A novel member of the mouse
CMP-NeuAc: beta-N-acetylgalactosaminide alpha2,6-sialyltransferase (ST6GalNAc) subfamily, designated
ST6GalNAc V, was identified by BLAST analysis of expressed sequence tags. The sequence of the longest
cDNA clone of
ST6GalNAc V encoded a type II
membrane protein with 8
amino acids comprising the cytoplasmic domain, 21
amino acids comprising the transmembrane region, and 306
amino acids comprising the catalytic domain. The predicted amino acid sequence showed homology to the previously cloned
ST6GalNAc III and IV, with common amino acid sequences in sialyl motifs L and S among these three
enzymes. Eleven CAG repeats were found in the stem region. A fusion
protein with
protein A and extracts from L cells transfected with
ST6GalNAc V in a expression vector showed
enzyme activity of alpha2,6-sialyltransferase almost exclusively for
GM1b, but not toward
glycoproteins.
Sialidase treatment and thin layer chromatography immunostaining revealed that the product was
GD1alpha. Northern blotting revealed that three transcripts of the gene were expressed specifically in brain tissues. It is concluded that this
enzyme is involved in the synthesis of
GD1alpha in the nervous tissues, and the CAG repeats may have implications in
neurodegenerative diseases.