GRB4, or NCK adaptor protein 2, is a human gene encoded by NCK2. It may also be known as: Cytoplasmic protein NCK2; Growth factor receptor-bound protein 4; Nck-2; SH2/SH3 adaptor protein NCK-beta; NCKbeta. The encoded protein has an amino acid length of 380 and a mass of 42.9 kDa. Other isoforms may exist. Homologs of this gene exist in other organisms, including: Mouse, Rat, Zebrafish, Frog, Chicken.