celA from Bacillus lautus PL236 encodes a novel cellulose-binding endo-beta-1,4-glucanase.
celA from the cellulolytic bacterium Bacillus lautus PL236 encodes EG-A, an endo-beta-1,4-glucanase. An open reading frame of 2,100 bp preceded by a ribosome-binding site encodes a protein with a molecular mass of 76,863 Da with a typical signal sequence. The NH2-terminal active domain of EG-A is not homologous to any reported cellulase or xylanase and may represent a new family of such enzymes. A 150-amino-acid COOH-terminal peptide is homologous to noncatalytic domains in several other cellulases (A. Meinke, N.R. Gilkes, D.G. Kilburn, R.C. Miller, Jr., and R.A.J. Warren, J. Bacteriol. 173:7126-7135, 1991). Upstream of celA, a partial open reading frame encodes a 145-amino-acid peptide which also belongs to the family mentioned. Zymogram analysis of extracts from Escherichia coli and supernatants of Bacillus subtilis and B. megaterium, including protease-deficient mutants thereof, which express celA, revealed two active proteins, EG-A-L and EG-A-S, with Mrs of 74,000 and 57,000, respectively. The proportion of EG-A-L to EG-A-S depends on the extracellular proteolytic activity of the host organism, indicating that EG-A-S arises from posttranslational proteolytic modification of EG-A-L. Since EG-A-S has an NH2 terminus corresponding to the predicted NH2-terminal sequence of EG-A, processing appears to take place between the catalytic and noncatalytic domains described. EG-A-L and EG-A-S were purified to homogeneity and shown to have almost identical characteristics with respect to activity against soluble substrates and pH and temperature dependency. EG-A-L binds strongly to cellulose, in contrast to EG-A-S, and has higher activity against insoluble substrates than the latter. We conclude that the COOH-terminal 17,000-Mr peptide of EG-A-L constitutes a cellulose-binding domain.
Hansen
C K
CK
Unité de Biochimie Microbienne, Institut Pasteur, Paris, France.
Diderichsen
B
B
Jørgensen
P L
PL
D000595:Amino Acid Sequence; D001407:Bacillus / Q000201:enzymology / Q000235:genetics*; D001412:Bacillus subtilis / Q000235:genetics; D001483:Base Sequence; D002480:Cellulase / Q000096:biosynthesis / Q000145:classification / Q000235:genetics*; D002482:Cellulose / Q000378:metabolism; D003001:Cloning, Molecular; D004252:DNA Mutational Analysis; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics; D008969:Molecular Sequence Data; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000096:biosynthesis; D012689:Sequence Homology, Nucleic Acid; D013379:Substrate Specificity
D011994:Recombinant Proteins; D002482:Cellulose; C074775:CelA endoglucanase; D002480:Cellulase