Reference Module in Life Sciences Modular and ...

Reference Module in Life Sciences

Modular and Multifunctional Enzyme Systems for Plant Cell Wall Degradation: Diversity, Synergy, Chimeras and Magnetic-Glycosidases G. Guerriero Luxembourg Institute of Science and Technology, Esch/Alzette, Luxembourg

K.S. Siddiqui King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia

Abstract Multifunctional enzymes refer to proteins that consist of two or more catalytic modules. Many microorganisms use multifunctional enzymes to efficiently break down the recalcitrant polymeric networks that constitute plant cell walls. Currently, commercial enzyme mixtures are used in simultaneous saccharification and fermentation (SFF) process for biofuel production; these combinations are derived primarily from free enzyme systems produced by fungi. Future applications of multifunctional enzymes may represent a potential solution to the problem of high enzyme cost for processing lignocellulosic biomass into fermentable sugars. In this context, we have analyzed the modular structures of 16,937 representative genes corresponding to 34 glycoside hydrolase families putatively related to the degradation of lignocellulose in the Carbohydrate Active enZyme (CAZy) database. Among these genes, 68 gene sequences have been identified to putatively encode multifunctional enzymes, and up to five catalytic modules have been found in a single polypeptide. Based on their deduced polypeptide sequences, they can be classified into four types, that is, cellulase–cellulase, cellulase–hemicellulase, hemicellulase–hemicellulase, and hemicellulase–carbohydrate esterase. The compositional modules and architectural structures of these enzymes are analyzed here, and their putative activities on breaking down cell walls are discussed. We further discuss the predicted intramolecular synergistic mechanisms between the catalytic modules, including substrate channeling, which is a mechanism often proposed for carbohydrate-binding modules residing in multifunctional enzymes. Furthermore, the potential applications of native, engineered (chimeric and cell-surface displayed) and immobilized magnetic enzymes for biomass conversion technology are also reviewed. Citation: Guerriero G, Siddiqui, KS. 2017. Modular and multifunctional enzyme systems for plant cell wall degradation: diversity, synergy, chimeras and magnetic-glycosidases, In: Reference Module in Life Sciences, Elsevier, ISBN 9780128096338, http://dx.doi.org/10.1016/B978-0-12-809633-8.09128-7.

Vitae

Gea Guerriero is an Italian biologist who lives and works in Luxembourg. She carried out her University and PhD studies in Italy (University Federico II, Naples), where she specialized in plant physiology and molecular biology. Further, motivated by the desire to pursue a career in the Life Sciences, she decided to go abroad to widen her scientific horizons. This decision led to several years in Northern Europe working as a post-doctoral fellow in Sweden, followed by a few more years in South Tyrol and Vienna with fellowships financing independent projects. In December 2012, she joined the LIST-Luxembourg Institute of Science and Technology (ex CRPGabriel Lippmann) with a permanent position as a scientist. Her scientific activities are currently centered around the study of the plant cell wall, the natural “armor” of plant cells, and more particularly on the engineering of plant fiber properties. The research she carries out aims on one hand at unveiling specific fundamental aspects linked to fiber cell wall biosynthesis and on the other at using this knowledge to tailor the properties of plant fibers.

Khawar Sohail Siddiqui after completing his PhD in enzyme biotechnology from The Imperial College for Science, Technology and Medicine, London under the supervision of Prof. Brian S Hartley, FRS, joined National Institute for Biotechnology and Genetic Engineering (NIBGE), Faisalabad, Pakistan (1990–1999) where he established research on the chemical modification of lignocellulosic degrading enzymes for improving catalytic properties. During his stay at NIBGE, he was also involved in designing and teaching courses to MPhil (Biotechnology) related to enzymology and biotechniques. In 2001, he joined The University of New South Wales, Sydney where he worked with Prof. Rick Cavicchioli on the protein structure–function–stability relationship in cold-adapted extremophilic proteins/enzymes from Antarctic organisms. This research involved state-of-the-art bioinformatics and biophysical techniques (calorimetry, electrophoresis, chromatography, circular dichroism, UV– vis and fluorescence spectrometry, mass-spectrometry, and hydrodynamic methods). Presently, he is at the Life Sciences Department, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. His current research interests include polyextremophilic and nanomagnetic enzymes and understanding protein stability and prolonging enzyme activity whereas his teaching comprises topics related to protein structure–function, biology for engineers, techniques in life sciences and enzyme kinetics and biotechnology. He has published extensively in top peer-reviewed journals including Annual Reviews and Nature publications, contributed many chapters for books and coedited a book on extremophilic proteins in addition to serving as a reviewer. Copyright © 2017 Elsevier Inc. All rights reserved.