TY - JOUR
T1 - Discrete and structurally unique proteins (ta¯pirins) mediate attachment of extremely thermophilic Caldicellulosiruptor species to cellulose
AU - Blumer-Schuette, Sara E.
AU - Alahuhta, Markus
AU - Conway, Jonathan M.
AU - Lee, Laura L.
AU - Zurawski, Jeffrey V.
AU - Giannone, Richard J.
AU - Hettich, Robert L.
AU - Lunin, Vladimir V.
AU - Himmel, Michael E.
AU - Kelly, Robert M.
N1 - Publisher Copyright:
© 2015, American Society for Biochemistry and Molecular Biology Inc. All rights reserved.
PY - 2015/4/24
Y1 - 2015/4/24
N2 - A variety of catalytic and noncatalytic protein domains are deployed by select microorganisms to deconstruct lignocellulose. These extracellular proteins are used to attach to, modify, and hydrolyze the complex polysaccharides present in plant cell walls. Cellulolytic enzymes, often containing carbohydrate-binding modules, are key to this process; however, these enzymes are not solely responsible for attachment. Few mechanisms of attachment have been discovered among bacteria that do not form large polypeptide structures, called cellulosomes, to deconstruct biomass. In this study, bioinformatics and proteomics analyses identified unique, discrete, hypothetical proteins ("ta¯pirins," origin from Ma¯ori: to join), not directly associated with cellulases, that mediate attachment to cellulose by species in the noncellulosomal, extremely thermophilic bacterial genus Caldicellulosiruptor. Two ta¯pirin genes are located directly downstream of a type IV pilus operon in strongly cellulolytic members of the genus, whereas homologs are absent from the weakly cellulolytic Caldicellulosiruptor species. Based on their amino acid sequence, ta¯pirins are specific to these extreme thermophiles. Ta¯pirins are also unusual in that they share no detectable protein domain signatures with known polysaccharide-binding proteins. Adsorption isotherm and trans vivo analyses demonstrated the carbohydrate-binding module-like affinity of the ta¯pirins for cellulose. Crystallization of a cellulose-binding truncation from one ta¯pirin indicated that these proteins form a long β-helix core with a shielded hydrophobic face. Furthermore, they are structurally unique and define a new class of polysaccharide adhesins. Strongly cellulolytic Caldicellulosiruptor species employ ta¯pirins to complement substrate-binding proteins from the ATP-binding cassette transporters and multidomain extracellular and S-layer-associated glycoside hydrolases to process the carbohydrate content of lignocellulose.
AB - A variety of catalytic and noncatalytic protein domains are deployed by select microorganisms to deconstruct lignocellulose. These extracellular proteins are used to attach to, modify, and hydrolyze the complex polysaccharides present in plant cell walls. Cellulolytic enzymes, often containing carbohydrate-binding modules, are key to this process; however, these enzymes are not solely responsible for attachment. Few mechanisms of attachment have been discovered among bacteria that do not form large polypeptide structures, called cellulosomes, to deconstruct biomass. In this study, bioinformatics and proteomics analyses identified unique, discrete, hypothetical proteins ("ta¯pirins," origin from Ma¯ori: to join), not directly associated with cellulases, that mediate attachment to cellulose by species in the noncellulosomal, extremely thermophilic bacterial genus Caldicellulosiruptor. Two ta¯pirin genes are located directly downstream of a type IV pilus operon in strongly cellulolytic members of the genus, whereas homologs are absent from the weakly cellulolytic Caldicellulosiruptor species. Based on their amino acid sequence, ta¯pirins are specific to these extreme thermophiles. Ta¯pirins are also unusual in that they share no detectable protein domain signatures with known polysaccharide-binding proteins. Adsorption isotherm and trans vivo analyses demonstrated the carbohydrate-binding module-like affinity of the ta¯pirins for cellulose. Crystallization of a cellulose-binding truncation from one ta¯pirin indicated that these proteins form a long β-helix core with a shielded hydrophobic face. Furthermore, they are structurally unique and define a new class of polysaccharide adhesins. Strongly cellulolytic Caldicellulosiruptor species employ ta¯pirins to complement substrate-binding proteins from the ATP-binding cassette transporters and multidomain extracellular and S-layer-associated glycoside hydrolases to process the carbohydrate content of lignocellulose.
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U2 - 10.1074/jbc.M115.641480
DO - 10.1074/jbc.M115.641480
M3 - Article
C2 - 25720489
AN - SCOPUS:84928390955
SN - 0021-9258
VL - 290
SP - 10645
EP - 10656
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 17
ER -