A method for making a population of cells that are highly sensitive to clostridial neurotoxin, the method comprising: (a) contacting recombinant cells that express an indicator protein with clostridial neurotoxin; and (b) following such contact, selecting the cells that exhibit cleavage of the indicator protein. A cell from the population produced using the aforementioned method. An assay for determining the activity of a modified or recombinant neurotoxin comprising contacting such a cell with the modified or recombinant neurotoxin under conditions and for a period of time sufficient to allow the protease domain of a wild-type clostridial neurotoxin to cleave the indicator protein in the cell and determining the presence of product resulting from the cleavage of the indicator protein.

The present invention relates to a biotechnological method for producing a C-glycoside of interest. The invention further relates to the use of a sialylated C-glycoside as a donor in an enzymatic glycosylation reaction. The present invention further relates to the following C- glycosides.