Date: Oct 21, 2012 Source: Nature Biotechnology (
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Binzhang Shen,
Xueguang Sun,
Xiao Zuo,
Taran Shilling,
James Apgar,
Mary Ross,
Oleg Bougri,
Vladimir Samoylov,
Matthew Parker,
Elaina Hancock,
Hector Lucero,
Benjamin Gray,
Nathan A Ekborg,
Dongcheng Zhang,
Jeremy C Schley Johnson,
Gabor Lazar
& R Michael Raab
Abstract
Plant cellulosic biomass is an abundant, low-cost feedstock for producing biofuels and chemicals. Expressing cell wall--degrading (CWD) enzymes (e.g. xylanases) in plant feedstocks could reduce the amount of enzymes required for feedstock pretreatment and hydrolysis during bioprocessing to release soluble sugars. However, in planta expression of xylanases can reduce biomass yield and plant fertility. To overcome this problem, we engineered a thermostable xylanase (XynB) with a thermostable self-splicing bacterial intein to control the xylanase activity. Intein-modified XynB (iXynB) variants were selected that have <10% wild-type enzymatic activity but recover >60% enzymatic activity upon intein self-splicing at temperatures >59 °C. Greenhouse-grown xynB maize expressing XynB has shriveled seeds and low fertility, but ixynB maize had normal seeds and fertility. Processing dried ixynB maize stover by temperature-regulated xylanase activation and hydrolysis in a cocktail of commercial CWD enzymes produced >90% theoretical glucose and >63% theoretical xylose yields.
