title: Novel modular enzymes encoded by a cellulase gene cluster in Cellvibrio mixtus.
abstract: Hydrolysis of plant cell wall polysaccharides, a process which is of intrinsic biological and biotechnological importance, requires the concerted action of an extensive repertoire of microbial cellulases and hemicellulases. Here, we report the identification of the gene cluster unk16A, regA and cel5B in the aerobic soil bacterium Cellvibrio mixtus, encoding a family 16 (CmUnk16A) glycoside hydrolase (GH), an AraC/XylS transcription activator (CmRegA) and a family 5 (CmCel5B) endo-glucanase, respectively. CmUnk16A is a modular enzyme comprising, in addition to the catalytic domain, two family 32 carbohydrate-binding modules (CBMs), termed CBM32-1 and CBM32-2, a CBM4 and a domain of unknown function. We show that CBM32-2 binds weakly to laminarin and pustulan. CmRegA is also a modular protein containing a highly hydrophobic N-terminal domain and a C-terminal DNA-binding domain of the AraC/XylS family. The role of the identified enzymes in the hydrolysis of cell wall polysaccharides by aerobic bacteria is discussed.
authors.affiliation: CIISA-Faculdade de Medicina Veterinária, Pólo Universitário do Alto da Ajuda, Avenida da Universidade Tecnica, 1300-477 Lisbon, Portugal.
authors.forename: Maria S J
authors.initials: MS
authors.lastname: Centeno
authors.forename: Arun
authors.initials: A
authors.lastname: Goyal
authors.forename: José A M
authors.initials: JA
authors.lastname: Prates
authors.forename: Luís M A
authors.initials: LM
authors.lastname: Ferreira
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Gilbert
authors.forename: Carlos M G A
authors.initials: CM
authors.lastname: Fontes
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D002473:Cell Wall / Q000201:enzymology / Q000378:metabolism; D002480:Cellulase / Q000235:genetics* / Q000378:metabolism; D020633:Cellvibrio / Q000201:enzymology* / Q000235:genetics*; D003001:Cloning, Molecular; D005936:Glucans; D008969:Molecular Sequence Data; D005810:Multigene Family; D011134:Polysaccharides / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D005936:Glucans; D011134:Polysaccharides; C072722:RegA protein, Bacteria; C002076:pustulan; C008247:laminaran; D002480:Cellulase