Gold Nicholas D, Martin Vincent J J
Department of Biology, Concordia University, Montréal, Québec, Canada H4B 1R6.
J Bacteriol. 2007 Oct;189(19):6787-95. doi: 10.1128/JB.00882-07. Epub 2007 Jul 20.
A metabolic isotope-labeling strategy was used in conjunction with nano-liquid chromatography-electrospray ionization mass spectrometry peptide sequencing to assess quantitative alterations in the expression patterns of subunits within cellulosomes of the cellulolytic bacterium Clostridium thermocellum, grown on either cellulose or cellobiose. In total, 41 cellulosomal proteins were detected, including 36 type I dockerin-containing proteins, which count among them all but three of the known docking components and 16 new subunits. All differential expression data were normalized to the scaffoldin CipA such that protein per cellulosome was compared for growth between the two substrates. Proteins that exhibited higher expression in cellulosomes from cellulose-grown cells than in cellobiose-grown cells were the cell surface anchor protein OlpB, exoglucanases CelS and CelK, and the glycoside hydrolase family 9 (GH9) endoglucanase CelJ. Conversely, lower expression in cellulosomes from cells grown on cellulose than on cellobiose was observed for the GH8 endoglucanase CelA; GH5 endoglucanases CelB, CelE, CelG; and hemicellulases XynA, XynC, XynZ, and XghA. GH9 cellulases were the most abundant group of enzymes per CipA when cells were grown on cellulose, while hemicellulases were the most abundant group on cellobiose. The results support the existing theory that expression of scaffoldin-related proteins is coordinately regulated by a catabolite repression type of mechanism, as well as the prior observation that xylanase expression is subject to a growth rate-independent type of regulation. However, concerning transcriptional control of cellulases, which had also been previously shown to be subject to catabolite repression, a novel distinction was observed with respect to endoglucanases.
采用代谢同位素标记策略，结合纳升液相色谱-电喷雾电离质谱肽测序技术，评估在纤维素或纤维二糖上生长的嗜热栖热放线菌纤维素体中亚基表达模式的定量变化。总共检测到41种纤维素体蛋白，包括36种含I型dockerin的蛋白，其中包括除三种已知对接成分外的所有成分以及16种新亚基。所有差异表达数据均以支架蛋白CipA进行归一化处理，以便比较两种底物生长时每个纤维素体中的蛋白质。在纤维素生长细胞的纤维素体中表达高于纤维二糖生长细胞的蛋白质有细胞表面锚定蛋白OlpB、外切葡聚糖酶CelS和CelK，以及糖苷水解酶家族9（GH9）内切葡聚糖酶CelJ。相反，在纤维素上生长的细胞的纤维素体中，GH8内切葡聚糖酶CelA、GH5内切葡聚糖酶CelB、CelE、CelG以及半纤维素酶XynA、XynC、XynZ和XghA的表达低于在纤维二糖上生长的细胞。当细胞在纤维素上生长时，GH9纤维素酶是每个CipA中最丰富的酶组，而半纤维素酶在纤维二糖上生长时是最丰富的酶组。这些结果支持了现有理论，即支架蛋白相关蛋白的表达受分解代谢物阻遏类型机制的协调调节，以及先前的观察结果，即木聚糖酶表达受生长速率无关类型的调节。然而，关于纤维素酶的转录控制，此前也已证明其受分解代谢物阻遏，在内切葡聚糖酶方面观察到了一种新的区别。
