People working on this project:
Cellulose is the most abundant biopolymer on earth and holds an important biological role in maintaining the structural rigidity of plant cell walls. Due to its abundance, cellulosic biomass holds great promise as a feedstock for second generation biofuels. As a part of the Energy Biosciences Institute (EBI) we are working as part of an interdisciplinary team to make the vision of turning plant biomass into fuels a reality.
Currently the bottleneck to production of second-generation fuels lies in the relatively expensive and slow enzymatic degradation of cellulose to glucose monomers. The extensive hydrogen-bonding network within and between chains means that cellulose is an insoluble, heterogenous substrate and hence cellulose-active enzymes are very different than enzymes that catalyze reactions on soluble substrates. To add to this complexity, most fungi contain dozens of enzymes that are active on cellulose, and the reason for such redundancy is largely a mystery. Currently the best mechanistic models of cellulose degradation rely on the activity of three types of enzymes: endocellulases that hydrolyze glycosidic bonds within chains, exocellulases (or cellobiohydrolases) that hydrolyze from the ends of chains, and beta-glucosidases that cleave cellobiose into glucose monomers. We are trying to build on this fundamental understanding of cellulose degradation and understand the roles for other types of carbohydrate-active enzymes.
As a model organism we are studying Neurospora crassa, a filamentous fungus and an efficient degrader of plant biomass. Filamentous fungi like N. crassa are responsible for the vast majority of enzymatic cellulose degradation in Nature, and they are also the most promising candidates for the development of enzymes to produce second-generation biofuels. Taking advantage of whole-genome microarrays, RNA-Seq technology, and a publicly available whole-genome gene deletion set, we identified a number of previously uncharacterized enzymes likely to be involved in cellulose degradation. This search led us to a family of copper-dependent hydroxylases (previously annotated as GH61 proteins) that are involved in catalyzing a monooxygenase reaction that breaks internal linkages within the cellulose backbone. We are continuing to purify and characterize these enzymes to gain a fundamental understanding of how individual enzymes carry out their respective catalytic functions and, more importantly, how these enzymes work together to efficiently degrade plant cell walls.
Vu VV, Hangasky JA, Detomasi TC, Henry SJW, Ngo ST. Span EA, Marletta MA. Substrate selectivity in starch polysaccharide monooxygenases JBC, 2019
Goncalves AP, Heller J, Span EA, Rosenfield G, Do HP, Palma-Guerrero J, Requena N, Marletta MA, Glass NL. Allorecognition upon fungal cell-cell contact determines social cooperation and impacts the acquisition of multicellularity Current Biology, 2019
Hangasky JA, Detomasi TC, Marletta MA. Glycosidic bond hydroxylation by polysaccharide monooxygenases. Trends in Chemistry 2019.
Hangasky JA and Marletta MA. A random-sequential kinetic mechanism for polysaccharide monooxygenases. Biochemistry 2018.
Agostoni M, Hangasky JA, Marletta MA. Physiological and molecular understanding of bacterial polysaccharide monooxygenases. MMBR 81 2017.
Span E, Suess DLM, Deller MC, Britt RD, Marletta MA. The role of the secondary coordination sphere in a fungal polysaccharide monooxygenase. ACS Chem Biol. 2017.
Vu VV and Marletta MA. Starch-degrading polysaccharide monooxygenases. Cell Mol Life Sci. 2016; 73:2809-19.
Span EA, Marletta MA. The framework of polysaccharide monooxygenase structure and chemistry. Curr Opin Struct Biol. 2015 Nov 23;35:93-99.
Beeson WT, Vu VV, Span EA, Phillips CM, Marletta MA. Cellulose degradation by polysaccharide monooxygenases. Annu Rev Biochem. 2015 84:923-46.
Vu VV, Beeson WT, Span EA, Farquhar ER, Marletta MA. A family of starch-active polysaccharide monooxygenases. Proc Natl Acad Sci USA. 2014, 111, 13822-7.
Vu VV, Beeson WT, Phillips CM, Cate JH, Marletta MA. Determinants of regioselective hydroxylation in the fungal polysaccharide monooxygenases. J Am Chem Soc 2014, 136:562-5.
Beeson WT, Phillips CM, Cate JH, Marletta MA. Oxidative cleavage of cellulose by fungal copper-dependent polysaccharide monooxygenases. J Am Chem Soc 2012, 134:890-2.
Phillips CM, Beeson WT, Cate JH, Marletta MA. Cellobiose dehydrogenase and a copper-dependent polysaccharide monooxygenase potentiate cellulose degradation by Neurospora crassa. ACS Chem Biol 2011, 6:1399-406.
Phillips CM, Iavarone AT, Marletta MA. A quantitative proteomic approach to cellulose degradation by Neurospora crassa. J Proteome Res 2011, 10:4177-85.
Beeson WT 4th, Iavarone AT, Hausmann CD, Cate JH, Marletta MA. Extracellular aldonolactonase from Myceliophthora thermophila. Appl Environ Microbiol 2010, 77:650-6.
Sun J*, Phillips CM*, Anderson CT, Beeson WT, Marletta MA, Glass NL. Expression and characterization of the Neurospora crassa endoglucanase GH5-1. Prot Expr Purif 2011, 75:147-54.
Tian C*, Beeson WT*, Iavarone AT, Sun J, Marletta MA, Cate JH, Glass NL. Systems analysis of plant cell wall degradation by the filamentous fungi Neurospora crassa. Proc Natl Acad Sci USA. 2009, 106:22157-62.