Probing the mechanism of a fungal glycosyltransferase essential for cell wall biosynthesis. UDP-chitobiose is not a substrate for chitin synthase |
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Authors: | Chang Robert Yeager Adam R Finney Nathaniel S |
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Institution: | Department of Chemistry and Biochemistry-0358 University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0358, USA. |
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Abstract: | Chitin synthase is responsible for the biosynthesis of chitin, an essential component of the fungal cell wall. There is a long-standing question as to whether "processive" transferases such as chitin synthase operate in the same manner as non-processive transferases. The question arises from analysis of the polysaccharide structure--in chitin, for instance, each sugar residue is rotated approximately 180 degrees relative to the preceding sugar in the chain. This requires that the enzyme account for the alternating "up/down" configuration during biosynthesis. An enzyme with a single active site, analogous to the non-processive transferases--would have to accommodate a distorted glycosidic linkage at every other synthetic step. An alternative proposal is that the enzyme might assemble the disaccharide donor, addressing the "up/down" conformational problem prior to polymer synthesis. We present compelling evidence that this latter hypothesis is incorrect. |
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