Sequence of the cellulase gene ofClostridium thermoceltumcoding for endoglucanase B

Abstract

The nucleotide sequence of the CelB gene, encoding the extracellular endoglucanase B of Clostridium thermocellum, is reported. The putative start of the 1689 bp coding sequence was assigned to an ATG codon which is preceded by an AGGAGG sequence typical of ribosomal binding sites in Gram-positive bacteria. The amino-terminal end of the deduced protein sequence is similar to signal peptides described for other bacterial secretory proteins. The carboxy-terminal ends of endoglucanases A and B appear to be remarkably homologous. A striking feature of the conserved region is that both proteins contain two reiterated stretches of 23 aminoacids each, separated by 9 residues.

Cloning, DNA sequencing, and expression of the gene encoding Clostridium thermocellum cellulase CelJ, the largest catalytic component of the cellulosome

“…This structure is similar to the rho factor-independent terminator of E. coli (37). The codon usage of celJ was generally similar to that reported for other C. thermocellum genes (3,14,17,18,20,28,35,43,50). Interestingly, an incomplete but certain ORF (ORF2) encoding a part of the family E2 catalytic domain was found downstream of celJ.…”

“…Purification of components from a cellulosome fraction revealed that the combination of two proteins, a noncatalytic scaffolding protein variously known as S L , S1, or CipA (11) and an exoglucanase known as S S , S8, or CelS (46), could completely solubilize Avicel but only at very low rates (49), suggesting that some catalytic components other than CelS in the cellulosomes play an important role in the efficient degradation of crystalline cellulose. In this context, various C. thermocellum gene banks were constructed, and at least nine endoglucanase genes (3,14,17,18,20,28,35,43,50) and two xylanase genes (9,15) in addition to cipA and celS, along with their translated products, have been characterized so far. Despite great effort, however, many genes encoding cellulosomal proteins have not yet been identified.…”

Cellulase, Clostridia, and Ethanol

“…CelF, the CelS equivalent in C. cellulolyticum, also displays significant activity in reducing the viscosity of a CMC solution (271). Some of the cloned endoglucanase genes are celA (26), celB (105), celC (298), celD (143,326), celE (113), celF (245), celG (188), celH (361), celI (101,123,373), celJ (encoding component S2 of the complex) (1,8), celM (162), celN (373), celQ (9), celT (172), and celX (113).…”

Characterization of a gene encoding a major .BETA.-endoglucanase from Xanthomonas albilineans.

“…3) of this region from the different endoglucanases, reveals that the two aa(s) which had previously been identified as potentially catalytic in cellulase A (16) are conserved, and positioned as His145 and G1u194 in egxA. Since Henrissat et al (16) has categorized both celB of Clostridium thermocellum (12) and engC from Bacillus subtilis (26) as belonging to family A, and because of their obvious homology to egxA, it is proposed that the X. albilineans endoglucanase egxA gene be classified in this family.…”