Primary sequence and enzymic properties of two modular endoglucanases, Cel5A and Cel45A, from the anaerobic fungus Piromyces equi.
Two endoglucanase cDNAs, designated cel5A and cel45A, were isolated from a cDNA library of the anaerobic fungus Piromyces equi. Sequence analysis revealed that cel5A has an open reading frame of 5142 bp and encodes a 1714 amino acid modular enzyme, Cel5A, with a molecular mass of 194847 Da. Cel5A consists of four catalytic domains homologous to family-5 glycosyl hydrolases, two C-terminal dockerins and one N-terminal dockerin. This is the first report of a complete gene containing tandem repeats of family-5 catalytic domains. The cDNA cel45A has an open reading frame of 1233 bp and encodes a 410 amino acid modular enzyme, Cel45A, with a molecular mass of 44380 Da. The catalytic domain, located at the C terminus, is homologous to the family-45 glycosyl hydrolases. Cel45A is the first family-45 enzyme to be described in an anaerobe. The presence of dockerins at the N and C termini of Cel5A and at the N terminus of Cel45A implies that both enzymes are part of the high-molecular-mass cellulose-degrading complex produced by Piromyces equi. The catalytic domain nearest the C terminus of Cel5A and the catalytic domain of Cel45A were hyperexpressed as thioredoxin fusion proteins, Trx-Cel5A' and Trx-Cel45A', and subjected to biochemical analysis. Trx-Cel5A' has a broad substrate range, showing activity against carboxymethylcellulose, acid-swollen cellulose, barley beta-glucan, lichenin, carob galactomannan, p-nitrophenyl beta-D-cellobiopyranoside and xylan. Trx-Cel45A' is active against carboxymethylcellulose, acid-swollen cellulose and the mixed linkage glucans, barley beta-glucan and lichenin.
Laboratory of Molecular Enzymology, The Babraham Institute, Babraham, Cambridge CB2 4AT, UK1.
Ruth Y
RY
Eberhardt
Department of Biological and Nutritional Sciences, The University of Newcastle upon Tyne, Newcastle upon Tyne NE1 7RU, UK2.
Harry J
HJ
Gilbert
Laboratory of Molecular Enzymology, The Babraham Institute, Babraham, Cambridge CB2 4AT, UK1.
Geoffrey P
GP
Hazlewood
D000595:Amino Acid Sequence; D001483:Base Sequence; D020134:Catalytic Domain / Q000235:genetics; D002480:Cellulase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D004271:DNA, Fungal / Q000235:genetics / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D008970:Molecular Weight; D020089:Piromyces / Q000201:enzymology* / Q000235:genetics*; D017434:Protein Structure, Tertiary / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D017931:DNA Primers; D018076:DNA, Complementary; D004271:DNA, Fungal; C407024:endoglucanase Cel5A; D002480:Cellulase