title: Cel6A, a major exoglucanase from the cellulosome of the anaerobic fungi Piromyces sp. E2 and Piromyces equi.
abstract: Anaerobic fungi possess high cellulolytic activities, which are organised in high molecular mass (HMM) complexes. Besides catalytic modules, the cellulolytic enzyme components of these complexes contain non-catalytic modules, known as dockerins, that play a key role in complex assembly. Screening of a genomic and a cDNA library of two Piromyces species resulted in the isolation of two clones containing inserts of 5.5 kb (Piromyces sp. E2) and 1.5 kb (Piromyces equi). Both clones contained the complete coding region of a glycoside hydrolase (GH) from family 6, consisting of a 20 amino acid signal peptide, a 76 (sp. E2)/81 (P. equi) amino acid stretch comprising two fungal non-catalytic docking domains (NCDDs), a 24 (sp. E2)/16 (P. equi) amino acid linker, and a 369 amino acid catalytic module. Homology modelling of the catalytic module strongly suggests that the Piromyces enzymes will be processive cellobiohydrolases. The catalytic residues and all nearby residues are conserved. The reaction is thus expected to proceed via a classical single-displacement (inverting) mechanism that is characteristic of this family of GHs. The enzyme, defined as Cel6A, encoded by the full-length Piromyces E2 sequence was expressed in Escherichia coli. The recombinant protein expressed had a molecular mass of 55 kDa and showed activity against Avicel, supporting the observed relationship of the sequence to those of known cellobiohydrolases. Affinity-purified cellulosomes of Piromyces sp. E2 were analysed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) electrophoresis. A major band was detected with the molecular weight of Cel6A. A tryptic fingerprint of this protein confirmed its identity.
authors.affiliation: Department of Microbiology, Faculty of Science, University of Nijmegen, Toernooiveld 1, NL-6525 ED, Nijmegen, The Netherlands.
authors.forename: Harry R
authors.initials: HR
authors.lastname: Harhangi
authors.forename: Alexander C J
authors.initials: AC
authors.lastname: Freelove
authors.forename: Wimal
authors.initials: W
authors.lastname: Ubhayasekera
authors.forename: Maarten
authors.initials: M
authors.lastname: van Dinther
authors.forename: Peter J M
authors.initials: PJ
authors.lastname: Steenbakkers
authors.forename: Anna
authors.initials: A
authors.lastname: Akhmanova
authors.forename: Chris
authors.initials: C
authors.lastname: van der Drift
authors.forename: Mike S M
authors.initials: MS
authors.lastname: Jetten
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Mowbray
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Gilbert
authors.forename: Huub J M
authors.initials: HJ
authors.lastname: Op den Camp
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D002480:Cellulase / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D043366:Cellulose 1,4-beta-Cellobiosidase; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D015723:Gene Library; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D020089:Piromyces / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014357:Trypsin / Q000494:pharmacology
chemical_list: D018076:DNA, Complementary; D005656:Fungal Proteins; D011994:Recombinant Proteins; D002480:Cellulase; D043366:Cellulose 1,4-beta-Cellobiosidase; D014357:Trypsin