Cellulose-hydrolyzing bacteria enzyme systems

Humans have an enzyme called a-amylase in saliva and pancreatic juices that hydrolyze the a-l,4-glycosidic bonds of starches, but not the j8-l,4-glycosidic bonds of cellulose. Thus, humans cannot digest cellulose. Animals snch as horses, cows, and goats can obtain glucose from cellulose because their digestive systems contain bacteria that provide enzymes such as cellulase to hydrolyze j8-l,4-glycosidic bonds. 

For many years, plant cellulases were thought, contrarily to bacteria and fungi cellulases, not to have CBMs. Nevertheless, putative CBM sequences were found in a tomato cellulose, in 1998 [105]. Since then, putative CBMs were described in peach [106], pear [107], strawberry [108] and mango [109]. However, only recently the first CBM from plant was described (present in a tomato cellulase), and a new CBM family was born (CBM49) [110]. The tomato cellulase is highly sensitive to proteolysis in the linker region, when expressed in a heterologous system. Therefore, the respective sequence was fused with a catalytic domain of another well studied cellulase, from T. fusca. It was shown that the fusion enzyme was able to bind and hydrolyze crystalline cellulose. 

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