ASGSB 1998 Annual Meeting Abstracts

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XYLOGLUCAN ENDOTRANSGLYCOSYLASES OF ARABIDOPSIS. P. Campbell and J. Braam. Dept. of Biochemistry and Cell Biology, Rice Univ., Houston, TX.

Arabidopsis possesses a family of xyloglucan endotransglycosylases (XETs), enzymes that endolytically cleave and religate xyloglucan polymers; xyloglucan is one of the primary structural components of the plant cell wall. Therefore, XET function may affect cell shape and plant morphogenesis during growth and in response to mechanical or environmental stimuli. To gain insight into the biochemical functions of this enzyme family, we produced four of the XETs using a baculovirus/Sf9 insect cell expression system. An analysis of the structural requirements of TCH4 for optimal XET activity revealed the necessity of disulfide bonds and N-linked glycosylation for TCH4 activity. Using site-specific mutagenesis, we demonstrated that the first glutamate residue of the conserved DEIDFEFLG motif (E97) is essential for activity. A change to glutamine at this position resulted in an inactive protein, supporting the hypothesis that, in analogy to Bacillus glucanases, this region may be the active site of XET enzymes.

To identify potential unique roles for specific XETs during plant growth, we have compared the activities of four XETs (TCH4, Meri-5, EXT, and XTR9) under several different conditions, including various temperatures, pH's and substrates. (Supported by NASA Specialized Center for Research and Training grant no. NAGW 5007.)

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