title: Fine-structural variance of family 3 carbohydrate-binding modules as extracellular biomass-sensing components of Clostridium thermocellum anti-σI factors.
abstract: The anaerobic, thermophilic, cellulosome-producing bacterium Clostridium thermocellum relies on a variety of carbohydrate-active enzymes in order to efficiently break down complex carbohydrates into utilizable simple sugars. The regulation mechanism of the cellulosomal genes was unknown until recently, when genomic analysis revealed a set of putative operons in C. thermocellum that encode σI factors (i.e. alternative σ factors that control specialized regulon activation) and their cognate anti-σI factor (RsgI). These putative anti-σI-factor proteins have modules that are believed to be carbohydrate sensors. Three of these modules were crystallized and their three-dimensional structures were solved. The structures show a high overall degree of sequence and structural similarity to the cellulosomal family 3 carbohydrate-binding modules (CBM3s). The structures of the three carbohydrate sensors (RsgI-CBM3s) and a reference CBM3 are compared in the context of the structural determinants for the specificity of cellulose and complex carbohydrate binding. Fine structural variations among the RsgI-CBM3s appear to result in alternative substrate preferences for each of the sensors.
authors: Department of Molecular Microbiology and Biotechnology, Tel Aviv University, 69978 Tel Aviv, Israel.
authors: Oren
authors: O
authors: Yaniv
authors: Department of Molecular Microbiology and Biotechnology, Tel Aviv University, 69978 Tel Aviv, Israel.
authors: Galit
authors: G
authors: Fichman
authors: Department of Molecular Microbiology and Biotechnology, Tel Aviv University, 69978 Tel Aviv, Israel.
authors: Ilya
authors: I
authors: Borovok
authors: Department of Biotechnology and Food Engineering, Technion - Israel Institute of Technology, Haifa, Israel.
authors: Yuval
authors: Y
authors: Shoham
authors: Department of Biological Chemistry, The Weizmann Institute of Science, 76100 Rehovot, Israel.
authors: Edward A
authors: EA
authors: Bayer
authors: Department of Molecular Microbiology and Biotechnology, Tel Aviv University, 69978 Tel Aviv, Israel.
authors: Raphael
authors: R
authors: Lamed
authors: Department of Chemical Research Support, The Weizmann Institute of Science, 76100 Rehovot, Israel.
authors: Linda J W
authors: LJ
authors: Shimon
authors: Department of Molecular Microbiology and Biotechnology, Tel Aviv University, 69978 Tel Aviv, Israel.
authors: Felix
authors: F
authors: Frolow
mesh_terms: D000595:Amino Acid Sequence; D018533:Biomass; D002482:Cellulose / Q000737:chemistry* / Q000378:metabolism; D044603:Cellulosomes / Q000737:chemistry / Q000378:metabolism; D048013:Acetivibrio thermocellus / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009876:Operon; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D012808:Sigma Factor / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D040681:Structural Homology, Protein; D013379:Substrate Specificity
chemical_list: D011994:Recombinant Proteins; D012097:Repressor Proteins; D012808:Sigma Factor; C063202:sporulation-specific sigma factors; D002482:Cellulose
keywords: Clostridium thermocellum; RsgI-CBM3; anti-σI factors; family 3 carbohydrate-binding modules