Premium
Competing modes of self‐association in the regulatory domains of Bruton's tyrosine kinase: Intramolecular contact versus asymmetric homodimerization
Author(s) -
Laederach Alain,
Cradic Kendall W.,
Brazin Kristine N.,
Zamoon Jamillah,
Fulton D. Bruce,
Huang XinYun,
Andreotti Amy H.
Publication year - 2002
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.26702
Subject(s) - bruton's tyrosine kinase , sh3 domain , dimer , proline , proto oncogene tyrosine protein kinase src , tyrosine , chemistry , tyrosine kinase , stereochemistry , amino acid , intramolecular force , biophysics , biochemistry , crystallography , kinase , signal transduction , biology , organic chemistry
A nuclear magnetic resonance (NMR) investigation of a fragment of the nonreceptor Tec family tyrosine kinase Btk has revealed an intricate set of coupled monomer‐dimer equilibria. The Btk fragment studied contains two consecutive proline‐rich motifs followed by a single Src homology 3 (SH3) domain. We provide evidence for an asymmetric homodimer in which the amino‐terminal proline sequence of one monomer contacts the opposite SH3 binding pocket, whereas the carboxy‐terminal proline sequence of the other monomer is engaged by the second SH3 domain across the dimer interface. We show that the asymmetric homodimer structure is mimicked by a heterodimer formed in an equimolar mixture of complimentary mutants: one carrying mutations in the amino‐terminal proline stretch; the other, in the carboxy‐terminal proline motif. Moreover, a monomeric species characterized by an intramolecular complex between the amino‐terminal proline motif and the SH3 domain predominates at low concentration. Association constants were determined for each of the competing equilibria by NMR titration. The similarity of the determined K a values reveals a delicate balance between the alternative conformational states available to Btk. Thus, changes in the local concentration of Btk itself, or co‐localization with exogenous signaling molecules that have high affinity for either proline sequence or the SH3 domain, can significantly alter species composition and regulate Btk kinase activity.