Thursday, May 5, 2011: 3:30 PM
Grand Ballroom A, 2nd fl (Sheraton Seattle)
Traditionally, enzyme systems capable of degrading recalcitrant polysaccharides such as chitin and cellulose are considered to consist of endo-acting enzymes that cut randomly in the polysaccharide chain and processive exo-acting enzymes (chito- or cellobiohydrolases), which degrade the polymers from chain ends. Although this model is generally accepted, it remains difficult to understand how these glycoside hydrolases could act on a polysaccharide chain in its crystalline environment. We have previously shown that chitin-degrading organisms produce an additional factor, hitherto known as chitin-binding protein (Cbp), that acts synergistically with chitinases [1,2]. We show here that Cbp21 from Serratia marcsescens is an enzyme that exploits molecular oxygen and water to introduce chain breaks on the surface of crystalline chitin, thus potentiating the action of chitinases [3]. The enzyme activity is dependent on divalent cations, and its activity is boosted dramatically by the presence of reductants. These dependencies and the fact that the enzyme produces oxidized chain ends demonstrate the existence of a hitherto unknown enzyme activity. Interestingly proteins classified as family GH61 glycoside hydrolases are likely to have a similar activity on cellulose. Our findings provide new avenues towards more efficient enzymatic conversion of biomass.
[1] Vaaje-Kolstad G, Horn SJ, van Aalten DM, Synstad B, Eijsink VGH (2005) J. Biol. Chem. 280:28492-28497.
[2] Eijsink VGH, Vaaje-Kolstad G, Varum KM, Horn SJ (2008). Trends Biotech. 26:228-235.
[3] Vaaje-Kolstad G, Westereng B, Horn SJ, Liu Z, Zhai H, Sørlie M, Eijsink VGH (2010) Science 330:219-222.