Hi Frederik,

Our molecular engineering group in Atlanta 10 years ago was involved in enzyme engineering approach to convert glucosyltransferase into galactosyltransferase. To say in a word – unsuccessfully. Why? This very promising problem is a complicated one. Inasmuch as several structures of natural product GTs with bound glycosyl donor (or at least modeled donor) have emerged, and some details regarding substrate binding and catalysis were revealed (Lairson et al., Annu Rev Biochem. 2008;77:521–55), this information remained insufficient to guide this simple engineering exercises - altering sugar C4 specificity, e.g. converting a glucosyltransferase to a galactosyltransferase (Bolam et al. Proc Natl Acad Sci U S A. 2007;104:5336–41; Offen  et al. EMBO J. 2006;25:1396–405). Therefore, continued efforts to obtain new GT-B structures (including different conformational/ligand-bound states of existing solved structures) remain high priority. The recent elucidation of the crystal structure of the C-GT UrdGT2 (Mittler et al. J Mol Biol. 2007;372:67–76) stands as a notable milestone and may pave the way for engineering the production of novel C-glycosides. Further, structural studies targeted toward multiple GTs from single natural product pathways, which are likely evolutionary related may prove fruitful.

Best wishes,

Ilya

Hi Ilya,

thank you for your swift response. Altering C4 specificity is indeed tricky as your own experience confirms. New structural insights and elucidation of structure will indeed prove to be the key in resolving such seemingly easy protein engineering problem...

Much appreciated!

Frederik

I have never tried that myself, but I know that Dr. Qasba reported to alter the GalT to GlcT (http://pubs.acs.org/doi/abs/10.1021/bi0479454). I think his group published a few more interesting publications than the one I referred to here, but I could not find them anymore. Hope this can help you a bit. 

Best regards

Adiphol