Soni Surabhi, Sathe Sneha S, Odaneth Annamma A, Lali Arvind M, Chandrayan Sanjeev K
DBT-ICT Centre for Energy Biosciences, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga (East), Mumbai, Maharashtra, 400019, India.
Department of Chemical Engineering, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga (East), Mumbai, Maharashtra, 400019, India.
Extremophiles. 2017 Jul;21(4):687-697. doi: 10.1007/s00792-017-0934-2. Epub 2017 Apr 25.
Caldicellulosiruptor bescii, the most thermophilic cellulolytic bacterium, is rich in hydrolytic and accessory enzymes that can degrade untreated biomass, but the precise role of many these enzymes is unknown. One of such enzymes is a predicted GDSL lipase or esterase encoded by the locus Athe_0553. In this study, this probable esterase named as Cbes-AcXE2 was overexpressed in Escherichia coli. The Ni-NTA affinity purified enzyme exhibited an optimum pH of 7.5 at an optimum temperature of 70 °C. Cbes-AcXE2 hydrolyzed p-nitrophenyl (pNP) acetate, pNP-butyrate, and phenyl acetate with approximately equal efficiency. The specific activity and K for the most preferred substrate, phenyl acetate, were 142 U/mg and 0.85 mM, respectively. Cbes-AcXE2 removed the acetyl group of xylobiose hexaacetate and glucose pentaacetate like an acetyl xylan esterase (AcXE). Bioinformatics analyses suggested that Cbes-AcXE2, which carries an SGNH hydrolase-type esterase domain, is a member of an unclassified carbohydrate esterase (CE) family. Moreover, Cbes-AcXE2 is evolutionarily and biochemically similar to an unclassified AcXE, Axe2, of Geobacillus stearothermophilus. Thus, we proposed a novel family of carbohydrate esterase for both Cbes-AcXE2 and Axe2.
嗜热栖热放线杆菌（Caldicellulosiruptor bescii）是最嗜热的纤维素分解细菌，富含能够降解未处理生物质的水解酶和辅助酶，但许多这些酶的确切作用尚不清楚。其中一种酶是由Athe_0553位点编码的预测GDSL脂肪酶或酯酶。在本研究中，这种可能的酯酶命名为Cbes-AcXE2，在大肠杆菌中过表达。镍-亚氨基二乙酸（Ni-NTA）亲和纯化的酶在70℃的最适温度下表现出7.5的最适pH值。Cbes-AcXE2以大致相同的效率水解对硝基苯基（pNP）乙酸酯、pNP-丁酸酯和苯乙酸酯。最优选底物苯乙酸酯的比活性和K分别为142 U/mg和0.85 mM。Cbes-AcXE2像乙酰木聚糖酯酶（AcXE）一样去除木二糖六乙酸酯和葡萄糖五乙酸酯的乙酰基。生物信息学分析表明，携带SGNH水解酶型酯酶结构域的Cbes-AcXE2是未分类碳水化合物酯酶（CE）家族的成员。此外，Cbes-AcXE2在进化和生化方面与嗜热栖热芽孢杆菌（Geobacillus stearothermophilus）未分类的AcXE Axe2相似。因此，我们为Cbes-AcXE2和Axe2提出了一个新的碳水化合物酯酶家族。
