CD229 Ly-9 (lymphocyte antigen 9)
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
Thymocyte
T Cell
B Lymphocyte
T Lymphocyte
Lymph Node
Thymus
Spleen
NK Cell
Leukocyte
Peripheral blood
Leukemia cell
120 / 120

Expression
CD229 is expressed by different leukocytes, is involved in the activation of lymphocytes and NK cells.  Expression is predominantly in the lymph nodes, spleen, thymus and peripheral blood leukocytes.  CD229 has the most restricted expression of the SLAM receptors and is restricted to mature T and B lymphocytes and with the highest levels on thymocytes.  Although CD229 expression is negligible in normal cells of myeloid lineage, a significant number of acute myeloblastic leukemias express CD229.  It is not expressed on monocytes, granulocytes, platelets and red blood cells.


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

CD229 is a single-pass type-1 glycoprotein.  It contains a 407 aa extracellular domain which contains 2 Ig-like C2-type and 2 Ig-like V-type domains and 8 potential N-linked glycosylation sites, a transmembrane domain and a 179 aa cytoplasmic domain and contains 16 threonine residues, 17 serine residues, 8 tyrosines and 2 copies of the tyrosine-based motifs which are critical for binding SLAM-associated protein (SAP) in T cells or the EAT-2 protein in B cells.  It is an Ig domain-containing glycoprotein with structural features which place it within the CD2 family, which includes CD48, CD244 (2B4) and CD150.  CD229 differs from the other CD2 family members in having 4 rather than 2 Ig domains.  Domains 1 and 3 are very similar to each other, as are domains 2 and 4, suggesting that CD229 arose from a progenitor with 1 V and 1 C2 domain, such as CD48.  It is possible that CD229 and CD48 arose by gene duplication from a common ancester with a 2nd duplication step leading to the 4 domain structure of CD229.  The mouse CD229 gene contains 10 exons ranging from 54-355 bp.  Each Ig-like domain is encoded by an individual exon.

MOLECULAR MASS
Cell Type Unreduced Reduced
Transfected cells 120 kDa
B cell Daudi 100 kDa, 120 kDa
Some B cell lines 100 kDa

POST-TRANSCRIPTIONAL MODIFICATION

Alternative splicing yields 3 different isoforms.

POST-TRANSLATIONAL MODIFICATION: No information.


Ligands
LIGANDS AND MOLECULES ASSOCIATED WITH CD229

CD229 parcipates in homophilic binding.

Function
The function of CD229 is unclear, however, its homophilic binding and lymphocyte differentiation may contribute to adhesion between T cells and B cells.  The protein has been shown to relocate to the contact area between T and B cells during antigen-dependent immune synapse formation.  MAb-mediated cross-linking of CD229 induces rapid internalization and degration within lysosomes.  This process is further enhanced by coligation of antigen receptors on T and B cells.  Recent studies have indicated CD229 can negatively regulate TCR signaling.  Analysis of the cytoplasmic tail reveals the presence of various motifs identified with those seen in several receptors involved in cell signaling.  The tail contains 2 unique tyrosine motifs with an aa sequence TxYxxV/I which is also found in the cytoplasmic domain of signaling lymphocyte activation molecule CD150/SLAM, CD244 and CD48.  The motif is critical for binding CD150 and CD244 to a protein called SLAM associated protein (SAP) that is mutated in the immunodeficiency X-linked lymphoproliferative syndrome.  It has been proposed that impaired signaling via these receptors may be responsible for this immunodeficiency.  In activated T cells, the SAP protein binds to and regulates signal transduction events initiated through the engagement of SLAM, CD244, CD48 and CD229.  CD229 is the only member of the CD150 family whose trafficking is regulated by it association with m2, a subunit of the clathrin-associated adaptor complex-2 (AP-2) and its rate of internalizing is controlled by Grb2. 

BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD229 IN INTACT ANIMAL: No information.


Comments
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD229: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD229: No information.


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 4063Q9HBG7
MouseA46500Q01965M84412
Antibodies

Revised June 25, 2008


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