SH3 Domain Binding Protein 5 (SH3BP5)

Bruton tyrosine kinase (BTK) is a cytoplasmic tyrosine kinase crucial for the maturation of B-lineage cells. BTK deficiency is involved in the pathogenesis of X-linked immunodeficiency.

SH3BP5 encodes a deduced 425-amino acid protein. Northern blot analysis revealed wide expression of a 3.0-kb transcript, with especially prominent expression in testis and ovary. Immunoblot analysis showed that SH3BP5 is expressed as a 70-kD protein. Immunoprecipitation analysis suggested that SH3BP5 interacts with BTK in cells. Mutational and immunoblot analyses showed that amino acids 163 to 193 of SH3BP5 bind most strongly to the SH3 domain of BTK and not with the SH3 domains of a number of other cytoplasmic tyrosine kinases.