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In vitro activities of four xyloglucan endotransglycosylases from Arabidopsis
Author(s) -
Campbell Paul,
Braam Janet
Publication year - 1999
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1999.00459.x
Subject(s) - xyloglucan , arabidopsis , biochemistry , arabidopsis thaliana , oligosaccharide , glycan , enzyme , cell wall , chemistry , biology , gene , glycoprotein , mutant
Summary Xyloglucan endotransglycosylases (XETs) are encoded by a gene family in Arabidopsis thaliana. These enzymes modify a major structural component of the plant cell wall, xyloglucan, and therefore may influence plant growth and development. We have produced four Arabidopsis XETs (TCH4, Meri‐5, EXGT and XTR9) using the baculovirus/insect cell system and compared their biochemical activities. TCH4, as previously demon‐ strated, and the other three proteins are capable of carrying out transglycosylation of xyloglucans. The K m for XLLGol acceptor oligosaccharide is in the range of 20–40 μ m for all the XETs except XTR9, which has a K m of 5 μ m and is significantly inhibited by high levels of XLLGol. All four enzymes are most active between pH 6.0 and 6.5. TCH4 and XTR9 have temperature optima of 18°C, whereas Meri‐5 and EXGT are most active at 28 and 37°C, respectively. Although the activity levels of three of the XETs are not influenced by the presence of fucose on the xyloglucan polymer, XTR9 has a clear preference for non‐fucosylated xyloglucan polymer. The four XETs show a marked preference for XLLGol over either XXFGol or XXXGol as acceptor oligosaccharide. All four XETs are glycosylated; however, only the activities of TCH4 and Meri‐5 are affected by the removal of the N‐glycan with PNGase F. These four enzymes most likely function solely as transglycosylases because xyloglucan endoglucanase activity was not apparent. Subtle differences in biochemical activities may influence the physiological functions of the distinct XETs in vivo.