Institute for Microbiology, University of Göttingen, D-3400 Göttingen, Federal Republic of Germany; Department of Biochemistry, University College, Galway, Ireland ; National Food Research Institute, Yatabe, Tsukuba-gun, Ibaraki 305, Japan ; and Center for Biological Resource Recovery and Department of Biochemistry, University of Georgia, Athens, Georgia 30602.
Appl Environ Microbiol. 1987 Dec;53(12):2785-92. doi: 10.1128/aem.53.12.2785-2792.1987.
Clostridium thermocellum JW20 and YM4 both synthesize cellulolytic enzyme complexes, cellulosomes, when grown on medium containing cellulose. Electron microscopic studies showed that, in the early stages of growth of strain JW20, clusters of tightly packed cellulosomes, i.e., polycellulosomes, were located on the cell surface and were bound to cellulose. The polycellulosome was estimated to have a particle mass of 50 x 10 to 80 x 10 daltons (Da), while that of the cellulosome was estimated to be 2 x 10 to 2.5 x 10 Da and to contain about 35 polypeptides ranging from 20 to 200 kDa. The cellulosome produced by strain YM4 was found to be somewhat larger, with the estimated particle mass being 3.5 x 10 Da, and the number of polypeptides was counted to be 45 to 50, ranging from 20 to 200 kDa. In the early stages of cultivation, the cellulosomes from both species exist as tightly packed complexes (tight cellulosomes). These subsequently decompose to loosely packed complexes (loose cellulosomes) and ultimately to free polypeptides. Examination of the loose cellulosomal particles showed that they contain rows of equidistantly spaced, similarly sized polypeptide subunits, with an apparently identical orientation arranged parallel to the major axis of the cellulosome. It is postulated that on binding of a cellulose chain alongside such a row of subunits a simultaneous multicutting event occurs that leads to the release of cellooligosaccharides of four cellobiose units in length (C(4)). Rows of smaller-sized subunits with lower center-to-center distances, which are also present in the cellulosome, subsequently cleave the C(4) fragments (or cellulose) to C(2) (cellotetraose) or C(1) (cellobiose). In this way the cellulosome can catalyze the complete hydrolysis of cellulose.
嗜热纤维梭菌 JW20 和 YM4 均在含有纤维素的培养基中生长时合成纤维酶复合体系，即纤维小体。电子显微镜研究表明，在 JW20 菌株的早期生长阶段，紧密堆积的纤维小体簇，即多纤维小体，位于细胞表面并与纤维素结合。多纤维小体的颗粒质量估计为 50×10 至 80×10 道尔顿（Da），而纤维小体的颗粒质量估计为 2×10 至 2.5×10 Da，并且包含约 35 种大小在 20 至 200 kDa 之间的多肽。发现 YM4 菌株产生的纤维小体稍大，估计颗粒质量为 3.5×10 Da，多肽数量计数为 45 至 50 种，大小在 20 至 200 kDa 之间。在培养的早期阶段，两种物种的纤维小体均以紧密堆积的复合物（紧密纤维小体）存在。这些随后分解为松散堆积的复合物（松散纤维小体），最终为游离多肽。对松散纤维小体颗粒的检查表明，它们包含排列成行的、等距间隔的、大小相似的多肽亚基，具有与纤维小体的主要轴平行排列的明显相同的取向。据推测，在纤维素链与这样的亚基行结合时，同时发生多切割事件，导致释放长度为四个纤维二糖单元的纤维寡糖（C(4)）。较小尺寸的亚基行也存在于纤维小体中，它们具有较低的中心到中心距离，随后切割 C(4)片段（或纤维素）至 C(2)（纤维四糖）或 C(1)（纤维二糖）。通过这种方式，纤维小体可以催化纤维素的完全水解。
