Molecular characterization of pig alpha2,3-Gal-beta1,3-GalNAc-alpha2,6-sialyltransferase (pST6GalNAc IV) gene specific for Neu5Acalpha2-3Galbeta1-3GalNAc trisaccharide structure.

Sialic acids of glycoconjugates play crucial roles in various biological processes, such as cell-cell communication and cell-substrate interaction. A sisalyltransferase, ST6GalNAc IV (Neu5Ac-alpha2,3-Gal-beta1,3-GalNAc-alpha2,6-sialyltransferase), catalyzes the formation of alpha2-6-linkages onto GalNAc residues of O-glycosidically linked Ser/Thr of proteins. In this study, we cloned the pig ST6GalNAc IV (pST6GalNAc IV) and investigated its functional characterization. pST6GalNAc IV cDNA has been isolated from pig liver tissues and it contains an entire open reading frame (ORF, 906 bp) coding for 302 amino acid residues. Entire ORF of pST6GalNAc IV containing sialylmotif 'L'-(Large), 'S'-(Small) and '-VS' (Very small) has a high degree of sequence similarity with Homo sapiens (90%), Pan troglodytes (91%) and Mus musculus (87%). Expression of pST6GalNAc IV mRNA in various pig tissues was identified by reverse transcription polymerase chain reaction (RT-PCR) analysis. pST6GalNAc IV mRNA was highly expressed in tongue, muscle and heart, whereas it was not expressed in pancreas. For functional characterization of pST6GalNAc IV gene in pig kidney PK15 cells, we have also established pST6GalNAc IV-transfected PK15 cells, which are stably expressing the pST6GalNAc IV gene. The glycosylation pattern of pST6GalNAc IV-transfected PK15 cells was detected by flow cytometry and immunofluorescence analysis with Maackia amurensis agglutinin (MAA), Maackia amurensis hemagglutinin (MAL II), Sambucus nigra agglutinin (SNA) and peanut agglutinin (PNA) lectins. The specific carbohydrate structures of Neu5Acalpha2-3Galbeta1-3(Neu5Acalpha2-6)GalNAc tetrasaccharide or Neu5Acalpha2-6GalNAc disaccharide recognized by MAL-II and SNA were revealed to be newly synthesized by pST6GalNAc IV. From the results, it was suggested that the pig pST6GalNAc IV gene is capable of synthesizing Neu5Acalpha2-3Galbeta1-3(Neu5Acalpha2-6)GalNAc tetrasaccharide structures on O-glycoproteins.