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PubMed · 10972897

Structure-function effects in primary immunodeficiencies.

Abstract

Several immunodeficiency-related genes have been identified and a large number of mutations in these genes. Currently, a genetic defect has been determined in more than 2000 patients. Only recently has it become possible to address structure-function effects of these mutations in the corresponding proteins. The consequences of mutations in structure are discussed for Btk in X-linked agammaglobulinemia (XLA), Jak3 in T-B+ severe combined immunodeficiency (SCID), p47phox and p67phox in autosomal chronic granulomatous disease (CGD) and SH2D1 A in X-linked lymphoproliferatine disease (XLP). The experimental and homology modelling derived structures were used to analyze mechanisms related to these diseases.

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BibTeXRIS

M Korpi, J Väliaho, M Vihinen. 2000. Structure-function effects in primary immunodeficiencies.. https://doi.org/10.1046/j.1365-3083.2000.00799.x

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A conditional form of Bruton's tyrosine kinase is sufficient to activate multiple downstream signaling pathways via PLC Gamma 2 in B cells.

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Identification of phosphorylation sites for Bruton's tyrosine kinase within the transcriptional regulator BAP/TFII-I.

Bruton's tyrosine kinase (Btk), a member of the Tec family of cytosolic kinases, is essential for B cell development and function. BAP/TFII-I, a protein implicated in transcriptional regulation, is associated with Btk in B cells and is transiently phosphorylated on tyrosine following B cell receptor engagement. BAP/TFII-I is a substrate for Btk in vitro and is hyperphosphorylated on tyrosine upon coexpression with Btk in mammalian cells. In an effort to understand the physiologic consequences of BAP/TFII-I tyrosine phosphorylation following B cell receptor stimulation, site-directed mutagenesis and phosphopeptide mapping were used to locate the predominant sites of BAP/TFII-I phosphorylation by Btk in vitro. These residues, Tyr248, Tyr357, and Tyr462, were also found to be the major sites for Btk-dependent phosphorylation of BAP/TFII-I in vivo. Residues Tyr357 and Tyr462 are contained within the loop regions of adjacent helix-loop-helix-like repeats within BAP/TFII-I. Mutation of either Tyr248, Tyr357, or Tyr462 to phenylalanine reduced transcription from a c-fos promoter relative to wild-type BAP/TFII-I in transfected COS-7 cells, consistent with the interpretation that phosphorylation at these sites contributes to transcriptional activation. Phosphorylation of BAP/TFII-I by Btk may link engagement of receptors such as surface immunoglobulin to modulation of gene expression.

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Bruton's tyrosine kinase (Btk) is a nonreceptor tyrosine kinase involved in precursor B (pre-B) cell receptor signaling. Here we demonstrate that Btk-deficient mice have an approximately 50% reduction in the frequency of immunoglobulin (Ig) lambda light chain expression, already at the immature B cell stage in the bone marrow. Conversely, transgenic mice expressing the activated mutant Btk(E41K) showed increased lambda usage. As the kappa/lambda ratio is dependent on (a) the level and kinetics of kappa and lambda locus activation, (b) the life span of pre-B cells, and (c) the extent of receptor editing, we analyzed the role of Btk in these processes. Enforced expression of the Bcl-2 apoptosis inhibitor did not alter the Btk dependence of lambda usage. Crossing 3-83mudelta autoantibody transgenic mice into Btk-deficient mice showed that Btk is not essential for receptor editing. Also, Btk-deficient surface Ig(+) B cells that were generated in vitro in interleukin 7-driven bone marrow cultures manifested reduced lambda usage. An intrinsic defect in lambda locus recombination was further supported by the finding in Btk-deficient mice of reduced lambda usage in the fraction of pre-B cells that express light chains in their cytoplasm. These results implicate Btk in the regulation of the activation of the lambda locus for V(D)J recombination in pre-B cells.

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