Structural Evidence for the Evolution of Xyloglucanase Activity from Xyloglucan Endo-Transglycosylases: Biological Implications for Cell Wall Metabolism

• Published in: The Plant cell 2007-06, Vol.19 (6), p.1947-1963
• Main Authors: Baumann, Martin J, Eklöf, Jens M, Michel, Gurvan, Kallas, Åsa M, Teeri, Tuula T, Czjzek, Mirjam, Brumer, Harry III
• Format: Article
• Language: English
• Subjects: Acetates; Biochemistry; Biokemi; Catalysis; Cell Wall - metabolism; Chemistry; Chromatography, Gel; Cloning, Molecular; Crystal structure; crystal-structures; Crystallography; Crystallography, X-Ray; DNA, Complementary - metabolism; endotransglycosylase; Enzymes; Evolution, Molecular; expression analysis; Gene Deletion; germinated nasturtium seeds; Glucans; glycoside hydrolases; Glycoside Hydrolases - chemistry; hybrid aspen; Hydrolysis; kappa-carrageenase; Kemi; Kinetics; Molecular Sequence Data; Mutagenesis; Mutant Proteins - chemistry; Mutant Proteins - metabolism; NATURAL SCIENCES; NATURVETENSKAP; Oligosaccharides; Oligosaccharides - metabolism; Phylogeny; pichia-pastoris; Plant cells; Plant Proteins - chemistry; Plants; Protein Structure, Secondary; Proteins; Recombinant Proteins - metabolism; Seed germination; sequence alignment; Sodium; Static Electricity; Structure-Activity Relationship; Substrate Specificity; Tropaeolum - enzymology; tropaeolum-majus l; Xylans
• ISSN: 1040-4651; 1532-298X; 1532-298X
• DOI: 10.1105/tpc.107.051391

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-ΔYNIIG 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.