1bwn

From Proteopedia

Revision as of 07:34, 3 February 2008

PH DOMAIN AND BTK MOTIF FROM BRUTON'S TYROSINE KINASE MUTANT E41K IN COMPLEX WITH INS(1,3,4,5)P4

Overview

BACKGROUND: 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. RESULTS: 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. CONCLUSIONS: 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.

Disease

Known diseases associated with this structure: Agammaglobulinemia, type 1, X-linked OMIM:[300300], XLA and isolated growth hormone deficiency OMIM:[300300]

About this Structure

1BWN is a Single protein structure of sequence from Homo sapiens with and as ligands. Active as Transferred entry: 2.7.10.1 and 2.7.10.2, with EC number 2.7.1.112 Known structural/functional Sites: and . Full crystallographic information is available from OCA.

Reference

Structure of the PH domain from Bruton's tyrosine kinase in complex with inositol 1,3,4,5-tetrakisphosphate., Baraldi E, Carugo KD, Hyvonen M, Surdo PL, Riley AM, Potter BV, O'Brien R, Ladbury JE, Saraste M, Structure. 1999 Apr 15;7(4):449-60. PMID:10196129

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