Colourimetric and fluorimetric substrates for the assay of limit dextrinase.
Mangan, D., McCleary, B. V., Cornaggia, C., Ivory, R., Rooney, E. & McKie, V. (2015). Journal of Cereal Science, 62, 50-57.
The measurement of limit-dextrinase (LD) (EC 22.214.171.124) in grain samples such as barley, wheat or rice can be problematic for a number of reasons. The intrinsic LD activity in these samples is extremely low and they often contain a limit-dextrinase inhibitor and/or high levels of reducing sugars. LD also exhibits transglycosylation activity that can complicate the measurement of its hydrolytic activity. A minor modification to the industrial standard Limit-Dextrizyme tablet test is suggested here to overcome this transglycosylation issue. In addition, two new substrates are described that can be adopted for use in an auto-analyser format. 4,6-O-benzylidene-2-chloro-4-nitrophenyl-β-63-α-D-maltotriosyl-maltotrioside (BzCNPG3G3, Hexachrom) is not susceptible to transglycosylation and serves amiably as a routine quantitative assay tool with the potential to run kinetic assays due to the low pK (~5.5) of the chromogenic moiety while 4,6-O-benzylidene-4-methylumbelliferyl-β-63-α-D-maltotriosyl-maltotrioside (BzMUG3G3, Hexafluor) was found to be susceptible to transglycosylation with LD. It is anticipated that Hexafluor may find extensive use in applications where high sensitivity is required such as high throughput screening studies.
The Multi Domain Caldicellulosiruptor bescii CelA Cellulase Excels at the Hydrolysis of Crystalline Cellulose.
Brunecky, R., Donohoe, B. S., Yarbrough, J. M., Mittal, A., Scott, B. R., Ding, H., Taylor II, L., E., Russell, J. F., Chung, D., Westpheling, J., Teter, S. A., Himmel, M. E. & Bomble, Y. J. (2017). Scientific Reports, 7, 9622.
The crystalline nature of cellulose microfibrils is one of the key factors influencing biomass recalcitrance which is a key technical and economic barrier to overcome to make cellulosic biofuels a commercial reality. To date, all known fungal enzymes tested have great difficulty degrading highly crystalline cellulosic substrates. We have demonstrated that the CelA cellulase from Caldicellulosiruptor bescii degrades highly crystalline cellulose as well as low crystallinity substrates making it the only known cellulase to function well on highly crystalline cellulose. Unlike the secretomes of cellulolytic fungi, which typically comprise multiple, single catalytic domain enzymes for biomass degradation, some bacterial systems employ an alternative strategy that utilizes multi-catalytic domain cellulases. Additionally, CelA is extremely thermostable and highly active at elevated temperatures, unlike commercial fungal cellulases. Furthermore we have determined that the factors negatively affecting digestion of lignocellulosic materials by C. bescii enzyme cocktails containing CelA appear to be significantly different from the performance barriers affecting fungal cellulases. Here, we explore the activity and degradation mechanism of CelA on a variety of pretreated substrates to better understand how the different bulk components of biomass, such as xylan and lignin, impact its performance.
High activity CAZyme cassette for improving biomass degradation in thermophiles.
Brunecky, R., Chung, D., Sarai, N. S., Hengge, N., Russell, J. F., Young, J., Mittal, A., Pason, P., Vander Wall, T., Michener, W., Shollenberger, T., Westpheling, J. Himmel, M. E. & Bomble, Y. J. (2018). Biotechnology for Biofuels, 11(1), 22.
Background: Thermophilic microorganisms and their enzymes offer several advantages for industrial application over their mesophilic counterparts. For example, a hyperthermophilic anaerobe, Caldicellulosiruptor bescii, was recently isolated from hot springs in Kamchatka, Siberia, and shown to have very high cellulolytic activity. Additionally, it is one of a few microorganisms being considered as viable candidates for consolidated bioprocessing applications. Moreover, C. bescii is capable of deconstructing plant biomass without enzymatic or chemical pretreatment. This ability is accomplished by the production and secretion of free, multi-modular and multi-functional enzymes, one of which, CbCel9A/Cel48A also known as CelA, is able to outperform enzymes found in commercial enzyme preparations. Furthermore, the complete C. bescii exoproteome is extremely thermostable and highly active at elevated temperatures, unlike commercial fungal cellulases. Therefore, understanding the functional diversity of enzymes in the C. bescii exoproteome and how inter-molecular synergy between them confers C. bescii with its high cellulolytic activity is an important endeavor to enable the production of more efficient biomass degrading enzyme formulations and in turn, better cellulolytic industrial microorganisms. Results: To advance the understanding of the C. bescii exoproteome we have expressed, purified, and tested four of the primary enzymes found in the exoproteome and we have found that the combination of three or four of the most highly expressed enzymes exhibit synergistic activity. We also demonstrated that discrete combinations of these enzymes mimic and even improve upon the activity of the whole C. bescii exoproteome, even though some of the enzymes lack significant activity on their own. Conclusions: We have demonstrated that it is possible to replicate the cellulolytic activity of the native C. bescii exoproteome utilizing a minimal gene set, and that these minimal gene sets are more active than the whole exoproteome. In the future, this may lead to more simplified and efficient cellulolytic enzyme preparations or yield improvements when these enzymes are expressed in microorganisms engineered for consolidated bioprocessing.