title: Functional insights into the role of novel type I cohesin and dockerin domains from Clostridium thermocellum.
abstract: Cellulosomes, synthesized by anaerobic microorganisms such as Clostridium thermocellum, are remarkably complex nanomachines that efficiently degrade plant cell wall polysaccharides. Cellulosome assembly results from the interaction of type I dockerin domains, present on the catalytic subunits, and the cohesin domains of a large non-catalytic integrating protein that acts as a molecular scaffold. In general, type I dockerins contain two distinct cohesin-binding interfaces that appear to display identical ligand specificities. Inspection of the C. thermocellum genome reveals 72 dockerin-containing proteins. In four of these proteins, Cthe_0258, Cthe_0435, Cthe_0624 and Cthe_0918, there are significant differences in the residues that comprise the two cohesin-binding sites of the type I dockerin domains. In addition, a protein of unknown function (Cthe_0452), containing a C-terminal cohesin highly similar to the equivalent domains present in C. thermocellum-integrating protein (CipA), was also identified. In the present study, the ligand specificities of the newly identified cohesin and dockerin domains are described. The results revealed that Cthe_0452 is located at the C. thermocellum cell surface and thus the protein was renamed as OlpC. The dockerins of Cthe_0258 and Cthe_0435 recognize, preferentially, the OlpC cohesin and thus these enzymes are believed to be predominantly located at the surface of the bacterium. By contrast, the dockerin domains of Cthe_0624 and Cthe_0918 are primarily cellulosomal since they bind preferentially to the cohesins of CipA. OlpC, which is a relatively abundant protein, may also adopt a 'warehouse' function by transiently retaining cellulosomal enzymes at the cell surface before they are assembled on to the multienzyme complex.
authors.affiliation: CIISA-Faculdade de Medicina Veterinária, Pólo Universitário do Alto da Ajuda, Avenida da Universidade Técnica, 1300-477 Lisboa, Portugal.
authors.forename: Benedita A
authors.initials: BA
authors.lastname: Pinheiro
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Gilbert
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Sakka
authors.forename: Kazuo
authors.initials: K
authors.lastname: Sakka
authors.forename: Vânia O
authors.initials: VO
authors.lastname: Fernandes
authors.forename: José A M
authors.initials: JA
authors.lastname: Prates
authors.forename: Victor D
authors.initials: VD
authors.lastname: Alves
authors.forename: David N
authors.initials: DN
authors.lastname: Bolam
authors.forename: Luís M A
authors.initials: LM
authors.lastname: Ferreira
authors.forename: Carlos M G A
authors.initials: CM
authors.lastname: Fontes
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000378:metabolism; D044603:Cellulosomes / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D048013:Acetivibrio thermocellus / Q000235:genetics / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D013816:Thermodynamics; D000097722:Cohesins
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D008565:Membrane Proteins; D000097722:Cohesins; C080369:CipA protein, Clostridium