Is it possible that a single glycosyltransferase can attach sugar in alpha-linkage and beta-linkage over same compound? For example; beta-linkage glucoside with D-glucose but alpha-linkage glucoside with 2-deoxy D-glucose. I would appreciate the expertise answers with reference.
I would start with looking for the answer here:
Lairson et al (2008) Glycosyltransferases: structures, functions, and mechanisms. Annu Rev Biochem 77: 521-525.
http://www.ncbi.nlm.nih.gov/pubmed?cmd=search&term=18518825
http://www.biotech.uni.wroc.pl/wp-content/uploads/2013/07/annurev.biochGlycosylTransferase.76.061005.pdf
". . . glycosyltransferases catalyze glycosyl group transfer with either inversion or retention of the anomeric stereochemistry with respect to the donor sugar . . ."
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Can one glycosyltransferase employ multiple mechanisms with different substrates? The substrate needs to be oriented properly with respect to the catalytic group (Asp, Glu or His; depending on the type of the glycosyltransferase). Thus, in order for one glycosyltransferase to form alpha linkage with one substrate and beta linkage with another substrate, one of these two things must happen: (a) the two substrates are flipped relative to each other, yet allow for the reaction to occur, or (b) the reactions with the two substrates happen via different mechanisms involving different catalytic residues.
If you have some X-ray crystal structures of your glycosyltransferase and if there is some experimental evidence for the reaction mechanism, you can model the two substrates into the active site (if the crystal structures do not have them) and see if any of the two scenarios is plausible.
Thank you Martin Klvana for your answer including the reference. I will go through the reference materials that you have provided. I would like to know if a single glycosyltransferase that you know so far has inversion and retention properties for a single substrate. I would appreciate more if you know and could provide any research articles as a reference.
Prakash: I am not involved in the glycosyltransferase research field, but if I understand it correctly, different mechanisms of glycosyltransferase reaction would require either different catalytic residues and/or different relative orientation of the substrate with respect to the catalytic residue. I would start with exploring the crystal structures of glycosyltransferases for which the reaction mechanism is known --- what are the structural features that determine the reaction mechanism? Are there any glycosyltransferases that harbor the necessary structural features to catalyze the reaction via alternative mechanisms?
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Is there any crystal structure available for the glycosyltransferase of your interest?
Has anybody proposed the reaction mechanism for your glycosyltransferase?
Are all structural features necessary for the alternative reaction mechanisms present in the active site of your glycosyltransferase?
Assuming alternative products are formed from one substrate, what determines which of the two reactions (with a single substrate) occur each particular instance?
Is there a co-substrate or a modulator involved in any of the possible reaction mechanisms?
Are there any experimental data available that support the formation of different products?
Which amino acid residues are directly involved in the reaction (e.g., based on mutagenesis and kinetics experiments)?
Does the mutation of the assumed key catalytic residue(s) abolish the reaction completely?
Thank you Martin Klvana for your comments over the query. The crystal structure of the glycosyltrasnsferase of my interest is yet to elucidate and its reaction mechanism has been so far predicted I would say. I do not have further experimental data forming different linkage products to support my question. I have an analytical (NMR) data to support the structures formed using this enzyme but how would I support with evidence and references based on the reaction mechanism is a Dilemma.
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