The protein encoded by this gene is a type II membrane protein that catalyzes the transfer of sialic acid from CMP-sialic acid to galactose-containing substrates. The encoded protein is normally found in the Golgi but can be proteolytically processed to a soluble form. Correct glycosylation of the encoded protein may be critical to its sialyltransferase activity. This protein, which is a member of glycosyltransferase family 29, can use the same acceptor substrates as does sialyltransferase 4B. Two transcript variants encoding the same protein have been found for this gene. Other transcript variants may exist, but have not been fully characterized yet. [provided by RefSeq, Jul 2008],
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Function:
Catalytic activity:CMP-N-acetylneuraminate + beta-D-galactosyl-1,3-N-acetyl-alpha-D-galactosaminyl-R = CMP + alpha-N-acetylneuraminyl-2,3-beta-D-galactosyl-1,3-N-acetyl-alpha-D-galactosaminyl-R.,Function:It may be responsible for the synthesis of the sequence NeuAc-alpha-2,3-Gal-beta-1,3-GalNAc- found on sugar chains O-linked to Thr or Ser and also as a terminal sequence on certain gangliosides. SIAT4A and SIAT4B sialylate the same acceptor substrates but exhibit different Km values.,online information:GlycoGene database,online information:ST3Gal I,pathway:Protein modification; protein glycosylation.,PTM:The soluble form derives from the membrane form by proteolytic processing.,similarity:Belongs to the glycosyltransferase 29 family.,subcellular location:Membrane-bound form in trans cisternae of Golgi. Secreted into the body fluid.,tissue specificity:Expressed in several tissues. Highest expression in lung, liver, skeletal muscle, kidney, pancreas, spleen and placenta.,
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Cellular Localization:
Golgi apparatus, Golgi stack membrane ; Single-pass type II membrane protein . Golgi apparatus, trans-Golgi network membrane ; Single-pass type II membrane protein . Secreted. Membrane-bound form in medial and trans cisternae of Golgi (PubMed:9182658). Secreted into the body fluid. .
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Tissue Expression:
Expressed in several tissues. Highest expression in lung, liver, skeletal muscle, kidney, pancreas, spleen and placenta.
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Research Areas:
>>Mucin type O-glycan biosynthesis ;
>>Glycosaminoglycan biosynthesis - keratan sulfate ;
>>Glycosphingolipid biosynthesis - globo and isoglobo series ;
>>Glycosphingolipid biosynthesis - ganglio series ;
>>Metabolic pathways