Consequences of two naturally occurring missense mutations in the structure and function of Bruton agammaglobulinemia tyrosine kinase

Abstract

SummaryBruton agammaglobulinemia tyrosine kinase (BTK) is a key protein in the B-cell receptor (BCR) signaling pathway and plays an essential role in the differentiation of B lymphocytes. X-linked agammaglobulinemia (XLA) is a primary humoral immunodeficiency caused by mutations in the gene encoding BTK. Previously, we identified two novel variations, L111P and E605G, in BTK; these are localized within the pleckstrin homology and Src homology 1 domains, respectively. In the present study, we evaluated the potential effects of these variations on the structural conformation and the function of BTK. Using in silico methods, we found that the L111P and E650G variations are not located directly in protein-protein interfaces but close to them. They distorted the native structural conformation of the BTK protein, affecting not only its geometry and stability but also its ability for protein recognition and in consequence its functionality. To confirm the results of the in silico assays, WT BTK, L111P, and E650G variants were expressed in the BTK-deficient DT40 cell line. The mutant proteins exhibited an absence of catalytic activity, aberrant redistribution after BCR-crosslinking, and deficient intracellular calcium mobilization. This work demonstrates that L111 and E605 residues are fundamental for the activation and function of BTK.2012 IUBMB IUBMB Life, 64(4): [346][347][348][349][350][351][352][353] 2012

Bruton's tyrosine kinase—an integral protein of B cell development that also has an essential role in the innate immune system

“…In our experience, mutations in BTK in a cohort of 14 patients resembled very much the data summarized previously; however, we found two novel mutations (L111P and E605G) that affected the function and structure of Btk [22]. In addition, an important proportion (50%) of these cases has a splice site mutation [23].…”

Atypical X-linked agammaglobulinaemia caused by a novel BTK mutation in a selective immunoglobulin M deficiency patient

“…Computer estimations of the function of p.P116L are labelled “disease-causing” according to MutationTaster (http://www.mutationtaster.org), and “probably damaging” (a HumDiv score of 0.998 and a HumVar score of 0.949) according to PolyPhen-2 (http://genetics.bwh.harvard.edu/pph2/). Further analyses, including the expression of BTK in mononuclear cells from the patients and the alteration in the tyrosine 223 phosphorylation in monocytes after activation through Toll-like receptors [20], should provide the degree of functional defect of this mutation.…”

Los linfocitos B y las inmunodeficiencias primarias

“…53 nos llevaron a comprobar la deficiencia en la función de la proteína utilizando un sistema de células B de pollo, knock-out para Btk. 54 El síndrome de hiper-IgM ligado al cromosoma X ha sido objetivo de otro de nuestros proyectos de investigación, aunque el número de casos diagnosticados en la clínica es limitado; al respecto, se ha reportado una serie de seis pacientes con mutaciones en el gen que codifica para CD40L 55 y actualmente se estudian tres pacientes más que probablemente tengan este defecto.…”