Characterization of alpha 2,3- and alpha 2,6-sialyltransferases from Helicobacter acinonychis

Genome sequence data were used to clone and express two sialyltransferase enzymes of the GT-42 family from Helicobacter acinonychis ATCC 51104, a gastric disease isolate from Cheetahs. The deposited genome sequence for these genes contains a large number of tandem repeat sequences in each of them: HAC1267 (RQKELE) sub(15) and HAC1268 (EEKLLEFKNI) sub(13). We obtained two clones with different numbers of repeat sequences for the HAC1267 gene homolog and a single clone for the HAC1268 gene homolog. Both genes could be expressed in Escherichia coli and sialyltransferase activity was measured using synthetic acceptor substrates containing a variety of terminal sugars. Both enzymes were shown to have a preference for N-acetyllactosamine, and they each made a product with a different linkage to the terminal galactose. HAC1267 is a mono-functional alpha 2,3-sialyltransferase, whereas HAC1268 is a mono-functional alpha 2,6-sialyltransferase and is the first member of GT-42 to show alpha 2,6-sialyltransferase activity.