Structural analyses of the putative mannosylphosphate transferase, Ktr6p from «Saccharomyces cerevisiae»

Le résumé fourni par la source

The post-translational addition of sugar moieties onto proteins plays an important role in protein folding, secretion, signaling, and is even thought to partake in cell-cell adhesion. In eukaryotes, the biosynthesis of N-glycans begins with the transfer of Glc3Man9GlcNAc2 to the amide group of an asparagine situated in the tripeptide Asn-X-Thr(Ser), of a protein. Subsequent removal of three glucoses and one mannose occurs in the Endoplasmic Reticulum. In yeast, those proteins that require further maturation, e.g. those destined to enter the secretory pathway, are sent to the cis-Golgi. The core, Man8GlcNAc2, is then decorated with additional mannoses and mannose-1-phosphates. The enzyme responsible for the transfer of mannose-1-phosphate in Saccharomyces cerevisiae is Ktr6p. It is a member of the Kre Two Related family of mannosyltransferases: Kre2p. Ktr6p shares 38% sequence identity with Kre2p, suggesting a similar three-dimensional structure. However, greater than 50% of the residues in the Ktr6p putative active site differ from Kre2p, signifying that Ktr6p may have a modified mannosyltransferase function. For these aforementioned reasons, crystallographic studies on this putative mannosylphosphate transferase are pursued. Here, we present the methods employed to obtain the final Ktr6p crystal structure that has been solved, via molecular replacement, to a resolution of 3.11 Å. A detailed discussion analyzing the results obtained ensues.

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