LPAP SM-1(mouse), CD45-AP(CD45-associated protein-mouse)
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
B Lymphocyte, Activated
T Lymphocyte, Activated
T Lymphocyte, Resting
B Lymphocyte, Resting
25 / 35

The expression of lymphocyte phosphatase-associated phosphoprotein (LPAP) is restricted to resting and activated B and T lymphocytes and to lymphocyte cell lines.

LPAP is a single chain type 1 glycoprotein.  It is comprised of a short extracellular region, a transmembrane region and a large C-terminal cytoplasmic domain.  The 1st 50 aa of the cytoplasmic region share a sequence similarity to WW domains, which have the potential to be involved in protein interaction.  LPAP is expressed in at least 2 different isoforms, LPAP29 and LPAP32, in resting T cells.  These are replaced by LPAP30 and LPAP31 isoforms in activated T cells.  The 4 isoforms appear to be generated by differential phosphorylation in vivo.  The discrepancy between the molecular weight of the polypeptide backbone and the apparent molecular weight determined by SDS-PAGE does not result from the attachment of phosphate groups as in vitro translated material which has a similar Mr.  The N-terminus has been determined by protein sequencing.

Cell Type Unreduced Reduced
Resting T cells 29 kDa, 32 kDa
Activated T cells 30 kDa, 31 kDa

LPAP associates non-covalently with CD45.  The LPAP-CD45 interaction is mediated by the transmembrane regions of the 2 molecules.  An extracellular ligand has not been identified.

LPAP was characterized as a CD45-associated molecule that was detected following in vitro kinase reaction of CD45 immunoprecipitates.  LPAP may function as an adapter molecule that links CD45 with other proteins, possibly through interactions with the putative WW domain.  LPAP is unlikely to play a major role in linking CD45 to the protein tyrosine kinase Lck, because the LPAP-Lck interaction is weak.


Database accession numbers

Revised June 25, 2008

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