Structure of cellulases from the fungus Aspergillus niger and a wood-eating termite /
Cellulose is the major component of wood. Cellulases degrade the cellulose polymer by cleaving the glycosidic linkage between glucose monomers. Cellulases can be either useful, by producing energy from cellulose degradation, or harmful, by destruction of structural wood. Here, we report the 3D struc...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2001.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=725911901&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Cellulose is the major component of wood. Cellulases degrade the cellulose polymer by cleaving the glycosidic linkage between glucose monomers. Cellulases can be either useful, by producing energy from cellulose degradation, or harmful, by destruction of structural wood. Here, we report the 3D structures of two endo-β-1,4-glucanase, the main component of cellulases, from fungus, Aspergillus niger (EglA) and the other from a wood-eating termite, Nasutitermes takasagoensis (NtEgl). EglA, a member of glycosyl hydrolase of family 12, has a retaining mechanism. The structure of EglA, determined at 2.1 [Å] resolution, has a general 'jelly-roll' folding, which is a characteristic of cellulases from family 12. In spite of very low sequence identity between EglA and CelB2, the other member of family 12, the 3D structures of the core regions are quite similar. The 3D structural comparison shows that conserved Glu 204 is the catalytic acid/base and conserved Glu 116 is the nucleophilic residue. The 3D structural comparison between glycosyl hydrolases from families 11 (xylanase) and 12 (endoglucanase) confirmed that they belong to the same clan, GH-C. The structural differences are mostly found in loop regions. The 3D structural comparison of family 12 and family 11 enzymes suggests that the binding site loops may be determinant for substrate selectivity. NtEgl, determined at 1.55 [Å] resolution, has the general folding of an (α/α)₆ barrel, which is a common folding pattern for family 9. The 3D structural analysis shows that conserved Glu 412 is the catalytic acid/base residue and conserved Asp 54 or Asp 57 is the base. The enzyme has a Ca²[+] binding site near its substrate binding cleft. The comparison between the structure of Ca²[+]-free enzyme, produced by reducing the pH of crystal soaking solution from 5.6 to 2.5, and Ca²[+]-bound enzyme did not show significant differences in location of α-carbon atoms. The main differences are in the conformation of the residues ligating with Ca²[+]. The overall structure of NtEgl at pH's 6.5 is similar to that of pH 5.6 (The optimum pH for enzyme). The major change observed was in the conformation of the side chain of the catalytic acid/base Glu 412. |
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| Item Description: | Vita. "Major Subject: Biochemistry". |
| Physical Description: | xi, 127 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 97-125). |