger; Cellobiose; Cells, Cultured; Cellulase; Disaccharides; Fluorescent Dyes; Hydrogen-Ion Concentration; Kinetics; Oxazines; Spectrometry, Fluorescence; Time Factors