endotransglucosylasehydrolases

Endotransglucosylasehydrolases, commonly referred to in the literature as xyloglucan endotransglucosylase/hydrolases (XTH), are a family of plant cell wall enzymes that regulate the remodeling of xyloglucan, a major hemicellulose in primary cell walls.

They catalyze two related activities: endotransglucosylase (xyloglucan endotransglycosylase, XET) activity, in which a segment of xyloglucan is cleaved and rejoined to another xyloglucan chain, and endohydrolase (xyloglucan endohydrolase, XEH) activity, in which xyloglucan is hydrolyzed without transfer. Through these actions, XTH enzymes can modify the cross-links within the cell wall matrix and influence wall loosening and rearrangement.

XTH enzymes are typically secreted into the apoplast, containing an N-terminal signal peptide and often being glycosylated. They belong to glycoside hydrolase family 16 and possess conserved catalytic residues, including two glutamates essential for catalysis, embedded in motifs characteristic of the GH16 family. The balance of transglycosylase versus hydrolase activity varies among family members and can be influenced by pH, temperature, and substrate context.

Expression of XTH genes is developmentally regulated and responsive to hormones and environmental cues, including auxin, light, and abiotic or biotic stresses. In actively growing tissues, XTH transcripts are frequently upregulated, aligning with roles in cell wall loosening and expansion during growth.

Functional diversity within the XTH family underlies context-specific roles in processes such as leaf and stem growth, fruit ripening, abscission, and wood formation. By modulating xyloglucan linkages, endotransglucosylasehydrolases influence cell wall mechanics and biomass properties, making them targets of interest for crop improvement and bioenergy applications.