Department of Chemistry, Iowa State University, Ames, Iowa 50011-3111, United States.
J Am Chem Soc. 2022 Sep 21;144(37):17110-17119. doi: 10.1021/jacs.2c06848. Epub 2022 Sep 7.
Enzyme-like catalysts by design have been a long sought-after goal of chemists but difficult to realize due to the challenges in the construction of multifunctionalized active sites with accurately positioned catalytic groups for complex substrates. Hydrolysis of cellulose is a key step in biomass utilization and requires multiple enzymes to work in concert to overcome the difficulty associated with hydrolyzing the recalcitrant substrate. We here report methods to construct synthetic versions of these enzymes through covalent molecular imprinting and strategic postmodification of the imprinted sites. The synthetic catalysts cleave a cellulose chain endolytically at multiple positions or exolytically from the nonreducing end by one or three glucose units at a time, all using the dicarboxylic acid motif found in natural cellulases. By mimicking the endocellulase, exocellulase, and β-glucosidase, the synthetic catalysts hydrolyze cellulose in a synergistic manner, with an activity at 90 °C in pH 6.5 buffer more than doubled that of cellulase at pH 5 and 37 °C and 44% of that of a commercial cellulase blend (from Novozyme). As robust cross-linked polymeric nanoparticles, the synthetic catalysts showed little changes in activity after preheating at 90 °C for 3 days and could be reused, maintaining 76% of activity after 10 reaction cycles.
通过设计合成具有多功能活性位点的方法，化学家们一直致力于寻找酶类催化剂，但由于在构建具有精确定位催化基团的复杂底物多功能活性位点方面存在挑战，因此这一目标一直难以实现。纤维素的水解是生物质利用的关键步骤，需要多种酶协同作用，以克服水解顽固底物的困难。我们在这里报告了通过共价分子印迹和印迹部位的战略后修饰来构建这些酶的合成版本的方法。这些合成催化剂可以通过二羧酸基序在多个位置进行内切性切割纤维素链，或者通过一个或三个葡萄糖单元从非还原端进行外切性切割，所有这些都使用了天然纤维素酶中的二羧酸基序。通过模拟内切纤维素酶、外切纤维素酶和β-葡萄糖苷酶，合成催化剂以协同方式水解纤维素，在 90°C、pH6.5 缓冲液中的活性比 pH5 和 37°C 时的纤维素酶高两倍以上，比商业纤维素酶混合物（来自诺维信）高 44%。作为坚固的交联聚合物纳米颗粒，合成催化剂在 90°C 下预热 3 天后活性变化不大，可重复使用，在 10 次反应循环后保持 76%的活性。
