Both proline-rich sequences in the TH region of Bruton's tyrosine kinase stabilize intermolecular interactions with the SH3 domain

The Tee homology (TH) region located N-terminal to the Src homology 3 (SH3) domain of Bruton's tyrosine kinase (Btk) contains two proline-rich SH3-bin ding sequences (PRRs). We have previously demonstrated that the TH region a cts to stabilize intermolecular interactions in N-terminally extended SH3 ( PRR-SH3) fragments. Here, we analyze six PRR-SH3 fragments with different p roline-to-alanine substitutions in the two PRRs. Gel permeation chromatogra phy and nuclear magnetic resonance spectroscopy show that both PRRs can sta bilize self-association. This observation provides an explanation to why th e TH region of Btk makes intermolecular interactions, whereas the correspon ding interaction in the related Itk kinase with only one PRR, is intramolec ular. (C) 2001 Federation of European Biochemical Societies. Published by E lsevier Science B.V. All rights reserved.