Journal
MICROBIOLOGY AND MOLECULAR BIOLOGY REVIEWS
Volume 78, Issue 4, Pages 588-613Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/MMBR.00019-14
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Funding
- Oklahoma Bioenergy Center, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico [310177/2011-1]
- Fundacao de Amparo a Pesquisa do Estado de Sao Paulo [2012/20549-4, 2013/18910-3, 2008/58037-9, 2010/18198-3]
- National Renewable Energy Laboratory [ZDJ-7-77608-01]
- U.S. Department of Agriculture (CSREES) [2007-35504-18244]
- U.S. Department of Energy and Edenspace Corp. [06103-OKL]
- Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [10/18198-3, 08/58037-9] Funding Source: FAPESP
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Biomass is constructed of dense recalcitrant polymeric materials: proteins, lignin, and holocellulose, a fraction constituting fibrous cellulose wrapped in hemicellulose-pectin. Bacteria and fungi are abundant in soil and forest floors, actively recycling biomass mainly by extracting sugars from holocellulose degradation. Here we review the genome-wide contents of seven Aspergillus species and unravel hundreds of gene models encoding holocellulose-degrading enzymes. Numerous apparent gene duplications followed functional evolution, grouping similar genes into smaller coherent functional families according to specialized structural features, domain organization, biochemical activity, and genus genome distribution. Aspergilli contain about 37 cellulase gene models, clustered in two mechanistic categories: 27 hydrolyze and 10 oxidize glycosidic bonds. Within the oxidative enzymes, we found two cellobiose dehydrogenases that produce oxygen radicals utilized by eight lytic polysaccharide monooxygenases that oxidize glycosidic linkages, breaking crystalline cellulose chains and making them accessible to hydrolytic enzymes. Among the hydrolases, six cellobiohydrolases with a tunnel-like structural fold embrace single crystalline cellulose chains and cooperate at nonreducing or reducing end termini, splitting off cellobiose. Five endoglucanases group into four structural families and interact randomly and internally with cellulose through an open cleft catalytic domain, and finally, seven extracellular beta-glucosidases cleave cellobiose and related oligomers into glucose. Aspergilli contain, on average, 30 hemicellulase and 7 accessory gene models, distributed among 9 distinct functional categories: the backbone-attacking enzymes xylanase, mannosidase, arabinase, and xyloglucanase, the short-side-chain-removing enzymes xylan alpha-1,2-glucuronidase, arabinofuranosidase, and xylosidase, and the accessory enzymes acetyl xylan and feruloyl esterases.
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