Instituto Cajal, Department of Molecular, Cellular and Developmental Neurobiology. IC-CSIC, Avenida Doctor Arce 37, 28002 Madrid, Spain.
Biomater Sci. 2020 Jul 7;8(13):3601-3610. doi: 10.1039/c9bm02052g. Epub 2020 Mar 31.
Lignocellulose is the most abundant renewable carbon source in the biosphere. However, the main bottleneck in its conversion to produce second generation biofuels is the saccharification step: the hydrolysis of lignocellulosic material into soluble fermentable sugars. Some anaerobic bacteria have developed an extracellular multi-enzyme complex called the cellulosome that efficiently degrades cellulosic substrates. Cellulosome complexes rely on enzyme-integrating scaffoldins that are large non-catalytic scaffolding proteins comprising several cohesin modules and additional functional modules that mediate the anchoring of the complex to the cell surface and the specific binding to its cellulosic substrate. It was proposed that mechanical forces may affect the cohesins positioned between the cell- and cellulose-anchoring points in the so-called connecting region. Consequently, the mechanical resistance of cohesins within the scaffoldin is of great importance, both to understand cellulosome function and as a parameter of industrial interest, to better mimic natural complexes through the use of the established designer cellulosome technology. Here we study how the mechanical stability of cohesins in a scaffoldin affects the enzymatic activity of a cellulosome. We found that when a cohesin of low mechanical stability is positioned in the connecting region of a scaffoldin, the activity of the resulting cellulosome is reduced as opposed to a cohesin of higher mechanical stability. This observation directly relates mechanical stability of the scaffoldin-borne cohesins to cellulosome activity and provides a rationale for the design of artificial cellulosomes for industrial applications, by incorporating mechanical stability as a new industrial parameter in the biotechnology toolbox.
木质纤维素是生物圈中最丰富的可再生碳源。然而，将其转化为生产第二代生物燃料的主要瓶颈是糖化步骤：将木质纤维素材料水解为可溶的发酵性糖。一些厌氧菌已经开发出一种称为纤维小体的细胞外多酶复合物，它能够有效地降解纤维素底物。纤维小体复合物依赖于酶整合支架蛋白，这些支架蛋白是由几个黏合模块和额外的功能模块组成的非催化支架蛋白，介导复合物与细胞表面的锚定和与纤维素底物的特异性结合。有人提出，机械力可能会影响所谓的连接区域中位于细胞和纤维素锚定点之间的黏合蛋白。因此，支架蛋白中黏合蛋白的机械阻力非常重要，不仅有助于理解纤维小体的功能，而且作为工业上感兴趣的参数，通过使用已建立的设计纤维小体技术更好地模拟天然复合物。在这里，我们研究了支架蛋白中黏合蛋白的机械稳定性如何影响纤维小体的酶活性。我们发现，当一个机械稳定性较低的黏合蛋白位于支架蛋白的连接区域时，与机械稳定性较高的黏合蛋白相比，产生的纤维小体的活性会降低。这一观察结果直接将支架蛋白携带的黏合蛋白的机械稳定性与纤维小体的活性联系起来，并为工业应用的人工纤维小体设计提供了依据，即将机械稳定性作为生物技术工具包中的一个新的工业参数纳入其中。
