Eijsink Vincent G H, Vaaje-Kolstad Gustav, Vårum Kjell M, Horn Svein J
Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, As, Norway.
Trends Biotechnol. 2008 May;26(5):228-35. doi: 10.1016/j.tibtech.2008.02.004. Epub 2008 Mar 25.
Enzymatic conversion of structural polysaccharides in plant biomass is a key issue in the development of second generation ('lignocellulosic') bioethanol. The efficiency of this process depends in part on the ability of enzymes to disrupt crystalline polysaccharides, thus gaining access to single polymer chains. Recently, new insights into how enzymes accomplish this have been obtained from studies on enzymatic conversion of chitin. First, chitinolytic microorganisms were shown to produce non-hydrolytic accessory proteins that increase enzyme efficiency. Second, it was shown that a processive mechanism, which is generally considered favorable because it improves substrate accessibility, might in fact slow down enzymes. These findings suggest new focal points for the development of enzyme technology for depolymerizing recalcitrant polysaccharide biomass. Improving substrate accessibility should be a key issue because this might reduce the need for using processive enzymes, which are intrinsically slow and abundantly present in current commercial enzyme preparations for biomass conversion. Furthermore, carefully selected substrate-disrupting accessory proteins or domains might provide novel tools to improve substrate accessibility and thus contribute to more efficient enzymatic processes.
植物生物质中结构多糖的酶促转化是第二代（“木质纤维素”）生物乙醇开发中的关键问题。该过程的效率部分取决于酶破坏结晶多糖的能力，从而得以接触单个聚合物链。最近，通过对几丁质酶促转化的研究，人们对酶如何完成这一过程有了新的认识。首先，已表明几丁质分解微生物会产生提高酶效率的非水解辅助蛋白。其次，已表明一种通常被认为有利的连续作用机制，因为它能改善底物可及性，但实际上可能会使酶变慢。这些发现为开发用于解聚顽固多糖生物质的酶技术指明了新的重点。提高底物可及性应是一个关键问题，因为这可能减少使用连续作用酶的需求，这类酶本质上速度较慢且在当前用于生物质转化的商业酶制剂中大量存在。此外，精心挑选的破坏底物的辅助蛋白或结构域可能提供新工具来提高底物可及性，从而有助于实现更高效的酶促过程。
