IDENTIFICATION OF A NOVEL DIMERIC PHOSPHOPROTEIN (PP29 30) ASSOCIATEDWITH SIGNALING RECEPTORS IN HUMAN T-LYMPHOCYTES AND NATURAL-KILLER-CELLS/

Two-dimensional gel electrophoresis of in vitro phosphorylated protein s coprecipitated by CD2 monoclonal antibody (mAb) from Brij58 lysates of resting human T lymphocytes and natural killer (NK) cells resulted in the identification of a novel 29/30-kD disulfide-linked dimer (pp29 /30). Comparative two-dimensional analysis of CD2, CD3, CD4, CD5, and CD8 immunoprecipitates revealed that pp29/30 associates with these sig naling receptor complexes but not with CD18, CD27, and CD29 in human T lymphocytes. Analysis of CD2 immunoprecipitates prepared from T cell antigen receptor/CD3-modulated T lymphocytes indicated that pp29/30 pr eferentially associates and comodulates with the human T cell antigen receptor (TCR). Since tyrosine phosphorylated pp29/30 selectively inte racts with the Src homology type 2 domains (SHZ) of the protein tyrosi ne kinases p56(lck) and p59(fyn) but not ZAP70 the present data sugges t that pp29/30 represents a novel signaling receptor associated phosph oprotein likely involved in the activation of human T lymphocytes and NK cells.