Molecular cloning and expression of human Grap-2, a novel leukocyte-specific SH2- and SH3-containing adaptor-like protein that binds to Gab-1

The SH2- and SH3-containing adaptor molecules serve to recruit cytosolic si gnal-transducing molecules to the activated receptor tyrosine kinases. In t his study, we report the molecular cloning of a novel adaptor-like protein, Grap-2 (Grb-2 related adaptor protein 2), using the multisubstrate docking protein Gab-l as bait in the yeast two-hybrid system. Sequence analysis re vealed that Grap-8 contains a SH3-SH2-SH3 structure that has a high degree of sequence homology to those of the Grb-8 and Grap adaptor molecules. Howe ver, unlike in Grap and Grb-2, the SH2 and the C-terminal SH3 domains of Gr ap-2 are separated by a 120-amino-acid glutamine-rich sequence that shows n o apparent homology to any known molecule or structural motif. The C-termin al SH3 domain of Grap-2 alone is sufficient to bind to Gab-1. Furthermore, Northern blot analysis demonstrated that Grap-8 has two major transcripts o f 1.4 and 4.0 kb that can only be detected in tissues rich in leukocytes an d in two leukemia cell lines. This highly restricted pattern of expression suggests that Grap-2 may participate in leukocyte-specific protein tyrosine kinase signaling, (C) 1998 Academic Press.