Characterization of modular bifunctional processive endoglucanase Cel5 from Hahella chejuensis KCTC 2396 |
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Authors: | Sunil Subhash Ghatge Amar Anandrao Telke Seo-Hee Kang Venkatesh Arulalapperumal Keun-Woo Lee Sanjay Prabhu Govindwar Youngsoon Um Doo-Byoung Oh Hyun-Dong Shin Seon-Won Kim |
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Institution: | 1. Division of Applied Life Sciences (BK21), PMBBRC, Gyeongsang National University, Jinju, Gyeongnam, Republic of Korea 2. Department of Biochemistry, Shivaji University, Kolhapur, Maharashtra, India 3. Center for Environmental Technology Research, Korea Institute of Science and Technology (KIST), Seoul, Republic of Korea 4. Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon, Republic of Korea 5. School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA
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Abstract: | Cel5 from marine Hahella chejuensis is composed of glycoside hydrolase family-5 (GH5) catalytic domain (CD) and two carbohydrate binding modules (CBM6-2). The enzyme was expressed in Escherichia coli and purified to homogeneity. The optimum endoglucanase and xylanase activities of recombinant Cel5 were observed at 65 °C, pH 6.5 and 55 °C, pH 5.5, respectively. It exhibited K m of 1.8 and 7.1 mg/ml for carboxymethyl cellulose and birchwood xylan, respectively. The addition of Ca2+ greatly improved thermostability and endoglucanase activity of Cel5. The Cel5 retained 90 % of its endoglucanase activity after 24 h incubation in presence of 5 M concentration of NaCl. Recombinant Cel5 showed production of cellobiose after hydrolysis of cellulosic substrates (soluble/insoluble) and methylglucuronic acid substituted xylooligosaccharides after hydrolysis of glucuronoxylans by endo-wise cleavage. These results indicated that Cel5 as bifunctional enzyme having both processive endoglucanase and xylanase activities. The multidomain structure of Cel5 is clearly distinguished from the GH5 bifunctional glycoside hydrolases characterized to date, which are single domain enzymes. Sequence analysis and homology modeling suggested presence of two conserved binding sites with different substrate specificities in CBM6-2 and a single catalytic site in CD. Residues Glu132 and Glu219 were identified as key catalytic amino acids by sequence alignment and further verified by using site directed mutagenesis. CBM6-2 plays vital role in catalytic activity and thermostability of Cel5. The bifunctional activities and multiple substrate specificities of Cel5 can be utilized for efficient hydrolysis of cellulose and hemicellulose into soluble sugars. |
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