Download MendeleyStructure of the PH domain from Bruton's tyrosine kinase in complex with inositol 1,3,4,5-tetrakisphosphate.
Baraldi, E., Carugo, K.D., Hyvonen, M., Surdo, P.L., Riley, A.M., Potter, B.V., O'Brien, R., Ladbury, J.E., Saraste, M.(1999) Structure 7: 449-460
- PubMed: 10196129
- DOI: https://doi.org/10.1016/s0969-2126(99)80057-4
- Primary Citation of Related Structures:
1B55, 1BWN - PubMed Abstract:
The activity of Bruton's tyrosine kinase (Btk) is important for the maturation of B cells. A variety of point mutations in this enzyme result in a severe human immunodeficiency known as X-linked agammaglobulinemia (XLA). Btk contains a pleckstrin-homology (PH) domain that specifically binds phosphatidylinositol 3,4,5-trisphosphate and, hence, responds to signalling via phosphatidylinositol 3-kinase. Point mutations in the PH domain might abolish membrane binding, preventing signalling via Btk. We have determined the crystal structures of the wild-type PH domain and a gain-of-function mutant E41K in complex with D-myo-inositol 1,3,4,5-tetra-kisphosphate (Ins (1,3,4,5)P4). The inositol Ins (1,3,4,5)P4 binds to a site that is similar to the inositol 1,4,5-trisphosphate binding site in the PH domain of phospholipase C-delta. A second Ins (1,3,4,5)P4 molecule is associated with the domain of the E41K mutant, suggesting a mechanism for its constitutive interaction with membrane. The affinities of Ins (1,3,4,5)P4 to the wild type (Kd = 40 nM), and several XLA-causing mutants have been measured using isothermal titration calorimetry. Our data provide an explanation for the specificity and high affinity of the interaction with phosphatidylinositol 3,4,5-trisphosphate and lead to a classification of the XLA mutations that reside in the Btk PH domain. Mis-sense mutations that do not simply destabilize the PH fold either directly affect the interaction with the phosphates of the lipid head group or change electrostatic properties of the lipid-binding site. One point mutation (Q127H) cannot be explained by these facts, suggesting that the PH domain of Btk carries an additional function such as interaction with a Galpha protein.
Organizational Affiliation:
European Molecular Biology Laboratory, Meyerhofstrasse 1, Postfach 102209, D-69012 Heidelberg, Germany.
