Structure of the Clostridium thermocellum gene licB and the encoded beta-1,3-1,4-glucanase. A catalytic region homologous to Bacillus lichenases joined to the reiterated domain of clostridial cellulases.
The nucleotide sequence of the Clostridium thermocellum gene licB, coding for a thermoactive beta-1,3-1,4-glucanase, has been determined. The gene is located downstream, but in opposite orientation to the beta-glucosidase gene bglA. A coding region of 1002 bp is flanked by canonical promoter and transcription terminator sequences. The primary translation product of the licB gene has a predicted molecular mass of 37,896 Da. The protein sequence can be divided into several discrete segments: an N-terminal signal peptide, a catalytic region, a segment rich in Pro and Thr residues and a C-terminal reiterated domain. The catalytic region shows close similarity to lichenases of bacilli (52-58% identity) and Fibrobacter succinogenes (35% identity), but is unrelated to barley beta-1,3-1,4-glucanases. It consists of two domains, which in the case of the F. succinogenes lichenase are arranged in reversed order to that of C. thermocellum and Bacillus lichenases. The C-terminal reiterated domain of C. thermocellum lichenase is homologous to the duplicated non-catalytic domain of endo-beta-1,4-glucanases and xylanase Z from the same organism. This domain is considered a characteristic feature of clostridial cellulases organized as multienzyme complex (cellulosome). The beta-1,3-1,4-glucanase encoded by the licB gene might therefore be an additional enzyme component of the C. thermocellum cellulosome.
Schimming
S
S
Institute for Microbiology, Technical University Munich, Federal Republic of Germany.
Schwarz
W H
WH
Staudenbauer
W L
WL
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D002480:Cellulase / Q000737:chemistry; D003013:Clostridium / Q000201:enzymology / Q000235:genetics*; D004269:DNA, Bacterial / Q000737:chemistry; D005798:Genes, Bacterial; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid
D004269:DNA, Bacterial; D006026:Glycoside Hydrolases; D002480:Cellulase; C028020:licheninase