Enzymatic transformation of nonfood biomass to starch

Abstract

The global demand for food could double in another 40 y owing to growth in the population and food consumption per capita. To meet the world's future food and sustainability needs for biofuels and renewable materials, the production of starch-rich cereals and cellulose-rich bioenergy plants must grow substantially while minimizing agriculture's environmental footprint and conserving biodiversity. Here we demonstrate one-pot enzymatic conversion of pretreated biomass to starch through a nonnatural synthetic enzymatic pathway composed of endoglucanase, cellobiohydrolyase, cellobiose phosphorylase, and alpha-glucan phosphorylase originating from bacterial, fungal, and plant sources. A special polypeptide cap in potato alpha-glucan phosphorylase was essential to push a partially hydrolyzed intermediate of cellulose forward to the synthesis of amylose. Up to 30% of the anhydroglucose units in cellulose were converted to starch; the remaining cellulose was hydrolyzed to glucose suitable for ethanol production by yeast in the same bioreactor. Next-generation biorefineries based on simultaneous enzymatic biotransformation and microbial fermentation could address the food, biofuels, and environment trilemma.bioeconomy | food and feed | synthetic amylose | in vitro synthetic biology | cell-free biomanufacturing T he continuing growth of the population and food consumption per capita means that the global demand for food could increase by 50-100% by 2050 (1, 2), and ∼30% of the world's agricultural land and 70% of the world's fresh water withdrawals are being used for the production of food and feed to support 7 billion people (3, 4). Starch is the most important dietary component because it accounts for more than half of the consumed carbohydrates, which provide 50-60% of the calories needed by humans. Starch is composed of polysaccharides consisting of a large number of glucose units joined together primarily by alpha-1,4-glycosidic bonds and alpha-1,6-glycosidic bonds. Linear-chain amylose is more valuable than branched amylopectin because it can be used as a precursor for making high-quality transparent, flexible, low-oxygen-diffusion plastic sheets and films (5, 6); tailored functional food or additives for lowering the risk of serious noninfectious diseases (e.g., diabetes and obesity) (7, 8); and a potential high-density hydrogen carrier (9-11). Also, it is easy to convert linear amylose to branched amylopectin by using alphaglucan-branching glycosyltransferase (12).Cellulose, a linear glucan linked by beta-1,4-glycosidic bonds, is the supporting material of plant cell walls and the most abundant carbohydrate on Earth. The annual resource of cellulosic materials is ∼40 times greater than the starch produced by crops cultivated for food and feed. In addition, (perennial) cellulosic plants and dedicated bioenergy crops can grow on low-quality land, even on marginal land, and require fewer inputs such as fertilizers, herbicides, pesticides, and water, whereas annual high-productivity starch-rich crops require high-qual...

A high-energy-density sugar biobattery based on a synthetic enzymatic pathway

“…Maltodextrin, a partially hydrolysed starch fragment, is a superior fuel to glucose in EFCs, because maltodextrin has 11% higher energy density than glucose. Maltodextrin is also less costly because glucose is the main product of its enzymatic hydrolysis, and low-cost linear maltodextrin can be made from cellulose 17 . An equivalent weight of maltodextrin has a much lower osmotic pressure than glucose.…”

“…Starch is the most widely used energy-storage compound in nature. The catabolism of starch allows for a slow and nearly constant release of chemical energy in living cells that is different from its monomer glucose 17 . Maltodextrin, a partially hydrolysed starch fragment, is a superior fuel to glucose in EFCs, because maltodextrin has 11% higher energy density than glucose.…”

Integrated enzymatic catalysis for biomass deconstruction: a partnership for a sustainable future

“…Recently, You et al developed a simple enzyme purification and co-immobilization process using Avicel-containing nanomagnetic particles (A-NMPs) [17]. Cellulose was transformed into amylose in a one-pot reaction through the formation of cellobiose intermediate using this immobilized catalytic system [ Figure 3].…”

In vitro conversion of glycerol to lactate with thermophilic enzymes

“…A possible solution to this problem is to avoid the use of living microorganisms and to construct an in vitro artificial metabolic pathway in which only a limited number of enzymes are involved. Until now, a variety of in vitro synthetic pathways have been designed and constructed for the production of alcohols [3,4], organic acids [5,6], carbohydrates [7], hydrogen [8,9], bioplastic [10], and even electricity [11]. Particularly, employment of enzymes derived from thermophiles and hyperthermophiles enables the simple preparation of catalytic modules with excellent selectivity and thermal stability [5,12].…”