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Mathew GM, Madhavan A, Arun KB, Sindhu R, Binod P, Singhania RR, Sukumaran RK, Pandey A. Thermophilic Chitinases: Structural, Functional and Engineering Attributes for Industrial Applications. Appl Biochem Biotechnol 2020; 193:142-164. [PMID: 32827066 DOI: 10.1007/s12010-020-03416-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2020] [Accepted: 08/12/2020] [Indexed: 02/07/2023]
Abstract
Chitin is the second most widely found natural polymer next to cellulose. Chitinases degrade the insoluble chitin to bioactive chitooligomers and monomers for various industrial applications. Based on their function, these enzymes act as biocontrol agents against pathogenic fungi and invasive pests compared with conventional chemical fungicides and insecticides. They have other functional roles in shellfish waste management, fungal protoplast generation, and Single-Cell Protein production. Among the chitinases, thermophilic and thermostable chitinases are gaining popularity in recent years, as they can withstand high temperatures and maintain the enzyme stability for longer periods. Not all chitinases are thermostable; hence, tailor-made thermophilic chitinases are designed to enhance their thermostability by direct evolution, genetic engineering involving mutagenesis, and proteomics approach. Although research has been done extensively on cloning and expression of thermophilic chitinase genes, there are only few papers discussing on the mechanism of chitin degradation using thermophiles. The current review discusses the sources of thermophilic chitinases, improvement of protein stability by gene manipulation, metagenomics approaches, chitin degradation mechanism in thermophiles, and their prospective applications for industrial, agricultural, and pharmaceutical purposes.
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Affiliation(s)
- Gincy M Mathew
- Microbial Processes and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Trivandrum, 695 019, India
| | - Aravind Madhavan
- Rajiv Gandhi Center for Biotechnology, Jagathy, Thiruvananthapuram, 695 014, India
| | - K B Arun
- Rajiv Gandhi Center for Biotechnology, Jagathy, Thiruvananthapuram, 695 014, India
| | - Raveendran Sindhu
- Microbial Processes and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Trivandrum, 695 019, India
| | - Parameswaran Binod
- Microbial Processes and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Trivandrum, 695 019, India
| | | | - Rajeev K Sukumaran
- Microbial Processes and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Trivandrum, 695 019, India
| | - Ashok Pandey
- Center for Innovation and Translational Research, CSIR - Indian Institute of Toxicology Research, Lucknow, 226 001, India.
- Frontier Research Lab, Yonsei University, Seoul, South Korea.
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Marine chitinolytic enzymes, a biotechnological treasure hidden in the ocean? Appl Microbiol Biotechnol 2018; 102:9937-9948. [PMID: 30276711 DOI: 10.1007/s00253-018-9385-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 09/04/2018] [Accepted: 09/06/2018] [Indexed: 12/11/2022]
Abstract
Chitinolytic enzymes are capable to catalyze the chitin hydrolysis. Due to their biomedical and biotechnological applications, nowadays chitinolytic enzymes have attracted worldwide attention. Chitinolytic enzymes have provided numerous useful materials in many different industries, such as food, pharmaceutical, cosmetic, or biomedical industry. Marine enzymes are commonly employed in industry because they display better operational properties than animal, plant, or bacterial homologs. In this mini-review, we want to describe marine chitinolytic enzymes as versatile enzymes in different biotechnological fields. In this regard, interesting comments about their biological role, reaction mechanism, production, functional characterization, immobilization, and biotechnological application are shown in this work.
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Fan XJ, Yang C, Zhang C, Ren H, Zhang JD. Cloning, Site-Directed Mutagenesis, and Functional Analysis of Active Residues in Lymantria dispar Chitinase. Appl Biochem Biotechnol 2017; 184:12-24. [PMID: 28577192 DOI: 10.1007/s12010-017-2524-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2016] [Accepted: 05/23/2017] [Indexed: 10/19/2022]
Abstract
Chitinases are glycosyl hydrolases that catalyze the hydrolysis of β-(1,4)-glycosidic bonds in chitin, the major structural polysaccharide presented in the cuticle and gut peritrophic matrix of insects. Two aspartate residues (D143, D145) and one tryptophan (W146) in the Lymantria dispar chitinase are highly conserved residues observed within the second conserved motif of the family 18 chitinase catalytic region. In this study, a chitinase cDNA, LdCht5, was cloned from L. dispar, and the roles of the three residues were investigated using site-directed mutagenesis and substituting them with three other amino acids. Seven mutant proteins, D143E, D145E, W146G, D143E/D145E, D143E/W146G, D145E/W146G, and D143E/D145E/W146G, as well as the wild-type enzyme, were produced using the baculovirus-insect cell line expression system. The enzymatic and kinetic properties of these mutant enzymes were measured using the oligosaccharide substrate MU-(GlcNAc)3. Among the seven mutants, the D145E, D143E/D145E, and D145E/W146G mutations kept some extant catalytic activity toward MU-(GlcNAc)3, while the D143E, W146G, D143E/W146G, and D143E/D145E/W146G mutant enzymes were inactivated. Compared with the mutant enzymes, the wild-type enzyme had higher values of k cat and k cat / K m . A study of the multiple point mutations in the second conserved catalytic region would help to elucidate the role of the critical residues and their relationships.
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Affiliation(s)
- Xiao-Jun Fan
- Department of Biological and Pharmaceutical Engineering, College of Chemistry and Chemical Engineering, Taiyuan University of Technology, No. 79 West Yingze Street, Taiyuan, Shanxi, 030024, People's Republic of China
| | - Chun Yang
- Department of Biological and Pharmaceutical Engineering, College of Chemistry and Chemical Engineering, Taiyuan University of Technology, No. 79 West Yingze Street, Taiyuan, Shanxi, 030024, People's Republic of China
| | - Chang Zhang
- Department of Biological and Pharmaceutical Engineering, College of Chemistry and Chemical Engineering, Taiyuan University of Technology, No. 79 West Yingze Street, Taiyuan, Shanxi, 030024, People's Republic of China
| | - Hui Ren
- Department of Biological and Pharmaceutical Engineering, College of Chemistry and Chemical Engineering, Taiyuan University of Technology, No. 79 West Yingze Street, Taiyuan, Shanxi, 030024, People's Republic of China
| | - Jian-Dong Zhang
- Department of Biological and Pharmaceutical Engineering, College of Chemistry and Chemical Engineering, Taiyuan University of Technology, No. 79 West Yingze Street, Taiyuan, Shanxi, 030024, People's Republic of China.
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de la Fuente-Salcido NM, Casados-Vázquez LE, García-Pérez AP, Barboza-Pérez UE, Bideshi DK, Salcedo-Hernández R, García-Almendarez BE, Barboza-Corona JE. The endochitinase ChiA Btt of Bacillus thuringiensis subsp. tenebrionis DSM-2803 and its potential use to control the phytopathogen Colletotrichum gloeosporioides. Microbiologyopen 2016; 5:819-829. [PMID: 27173732 PMCID: PMC5061718 DOI: 10.1002/mbo3.372] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Revised: 03/21/2016] [Accepted: 03/30/2016] [Indexed: 01/09/2023] Open
Abstract
Bacillus thuringiensis subsp. tenebrionis DSM‐2803 has been studied extensively and spore/crystal mixtures of this strain are used widely in commercial products to control coleopteran pests. The endochitinase chiA Btt gene of B. thuringiensis subsp. tenebrionis DSM‐2803 was cloned and expressed in Escherichia coli. The recombinant 6x‐histidine tagged protein (rChiA Btt, ~74 kDa), was purified by a HiTrap Ni affinity column. The Km of rChiA Btt was 0.847 μmol L−1 and its optimal activity occurred at pH 7 and ~40°C. Most divalent cations reduced endochitinase activity but only Hg+2 abolished activity of the enzyme. We report for the first time the characterization of a chitinase synthesized by B. thuringiensis subsp. tenebrionis DSM‐2803, and show that the purified rChiA74 Btt reduced the radial growth and increased the hyphal density of Colletotrichium gloeosporioides, the etiological agent of “anthracnose” in plants.
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Affiliation(s)
- Norma M de la Fuente-Salcido
- Aniversidad Autónoma de Coahuila, Escuela de Ciencias Biológicas, Torreón, Coahuila, 27104, México.,Posgrado en Biociencias, División de Ciencias de la Vida, Universidad de Guanajuato Campus Irapuato-Salamanca, Irapuato, Guanajuato, 36500, México
| | - Luz E Casados-Vázquez
- Posgrado en Biociencias, División de Ciencias de la Vida, Universidad de Guanajuato Campus Irapuato-Salamanca, Irapuato, Guanajuato, 36500, México.,Departamento de Alimentos, División de Ciencias de la Vida, Universidad de Guanajuato Campus Irapuato-Salamanca, Irapuato, Guanajuato, 36500, México
| | - Ada P García-Pérez
- Aniversidad Autónoma de Coahuila, Escuela de Ciencias Biológicas, Torreón, Coahuila, 27104, México
| | - Uriel E Barboza-Pérez
- Tecnológico de Monterrey Campus Querétaro, Epigmenio González 500 Fracc, San Pablo, Querétaro, Qro, 76130, México
| | - Dennis K Bideshi
- Department of Natural and Mathematical Sciences, California Baptist University, 8432 Magnolia Avenue, Riverside, 92504, California.,Department of Entomology, University of California, Riverside, California, 92521
| | - Rubén Salcedo-Hernández
- Posgrado en Biociencias, División de Ciencias de la Vida, Universidad de Guanajuato Campus Irapuato-Salamanca, Irapuato, Guanajuato, 36500, México.,Departamento de Alimentos, División de Ciencias de la Vida, Universidad de Guanajuato Campus Irapuato-Salamanca, Irapuato, Guanajuato, 36500, México
| | | | - José E Barboza-Corona
- Posgrado en Biociencias, División de Ciencias de la Vida, Universidad de Guanajuato Campus Irapuato-Salamanca, Irapuato, Guanajuato, 36500, México. .,Departamento de Alimentos, División de Ciencias de la Vida, Universidad de Guanajuato Campus Irapuato-Salamanca, Irapuato, Guanajuato, 36500, México.
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Heterologous expression, purification and biochemical characterization of endochitinase ChiA74 from Bacillus thuringiensis. Protein Expr Purif 2014; 109:99-105. [PMID: 25478931 DOI: 10.1016/j.pep.2014.11.015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Revised: 11/12/2014] [Accepted: 11/21/2014] [Indexed: 01/30/2023]
Abstract
ChiA74 is a secreted endochitinase produced by Bacillus thuringiensis. Previously we have partially characterized the physical parameters that affect enzymatic activity of ChiA74 in crude preparations of bacterial secretomes. In the present study, we cloned the chiA74 open reading frame (ORF) lacking the 5' sequence coding for its secretion signal peptide (chiA74Δsp) into a cold shock expression vector (pColdI) for production of the enzyme in Escherichia coli BL21-Rosetta 2. As a result, the N-terminal end of ChiA74Δsp ORF was fused to an artificial sequence of 28 amino acid, including a 6× histidine tag for purification of recombinant 6×His tagged-ChiA74Δsp (rChiA74, ∼74kDa). Along with a protein of ∼74kDa, we co-purified its ∼55kDa processed form which was confirmed by Western blot analysis. Optimal endochitinase activity of purified rChiA74 occurred at pH 7 and 40°C. Most divalent cations (e.g. Ba(+2), Ca(+2), Mn(+2), Mg(+2), Zn(+2) and Cu(+2)) at concentration of 10mM reduced chitinase activity by ∼30%, and Hg(+2) (10mM) drastically inhibited ChiA74 activity by ∼75-100%. The Vmax, Km and kcat for rChiA74 were 0.11±0.01nmol/min, 2.15μM±0.45 and 3.81s(-1), respectively, using 4-MU-GlcNAc3 as substrate. Using purified rChiA74 and colloidal chitin as substrate, chitin-derived oligosaccharides with degree of polymerization of 2 and 1 were detected.
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Neeraja C, Anil K, Purushotham P, Suma K, Sarma P, Moerschbacher BM, Podile AR. Biotechnological approaches to develop bacterial chitinases as a bioshield against fungal diseases of plants. Crit Rev Biotechnol 2010; 30:231-41. [PMID: 20572789 DOI: 10.3109/07388551.2010.487258] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Fungal diseases of plants continue to contribute to heavy crop losses in spite of the best control efforts of plant pathologists. Breeding for disease-resistant varieties and the application of synthetic chemical fungicides are the most widely accepted approaches in plant disease management. An alternative approach to avoid the undesired effects of chemical control could be biological control using antifungal bacteria that exhibit a direct action against fungal pathogens. Several biocontrol agents, with specific fungal targets, have been registered and released in the commercial market with different fungal pathogens as targets. However, these have not yet achieved their full commercial potential due to the inherent limitations in the use of living organisms, such as relatively short shelf life of the products and inconsistent performance in the field. Different mechanisms of action have been identified in microbial biocontrol of fungal plant diseases including competition for space or nutrients, production of antifungal metabolites, and secretion of hydrolytic enzymes such as chitinases and glucanases. This review focuses on the bacterial chitinases that hydrolyze the chitinous fungal cell wall, which is the most important targeted structural component of fungal pathogens. The application of the hydrolytic enzyme preparations, devoid of live bacteria, could be more efficacious in fungal control strategies. This approach, however, is still in its infancy, due to prohibitive production costs. Here, we critically examine available sources of bacterial chitinases and the approaches to improve enzymatic properties using biotechnological tools. We project that the combination of microbial and recombinant DNA technologies will yield more effective environment-friendly products of bacterial chitinases to control fungal diseases of crops.
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Affiliation(s)
- Chilukoti Neeraja
- Department of Plant Sciences, University of Hyderabad, Hyderabad, India
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Functional analysis of active site residues of Bacillus thuringiensis WB7 chitinase by site-directed mutagenesis. World J Microbiol Biotechnol 2009. [DOI: 10.1007/s11274-009-0119-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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Park SK, Kim CW, Kim H, Jung JS, Harman GE. Cloning and high-level production of a chitinase from Chromobacterium sp. and the role of conserved or nonconserved residues on its catalytic activity. Appl Microbiol Biotechnol 2007; 74:791-804. [PMID: 17294188 DOI: 10.1007/s00253-006-0614-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2006] [Revised: 07/17/2006] [Accepted: 08/08/2006] [Indexed: 10/23/2022]
Abstract
A gene encoding an alkaline (pI of 8.67) chitinase was cloned and sequenced from Chromobacterium sp. strain C-61. The gene was composed of 1,611 nucleotides and encoded a signal sequence of 26 N-terminal amino acids and a mature protein of 510 amino acids. Two chitinases of 54 and 52 kDa from both recombinant Escherichia coli and C-61 were detected on SDS-PAGE. Maximum chitinase activity was obtained in the culture supernatant of recombinant E. coli when cultivated in TB medium for 6 days at 37 degrees C and was about fourfold higher than that from C-61. Chi54 from the culture supernatants could be purified by a single step based on isoelectric point. The purified Chi54 had about twofold higher binding affinity to chitin than to cellulose. The chi54 encoded a protein that included a type 3 chitin-binding domain belonging to group A and a family 18 catalytic domain belonging to subfamily A. In the catalytic domain, mutation of perfectly conserved residues and highly conserved residues resulted in loss of nearly all activity, while mutation of nonconserved residues resulted in enzymes that retained activity. In this process, a mutant (T218S) was obtained that had about 133% of the activity of the wild type, based on comparison of K (cat) values.
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Affiliation(s)
- Seur Kee Park
- Department of Agricultural Biology, Sunchon National University, Sunchon, South Korea
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Zhang H, Huang X, Fukamizo T, Muthukrishnan S, Kramer KJ. Site-directed mutagenesis and functional analysis of an active site tryptophan of insect chitinase. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2002; 32:1477-1488. [PMID: 12530215 DOI: 10.1016/s0965-1748(02)00068-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Chitinase is an enzyme used by insects to degrade the structural polysaccharide, chitin, during the molting process. Tryptophan 145 (W145) of Manduca sexta (tobacco hornworm) chitinase is a highly conserved residue found within a second conserved region of family 18 chitinases. It is located between aspartate 144 (D144) and glutamate 146 (E146), which are putative catalytic residues. The role of the active site residue, W145, in M. sexta chitinase catalysis was investigated by site-directed mutagenesis. W145 was mutated to phenylalanine (F), tyrosine (Y), isoleucine (I), histidine (H), and glycine (G). Wild-type and mutant forms of M. sexta chitinases were expressed in a baculovirus-insect cell line system. The chitinases secreted into the medium were purified and characterized by analyzing their catalytic activity and substrate or inhibitor binding properties. The wild-type chitinase was most active in the alkaline pH range. Several of the mutations resulted in a narrowing of the range of pH over which the enzyme hydrolyzed the polymeric substrate, CM-Chitin-RBV, predominantly on the alkaline side of the pH optimum curve. The range was reduced by about 1 pH unit for W145I and W145Y and by about 2 units for W145H and W145F. The W145G mutation was inactive. Therefore, the hydrophobicity of W145 appears to be critical for maintaining an abnormal pKa of a catalytic residue, which extends the activity further into the alkaline range. All of the mutant enzymes bound to chitin, suggesting that W145 was not essential for binding to chitin. However, the small difference in Km's of mutated enzymes compared to Km values of the wild-type chitinase towards both the oligomeric and polymeric substrates suggested that W145 is not essential for substrate binding but probably influences the ionization of a catalytically important group(s). The variations in kcat's among the mutated enzymes and the IC50 for the transition state inhibitor analog, allosamidin, indicate that W145 also influences formation of the transition state during catalysis.
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Affiliation(s)
- Hong Zhang
- Department of Biochemistry, Kansas State University, Manhattan, Kansas 66506, USA
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Lu Y, Zen KC, Muthukrishnan S, Kramer KJ. Site-directed mutagenesis and functional analysis of active site acidic amino acid residues D142, D144 and E146 in Manduca sexta (tobacco hornworm) chitinase. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2002; 32:1369-1382. [PMID: 12530205 DOI: 10.1016/s0965-1748(02)00057-7] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Chitinases (EC 3.2.1.14) are glycosyl hydrolases that catalyze the hydrolysis of beta-(1, 4)-glycosidic bonds in chitin, the major structural polysaccharide present in the cuticle and gut peritrophic matrix of insects. Two conserved regions have been identified from amino acid sequence comparisons of family 18 glycosyl hydrolases, which includes Manduca sexta (tobacco hornworm) chitinase as a member. The second of these regions in M. sexta chitinase contains three very highly conserved acidic amino acid residues, D142, D144 and E146, that are probably active site residues. In this study the functional roles of these three residues were investigated using site-directed mutagenesis for their substitutions to other amino acids. Six mutant proteins, D142E, D142N, D144E, D144N, E146D and E146Q, as well as the wild-type enzyme, were produced using a baculovirus-insect cell line expression system. The proteins were purified by anion-exchange chromatography, after which their physical, kinetic and substrate binding properties were determined. Circular dichroism spectra of the mutant proteins were similar to that of the wild-type protein, indicating that the presence of mutations did not change the overall secondary structures. E146 was required for enzymatic activity because mutants E146Q and E146D were devoid of activity. D144E retained most of the enzymatic activity, but D144N lost nearly 90%. There was a shift in the pH optimum from alkaline pH to acidic pH for mutants D142N and D144E with minimal losses of activity relative to the wild-type enzyme. The pH-activity profile for the D142E mutation resembled that of the wild-type enzyme except activity in the neutral and acidic range was lower. All of the mutant proteins bound to chitin. Therefore, none of these acidic residues was essential for substrate binding. The results indicate that E146 probably functions as an acid/base catalyst in the hydrolytic mechanism, as do homologous residues in other glycosyl hydrolases. D144 apparently functions as an electrostatic stabilizer of the positively charged transition state, whereas D142 probably influences the pKa values of D144 and E146.
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Affiliation(s)
- Yimin Lu
- Grain Marketing and Production Research Center, ARS, USDA, Manhattan, Kansas 66502, USA
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Varela PF, Llera AS, Mariuzza RA, Tormo J. Crystal structure of imaginal disc growth factor-2. A member of a new family of growth-promoting glycoproteins from Drosophila melanogaster. J Biol Chem 2002; 277:13229-36. [PMID: 11821393 DOI: 10.1074/jbc.m110502200] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Imaginal disc growth factor-2 (IDGF-2) is a member of a recently described family of Drosophila melanogaster-soluble polypeptide growth factors that promote cell proliferation in imaginal discs. Although their precise mode of action has not been established, IDGFs cooperate with insulin in stimulating the growth of imaginal disc cells. We report the crystal structure of IDGF-2 at 1.3-A resolution. The structure shows the classical (betaalpha)(8) barrel-fold of family 18 glycosyl hydrolases, with an insertion of an alpha + beta domain similar to that of Serratia marcescens chitinases A and B. However, amino acid substitutions in the consensus catalytic sequence of chitinases give IDGF-2 a less negatively charged environment in its putative ligand-binding site and preclude the nucleophilic attack mechanism of chitin hydrolysis. Particularly important is the replacement of Glu by Gln at position 132, which has been shown to abolish enzymatic activity in chitinases. Nevertheless, a modest conservation of residues that participate in oligosaccharide recognition suggests that IDGF-2 could bind carbohydrates, assuming several conformational changes to open the partially occluded binding site. Thus, IDGFs may have evolved from chitinases to acquire new functions as growth factors, interacting with cell surface glycoproteins implicated in growth-promoting processes, such as the Drosophila insulin receptor.
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Affiliation(s)
- Paloma F Varela
- Center for Advanced Research in Biotechnology, W. M. Keck Laboratory of Structural Biology, University of Maryland Biotechnology Institute, Rockville, MD 20850, USA
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Bokma E, Rozeboom HJ, Sibbald M, Dijkstra BW, Beintema JJ. Expression and characterization of active site mutants of hevamine, a chitinase from the rubber tree Hevea brasiliensis. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:893-901. [PMID: 11846790 DOI: 10.1046/j.0014-2956.2001.02721.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Hevamine is a chitinase from the rubber tree Hevea brasiliensis. Its active site contains Asp125, Glu127, and Tyr183, which interact with the -1 sugar residue of the substrate. To investigate their role in catalysis, we have successfully expressed wild-type enzyme and mutants of these residues as inclusion bodies in Escherichia coli. After refolding and purification they were characterized by both structural and enzyme kinetic studies. Mutation of Tyr183 to phenylalanine produced an enzyme with a lower k(cat) and a slightly higher K(m) than the wild-type enzyme. Mutating Asp125 and Glu127 to alanine gave mutants with approximately 2% residual activity. In contrast, the Asp125Asn mutant retained substantial activity, with an approximately twofold lower k(cat) and an approximately twofold higher K(m) than the wild-type enzyme. More interestingly, it showed activity to higher pH values than the other variants. The X-ray structure of the Asp125Ala/Glu127Ala double mutant soaked with chitotetraose shows that, compared with wild-type hevamine, the carbonyl oxygen atom of the N-acetyl group of the -1 sugar residue has rotated away from the C1 atom of that residue. The combined structural and kinetic data show that Asp125 and Tyr183 contribute to catalysis by positioning the carbonyl oxygen of the N-acetyl group near to the C1 atom. This allows the stabilization of a positively charged transient intermediate, in agreement with a previous proposal that the enzyme makes use of substrate-assisted catalysis.
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Affiliation(s)
- Evert Bokma
- Department of Biochemistry, Rijksuniversiteit Groningen, The Netherlands.
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