|Molecule Type||Antigen Expression||Molecular Weight|
Min / Max
|Non-lineage Restricted Molecule|
Type 1 glycoprotein
B Lymphocyte, Resting
|35 / 50|
|ST6Gal 1 is expressed at low to high levels in the heart, brain, placenta, liver, lung, skeletal muscle, kidney, spleen, thymus, prostate, ovary, small intestine, colon and peripheral blood leukocyte. The liver has the highest level of expression. There is variable expression on the HL-60 promyelocytic leukemia cell line and Burkitt's lymphoma B cell lines. There is high expression in mammary glands during late pregnancy and lactation and low to high expression during activation of resting B lymphocytes. ST6Gal 1 is localized in the trans Golgi and trans Golgi network. An active proteolytically cleaved form of the enzyme is found in body fluids such as colostrum, breast milk, blood, lymph and semen. ST6Gal 1 is a transmembrane protein with a C-terminal catalytic domain residing in the Golgi lumen.|
| MOLECULAR FAMILY NAME: hST6gal 1 -->sialytransferase -->glycosyltransferase.|
ST6Gal 1 names: hST6gal 1 (STgal 1) sialyltransferase 1, b-galactoside a-2,60sialyltransferase (CMP-N-acetylneuraminate b-galactoside a-2,6-sialytransferase) and EC 18.104.22.168 (22.214.171.124).
ST6Gal 1 is a type 1 glycoprotein with a C-terminal catalytic domain residing in the Golgi lumen. It is an enzyme belonging to the sialyltransferase family that transfers sialic acid. ST6Gal 1 is comprised of 406 aa, an 1 aa-9 aa cytoplasmic region, a 10 aa-26 aa signal-anchor region, a 27 aa-96 aa stem region, a 97 aa-403 aa catalytic domain, and an 149 aa and 161 aa N-linked glycosylation sites.
The membrane bound enzyme has a molecular weight of 47 kDa whereas the proteolytic released active enzyme is 37 kDa-43 kDa. The membrane bound enzyme may also form an inactive dimer and can act as a galactose binding lectin. The active monomer contains an intramolecular disulfide bond formed by 2 conserved Cys present in the large and small sialyl motifs.
The hST6Gal 1 gene comprises 7-8 exons of which 5 are coding exons. Multiple transcripts differ only in the 5'-untranslated region. Exon X, Y and Z are absent in the liver but exon Y and Z are present in a number of cells and tissues expressing ST6Gal mRNA. Additional mRNA forms utilizing unique exons for the 5'-untranslated region are documented in the mouse.
There are 2 potential N-linked glycosylation sites which have 149 aa and 161aa and for the rat, the sites have 146 aa and 158 aa. These were shown to be modified and important for activity and trafficking of the soluble rate enzyme but not the membrane-bound rat enzyme. Modification by phosphorylation has also been reported.
| LIGANDS AND MOLECULES ASSOCIATED WITH ST6Gal 1: No information.|
| ST6Gal 1 is localized in trans-Golgi and trans-Golgi network in which it acts to add sialic acid to the oligosaccharide chains of the newly synthesized protein while in transit through Golgi. The dimeric form of this enzyme is inactive and may act as a galactose-specific lectin. The enzyme product Sia6LacNAc is a ligand of CD22, a receptor on the B cell, and is shown to be essential in regulating the B lymphocyte activation and immune function. NeuAc6LacNAc also plays a role in the expression of the biological activity of prolactin/growth hormone family members during rat pregnancy.|
ST6Gal 1 transfers sialic acid from CMP-NeuAc to Galb1, 4GlcNac on N-linked glycoproteins yielding NeuAca2-6 Galb1, 4GlcNAc. In vitro, it can also transfer sialic acid to LacNAc and LacdiNAc. ST6Gal 1 can transfer other forms of sialic acid although Neu5Ac is believed to be the precursor of all other varieties known. The optimal pH for this enzyme is 6.0-6.5.
DISEASE RELEVANCE AND FUNCTION OF ST6Gal 1 IN INTACT ANIMAL
ST6Gal 1 deficient mice showed symptoms of immuno-suppression which were marked with reduced serum IgM levels with attenuated antibody production to T-independent and T-dependent antigens. The absence of the enzyme product did not effect B cell development, however these mice showed impaired B cell proliferation in response to IgM or CD40 cross-linking. The deficiency caused an alteration in phosphotyrosine accumulation following cross-linking of the B lymphocyte antigen receptor.
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF ST6Gal 1
ENZYMES WHICH MODIFY ST6Gal 1: No information.
Database accession numbers
Revised June 25, 2008