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Abstract
β-N-acetylhexosaminidases (EC 3.2.1.52) are retaining hydrolases of glycoside hydrolase family 20 (GH20). These enzymes catalyze hydrolysis of terminal, non-reducing N-acetylhexosamine residues, notably N-acetylglucosamine or N-acetylgalactosamine, in N-acetyl-β-D-hexosaminides. In nature, bacterial β-N-acetylhexosaminidases are mainly involved in cell wall peptidoglycan synthesis, analogously, fungal β-N-acetylhexosaminidases act on cell wall chitin. The enzymes work via a distinct substrate-assisted mechanism that utilizes the 2-acetamido group as nucleophile. Curiously, the β-N-acetylhexosaminidases possess an inherent trans-glycosylation ability which is potentially useful for biocatalytic synthesis of functional carbohydrates, including biomimetic synthesis of human milk oligosaccharides and other glycan-functionalized compounds. In this review, we summarize the reaction engineering approaches (donor substrate activation, additives, and reaction conditions) that have proven useful for enhancing trans-glycosylation activity of GH20 β-N-acetylhexosaminidases. We provide comprehensive overviews of reported synthesis reactions with GH20 enzymes, including tables that list the specific enzyme used, donor and acceptor substrates, reaction conditions, and details of the products and yields obtained. We also describe the active site traits and mutations that appear to favor trans-glycosylation activity of GH20 β-N-acetylhexosaminidases. Finally, we discuss novel protein engineering strategies and suggest potential “hotspots” for mutations to promote trans-glycosylation activity in GH20 for efficient synthesis of specific functional carbohydrates and other glyco-engineered products.
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Chen X, Jin L, Jiang X, Guo L, Gu G, Xu L, Lu L, Wang F, Xiao M. Converting a β-N-acetylhexosaminidase into two trans-β-N-acetylhexosaminidases by domain-targeted mutagenesis. Appl Microbiol Biotechnol 2019; 104:661-673. [PMID: 31822984 DOI: 10.1007/s00253-019-10253-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2019] [Revised: 10/29/2019] [Accepted: 11/12/2019] [Indexed: 01/14/2023]
Abstract
We have recently derived a β-N-acetylhexosaminidase, BbhI, from Bifidobacterium bifidum JCM 1254, which could regioselectively synthesize GlcNAcβ1-3Galβ1-4Glc with a yield of 44.9%. Here, directed evolution of BbhI by domain-targeted mutagenesis was carried out. Firstly, the GH20 domain was selected for random mutagenesis using MEGAWHOP method and a small library of 1300 clones was created. A total of 734 colonies with reduced hydrolytic activity were isolated, and three mutants with elevated transglycosylation yields, GlcNAcβ1-3Galβ1-4Glc yields of 68.5%, 74.7%, and 81.1%, respectively, were obtained. Subsequently, nineteen independent mutants were constructed according to all the mutation sites in these three mutants. After transglycosylation analysis, Asp714 and Trp773 were identified as key residues for improvement in transglycosylation ability and were chosen for the second round of directed evolution by site-saturation mutagenesis. Two most efficient mutants D714T and W773R that acted as trans-β-N-acetylhexosaminidase were finally achieved. D714T with the substitution at the putative nucleophile assistant residue Asp714 by threonine showed high yield of 84.7% with unobserved hydrolysis towards transglycosylation product. W773R with arginine substitution at Trp773 residue locating at the entrance of catalytic cavity led to the yield up to 81.8%. The kcat/Km values of D714T and W773R for hydrolysis of pNP-β-GlcNAc displayed drastic decreases. NMR investigation of protein-substrate interaction revealed an invariable mode of the catalytic cavity of D714T, W773R, and WT BbhI. The collective motions of protein model showed the mutations Thr714 and Arg773 exerted little effect on the dynamics of the inside but a large effect on the dynamics of the outside of catalytic cavity.
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Affiliation(s)
- Xiaodi Chen
- State Key Lab of Microbial Technology, National Glycoengineering Research Center, Shandong Provincial Key Laboratory of Carbohydrate Chemistry and Glycobiology, Shandong University, Qingdao, 266237, People's Republic of China.,School of Pharmaceutical Sciences, Shandong University, Jinan, 250012, People's Republic of China
| | - Lan Jin
- State Key Lab of Microbial Technology, National Glycoengineering Research Center, Shandong Provincial Key Laboratory of Carbohydrate Chemistry and Glycobiology, Shandong University, Qingdao, 266237, People's Republic of China
| | - Xukai Jiang
- State Key Lab of Microbial Technology, National Glycoengineering Research Center, Shandong Provincial Key Laboratory of Carbohydrate Chemistry and Glycobiology, Shandong University, Qingdao, 266237, People's Republic of China
| | - Longcheng Guo
- State Key Lab of Microbial Technology, National Glycoengineering Research Center, Shandong Provincial Key Laboratory of Carbohydrate Chemistry and Glycobiology, Shandong University, Qingdao, 266237, People's Republic of China
| | - Guofeng Gu
- State Key Lab of Microbial Technology, National Glycoengineering Research Center, Shandong Provincial Key Laboratory of Carbohydrate Chemistry and Glycobiology, Shandong University, Qingdao, 266237, People's Republic of China
| | - Li Xu
- State Key Lab of Microbial Technology, National Glycoengineering Research Center, Shandong Provincial Key Laboratory of Carbohydrate Chemistry and Glycobiology, Shandong University, Qingdao, 266237, People's Republic of China
| | - Lili Lu
- School of Pharmacy, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, People's Republic of China
| | - Fengshan Wang
- School of Pharmaceutical Sciences, Shandong University, Jinan, 250012, People's Republic of China
| | - Min Xiao
- State Key Lab of Microbial Technology, National Glycoengineering Research Center, Shandong Provincial Key Laboratory of Carbohydrate Chemistry and Glycobiology, Shandong University, Qingdao, 266237, People's Republic of China.
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Yang S, Song S, Yan Q, Fu X, Jiang Z, Yang X. Biochemical characterization of the first fungal glycoside hydrolyase family 3 β-N-acetylglucosaminidase from Rhizomucor miehei. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2014; 62:5181-90. [PMID: 24811866 DOI: 10.1021/jf500912b] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A novel β-N-acetylglucosaminidase gene (RmNag) from Rhizomucor miehei was cloned and expressed in Escherichia coli. RmNag shares the highest identity of 37% with a putative β-N-acetylglucosaminidase from Aspergillus clavatus. The recombinant enzyme was purified to homogeneity. The optimal pH and temperature of RmNag were pH 6.5 and 50 °C, respectively. It was stable in the pH range 6.0-8.0 and at temperatures below 45 °C. RmNag exhibited strict substrate specificity for p-nitrophenyl β-N-acetylglucosaminide (pNP-GlcNAc) and N-acetyl chitooligosaccharides. The apparent Km of RmNag toward pNP-GlcNAc was 0.13 mM. The purified enzyme displayed an exo-type manner as it released the only end product of GlcNAc from all the tested N-acetyl chitooligosaccharides. Besides, RmNag exhibited relatively high N-acetyl-β-D-glucosaminide tolerance with an inhibition constant Ki value of 9.68 mM. The excellent properties may give the enzyme great potential in industries. This is the first report on a glycoside hydrolyase family 3 β-N-acetylglucosaminidase from a fungus.
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Affiliation(s)
- Shaoqing Yang
- Department of Biotechnology, College of Food Science and Nutritional Engineering, and ‡Bioresource Utilization Laboratory, College of Engineering, China Agricultural University , Beijing 100083, China
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Loft KJ, Bojarová P, Slámová K, Kren V, Williams SJ. Synthesis of sulfated glucosaminides for profiling substrate specificities of sulfatases and fungal beta-N-acetylhexosaminidases. Chembiochem 2009; 10:565-76. [PMID: 19156788 DOI: 10.1002/cbic.200800656] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Systematic sulfation: Sulfated glycoconjugates are degraded either by desulfation followed by glycoside cleavage, or by glycoside cleavage followed by desulfation. To study these processes, here we report the synthesis of four regioisomerically sulfated p-nitrophenyl glucosaminides from the common precursor p-nitrophenyl N-acetyl-beta-D-glucosaminide. These substrates allowed the rapid analysis of the substrate preferences of a set of four sulfatases and 24 hexosaminidases.Sulfated carbohydrates are components of many glycoconjugates, and are degraded by two major processes: cleavage of the sulfate ester by a sulfatase, or en bloc removal of a sulfated monosaccharide by a glycoside hydrolase. However, these processes have proved difficult to study owing to a lack of homogeneous, defined substrates. We describe here the synthesis of a series of p-nitrophenyl beta-D-glucosaminides bearing sulfate esters at the 2-, 3-, 4- or 6-positions, by divergent routes starting with p-nitrophenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside. The sulfated p-nitrophenyl beta-D-glucosaminides were used to study the substrate specificity of four sulfatases (from Helix pomatia, Patella vulgata, abalone, and Pseudomonas aeruginosa), and revealed significant differences in the preference of each of these enzymes for desulfation at different positions around the sugar ring. The 3-, 4- and 6-sulfated p-nitrophenyl 2-acetamido-2-deoxy-beta-D-glucosaminides were screened against a panel of 24 fungal beta-N-acetylhexosaminidases to assess their substrate specificity. While the 4- and 6-sulfates were substrates for many of the fungal enzymes investigated, only a single beta-N-acetylhexosaminidase, that from Penicillium chrysogenum, could hydrolyze the 3-sulfated p-nitrophenyl glycoside. Together these results demonstrate the utility of sulfated p-nitrophenyl beta-D-glucosaminides for the study of both sulfatases and glycoside hydrolases.
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Affiliation(s)
- Karen J Loft
- School of Chemistry and Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
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