Ltk leukocyte tyrosine kinase
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
Hematopoietic Cell
B Cell, Pre
95 / 105

Expression
mRNA for human leukocyte tyrosine kinase (Ltk) has been found on hematopoietic cell lines, on a neuroblastoma cell line and in the placenta.  In the mouse, the Ltk message is specific to pre-B cell lines and is highest in the adult but not embryonic brain.  Staining of the mouse brain with polyclonal antiserum was specific for cerebral neurons.  Immunohistochemical staining with peptide mAbs of Hofbauer cells in the human placenta has been reported but in general the level of expression of Ltk is too low to detect with mAbs.

Structure
Ltk is a single chain type 1 glycoprotein.  The extracellular domain does not show similarities with any known protein.  The cytoplasmic tyrosine kinase domain is closely related to that of c-ros.  Alternatively spliced Ltk mRNAs predict the existence of receptors which are soluble or lack a cytoplasmic domain.  The predicted protein sequence of murine Ltk begins at a CTG start codon and does not contain an identifiable signal sequence.  Ltk cDNAs is isolated which predicted a protein devoid of a large extracellular domain probably represent short or aberrant cDNA clones.

MOLECULAR MASS
Cell Type Unreduced Reduced
100 kDa



Ligands
In transfection studies in COS cells, Ltk is associated with PLC-g , PI 3-kinase, GAP and raf-1 and was  dependent on Met544 in a putative ATP binding site.  Analysis of a chimeric receptor revealed that in a ligand-dependent manner, the cytoplasmic domain of Ltk associates with Shc through Tyr862 and Tyr485 which are both contained within a Shc binding motif.

Function
Ltk probably functions as a receptor for an unidentified growth factor.  In an in vitro kinase assay in COS cells, Ltk had kinase activity and was tyrosine phosphorylated.  A chimeric receptor containing the cytoplasmic domain of Ltk was autophosphorylated in response to ligand.

Comments


Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
MouseS00904P08923X07984
Antibodies

Revised June 25, 2008


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