CD328 Siglec7 (sialic acid binding Ig-like lectin 7), SIGLEC-7,  AIRM1, p75, CDw328
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
NK Cell
Leukocyte
Peripheral blood
Liver
Lung
Spleen
Placenta
51 / 51

Expression
CD328 is expressed on resting and activated NK cells, but is expressed at lower levels on granulocytes, monocytes and α/β T cells as well as a small population of CD8+ memory T cells.  High expression is found in the placenta, liver, lung, spleen, and peripheral blood leukocytes.

Structure
MOLECULAR FAMILY NAME: Belongs to the immunoglobulin gene family.

CD328 is a single-pass type-1 449 aa lectin glycoprotein.  It contains an 18 aa signal sequence, a 335 aa extracellular domain which contains a N-terminal Ig-like V-type domain, 2 Ig-like C2-type domains and 8 potential N-linked glycosylation sites, a 23 aa transmembrane domain and a 91 aa intracellular cytoplasmic domain which contains an immunoreceptor tyrosine-based inhibitory motif (ITIM) and a signaling lymphocyte activating molecule (SLAM)-like motif that acts as a docking site for SLAM-associated protein (SAP).  The ITIM motif is involved in modulation of cellular responses.   CD328 belongs to the Ig superfamily which characteristically binds sialic acids at the cell surface.  

MOLECULAR MASS

POST-TRANSCRIPTIONAL MODIFICATION

Alternative splicing yields 4 different isoforms.

POST-TRANSLATIONAL MODIFICATION

CD328 has 8 potential N-linked glycosylation sites.  The cytoplasmic motif is referred to as the immunoreceptor tyrosine-based inhibitor motif (ITIM).  This motif is involved in the modulation of cellular responses.  The phosphorylated ITIM motif can bind the SH 2 domain of several SH-2-containing phosphatases.


Ligands
LIGANDS AND MOLECULE ASSOCIATED WITH CD328

CD328 binds α2,3- and α2,6-linked sialic acid and also binds disialogangliosides such as disialyl Lewis (a) antigen.

Function
CD328 functions as a novel inhibitory receptor.  It is involved in sialic acid dependent adhesion and may inhibit regulation of T cell and NK cell activation and hemopoiesis.  This putative adhesion molecule mediates sialic-acid dependent binding to cells.  The sialic acid recognition may be masked by cis interactions with sialic acids on the same surface.  CD328 mediates sialic acid-dependent cell-cell binding and functions as the inhibitory receptor for NK cells.  In the immune response, CD328 may act as an inhibitory receptor upon ligand induced tyrosine phosphorylation of CD328 ITIM leads to recruitment of the cytoplasmic phosphatase SHP-1.  SHP-1 blocks signal transduction through dephosphorylation of signaling molecules.  There is a mediated inhibition of natural killer cell cytotoxicity that may play a role in hemopoiesis.  There is an inhibited differentiation of CD34+ cell precursors towards myelomonocytic cells and proliferation of leukemic myeloid cells in vitro.  CD328 can negatively affect TCR signaling.  Ligand binding by CD328 leads to recruitment of SHP-1 and subsequently reduced phosphorylation of Tyr319 on ZAP-70, which plays a role in the upregulation of gene transcription after TCR stimulation.

BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD328 IN INTACT ANIMAL: No information.

Comments
MOLECULAR INTERACTIONS-
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD328: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD328: No information.

ADDITIONAL INSIGHTS

For further information see Falco, M. et al (1999) J. Exp. Med. 190: 793-802.


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene27036Q9Y286
Antibodies

Revised June 25, 2008


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