title: Structural evidence for the evolution of xyloglucanase activity from xyloglucan endo-transglycosylases: biological implications for cell wall metabolism.
abstract: High-resolution, three-dimensional structures of the archetypal glycoside hydrolase family 16 (GH16) endo-xyloglucanases Tm-NXG1 and Tm-NXG2 from nasturtium (Tropaeolum majus) have been solved by x-ray crystallography. Key structural features that modulate the relative rates of substrate hydrolysis to transglycosylation in the GH16 xyloglucan-active enzymes were identified by structure-function studies of the recombinantly expressed enzymes in comparison with data for the strict xyloglucan endo-transglycosylase Ptt-XET16-34 from hybrid aspen (Populus tremula x Populus tremuloides). Production of the loop deletion variant Tm-NXG1-DeltaYNIIG yielded an enzyme that was structurally similar to Ptt-XET16-34 and had a greatly increased transglycosylation:hydrolysis ratio. Comprehensive bioinformatic analyses of XTH gene products, together with detailed kinetic data, strongly suggest that xyloglucanase activity has evolved as a gain of function in an ancestral GH16 XET to meet specific biological requirements during seed germination, fruit ripening, and rapid wall expansion.
authors.affiliation: School of Biotechnology, Royal Institute of Technology, AlbaNova University Center, Stockholm, Sweden.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Baumann
authors.forename: Jens M
authors.initials: JM
authors.lastname: Eklöf
authors.forename: Gurvan
authors.initials: G
authors.lastname: Michel
authors.forename: Asa M
authors.initials: AM
authors.lastname: Kallas
authors.forename: Tuula T
authors.initials: TT
authors.lastname: Teeri
authors.forename: Mirjam
authors.initials: M
authors.lastname: Czjzek
authors.forename: Harry
authors.initials: H
authors.lastname: Brumer
mesh_terms: D002384:Catalysis; D002473:Cell Wall / Q000378:metabolism*; D002850:Chromatography, Gel; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D018076:DNA, Complementary / Q000378:metabolism; D019143:Evolution, Molecular; D017353:Gene Deletion; D005936:Glucans; D006026:Glycoside Hydrolases / Q000737:chemistry*; D007700:Kinetics; D008969:Molecular Sequence Data; D016296:Mutagenesis; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009844:Oligosaccharides / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry*; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000378:metabolism; D055672:Static Electricity; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D032388:Tropaeolum / Q000201:enzymology*; D014990:Xylans
chemical_list: D018076:DNA, Complementary; D005936:Glucans; D050505:Mutant Proteins; D009844:Oligosaccharides; D010940:Plant Proteins; D011994:Recombinant Proteins; D014990:Xylans; C029353:xyloglucan; D006026:Glycoside Hydrolases; C072818:xyloglucan endo(1-4)-beta-D-glucanase