Novel, acidic, and cold-adapted glycoside hydrolase family 8 endo-β-1,4-glucanase from an Antarctic lichen-associated bacterium, Lichenicola cladoniae PAMC 26568

• Published in: Frontiers in Microbiology
• Main Authors: Kim, Do Young, Kim, Jonghoon, Lee, Yung Mi, Byeon, Soo Min, Gwak, Jeong Hae, Lee, Jong Suk, Shin, Dong-Ha, Park, Ho-Yong
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Frontiers Media SA 2022
• Subjects: Antarc*; Antarctic
• Online Access: http://dx.doi.org/10.3389/fmicb.2022.935497; https://www.frontiersin.org/articles/10.3389/fmicb.2022.935497/full

Endo-β-1,4-glucanase is a crucial glycoside hydrolase (GH) involved in the decomposition of cellulosic materials. In this study, to discover a novel cold-adapted β-1,4- D -glucan-degrading enzyme, the gene coding for an extracellular endo-β-1,4-glucanase (GluL) from Lichenicola cladoniae PAMC 26568, an Antarctic lichen ( Cladonia borealis )-associated bacterium, was identified and recombinantly expressed in Escherichia coli BL21. The GluL gene (1044-bp) encoded a non-modular polypeptide consisting of a single catalytic GH8 domain, which shared the highest sequence identity of 55% with that of an uncharacterized protein from Gluconacetobacter takamatsuzukensis (WP_182950054). The recombinant endo-β-1,4-glucanase (rGluL: 38.0 kDa) most efficiently degraded sodium carboxymethylcellulose (CMC) at pH 4.0 and 45°C, and showed approximately 23% of its maximum degradation activity even at 3°C. The biocatalytic activity of rGluL was noticeably enhanced by >1.3-fold in the presence of 1 mM Mn 2+ or NaCl at concentrations between 0.1 and 0.5 M, whereas the enzyme was considerably downregulated by 1 mM Hg 2+ and Fe 2+ together with 5 mM N -bromosuccinimide and 0.5% sodium dodecyl sulfate. rGluL is a true endo-β-1,4-glucanase, which could preferentially decompose D -cellooligosaccharides consisting of 3 to 6 D -glucose, CMC, and barley β-glucan, without other additional glycoside hydrolase activities. The specific activity (15.1 U mg –1 ) and k cat / K m value (6.35 mg –1 s –1 mL) of rGluL toward barley β-glucan were approximately 1.8- and 2.2-fold higher, respectively, compared to its specific activity (8.3 U mg –1 ) and k cat / K m value (2.83 mg –1 s –1 mL) toward CMC. The enzymatic hydrolysis of CMC, D -cellotetraose, and D -cellohexaose yielded primarily D -cellobiose, accompanied by D -glucose, D -cellotriose, and D -cellotetraose. However, the cleavage of D -cellopentaose by rGluL resulted in the production of only D -cellobiose and D -cellotriose. The findings of the present study imply that rGluL is a novel, ...