Rational design and purification of human Bruton's tyrosine kinase SH3-SH2protein for structure-function studies

Bruton's tyrosine kinase (Btk) is a cytoplasmic protein tyrosine kinase con sisting of N-terminal pleck-strin homology (PH) domain followed by Tec homo logy (TH) domain, Src homology 3 and 2 (SH3 and SH2) domains, and a C-termi nal kinase domain. Mutations in the human BTK gene cause the severe immunod eficiency disease X-linked agammaglobulinemia (XLA). The structural and fun ctional basis of several XLA-causing mutations remains unknown, since only the structures of the PH and SH3 domains of human Btk are currently availab le. In this study, we overexpressed and purified a protein consisting of th e SH3 and SH2 domains of human Btk for biochemical and structural analysis. The purified protein was only partially soluble and had a tendency to dime rize, which made it unsuitable for further studies. To overcome the problem s of low solubility and dimerization, subdomain interactions were engineere d without altering the function of the protein. (C) 2000 Academic Press.