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Identification of a functionally important carboxyl group in cellobiohydrolase I from Trichoderma reesei
Author(s) -
Tomme Peter,
Claeyssens Marc
Publication year - 1989
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(89)80136-x
Subject(s) - trichoderma reesei , chemistry , active site , residue (chemistry) , biochemistry , amino acid , stereochemistry , glutamic acid , lysozyme , peptide , peptide sequence , enzyme , cellulase , gene
Several aspects of the specific modification of cellobiohydrolase I (CBH I) from Trichoderma reesei with Woodward's reagent K ( N ‐ethyl‐5‐phenylisoxazolium‐3′‐sulfonate) are presented. The pH dependence of the resulting inactivation points to the implication of an ionising group with a p K a of approx. 5.5. The rapid inactivation kinetics, the specific protection and the stoichiometry of modification (3 versus 2 residues), together with the isolation and amino acid sequencing of the putative active site peptide, provide a large body of evidence for the presence of a catalytically important carboxyl residue in the 125–135 region of the CBH I amino acid sequence. From the striking homology between this peptide sequence and those of the active site regions of different lysozymes, glutamic acid 126 is retained as the most plausible catalytic residue (proton donor) in CBH I, equivalent to glutamic acid 35 in hen egg white lysozyme. Glutamic acid 127 is proposed as a potential active site residue to the homologous endoglucanase I (EG I) isolated from the same Trichoderma species.