SH2 domain

The SH2 (Src Homology 2) domain is a structurally conserved protein domain contained within the Src oncoprotein and in many other intracellular signal-transducing proteins. SH2 domains bind to phosphorylated tyrosine residues on other proteins, modifying the function or activity of the SH2-containing protein. The SH2 domain may be considered the prototypical modular protein-protein interaction domain, allowing the transmission of signals controlling a variety of cellular functions. SH2 domains are especially common in adaptor proteins that aid in the signal transduction of receptor tyrosine kinase pathways. Structure and interactions SH2 domains contain about 100 amino acid residues and exhibit a central antiparallel β-sheet centered between two α-helices. Binding to phosphotyrosine-containing peptides involves a strictly-conserved Arg residue that pairs with the negatively-charged phosphate on the phosphotyrosine, and a surrounding pocket that recognizes flanking sequenc

Allosteric regulation and targeting of Bruton's tyrosine kinase (Btk) in B-cell lymphoma

Daniel Pereira Duarte

Bruton's tyrosine kinase (Btk) is a key component of BCR signaling required for B-cell maturation and activation. Loss-of-function mutations throughout the Btk protein cause human X-linked agammaglobulinemia (XLA), a heritable genetic disorder characterized by the absence of mature B-cells and lack of adaptive immune response. In contrast, Btk signaling sustains the growth of several B-cell neoplasms, which may be treated with small-molecule tyrosine kinase inhibitors (TKIs) targeting the ATP-site of the kinase. No alternative targeted therapy is available for patients who acquire resistance to current Btk inhibitors. Whereas a number of intramolecular interactions amongst the PH, SH3, SH2, and kinase domain (KD) are well resolved and stabilize a compact autoinhibited conformation, the molecular mechanisms governing Btk activation are not fully understood. Using a combination of in silico, structural, cellular, and molecular approaches, we discovered an allosteric interface between the SH2 and the N-lobe of the KD that is critical for kinase activation in vitro and cells. In contrast to the low Btk activity of the KD alone, the presence of the SH2 domain is sufficient to increase Btk phosphorylation at Y551 and multiple other sites. This provides the structural mechanism by which a subset of XLA mutations mapped to the SH2 domain near the interface region strongly perturbs Btk activation, even though the SH2 canonical function is preserved. Furthermore, we demonstrated that the active Btk SH2-kinase adopts an elongated conformation with a dynamic contact interface structurally distinct than to the ones observed for other tyrosine kinases, such as Abl, Fes, and Csk. As allosteric interactions provide unique targeting opportunities far from the ATP-site, we developed an engineered repebody protein binding to the human Btk SH2 domain. The crystal structure of the SH2-repebody complex combined with other structural approaches demonstrated that the repebody disrupts the SH2-kinase interaction. The repebody prevented activation of wild-type and TKI-resistant Btk in vitro and cells seen by a significant decrease in Btk phosphorylation. In parallel, sole allosteric targeting inhibited Btk-dependent signaling and reduced proliferation of malignant B-cells dependent on the BCR signaling. Therefore, the SH2-kinase interface is critical for Btk activation and is the first targetable site able to trigger allosteric inhibition. As Btk targeted therapy has a great impact on several conditions, including B-cell malignancies and autoimmune diseases, this study provides a rationale to support the development of alternative Btk inhibitors. This approach for targeted inhibition could particularly benefit patients with current therapy-resistant Btk variants.

EPFL2020

HRD Motif as the Central Hub of the Signaling Network for Activation Loop Autophosphorylation in Abl Kinase

Oliver Hantschel, Grégory La Sala

A number of structural factors modulate the activity of Abelson (Abl) tyrosine kinase, whose deregulation is often related to oncogenic processes. First, only the open conformation of the Abl kinase domain's activation loop (A-loop) favors ATP binding to the catalytic cleft. In this regard, the trans-autophosphorylation of the Y412 residue, which is located along the A-loop, favors the stability of the open conformation, in turn enhancing Abl activity. Another key factor for full Abl activity is the formation of active conformations of the catalytic DFG motif in the Abl kinase domain. Furthermore, binding of the SH2 domain to the N-lobe of the Abl kinase was recently demonstrated to have a long-range allosteric effect on the stabilization of the A-loop open state. Intriguingly, these distinct structural factors imply a complex signal transmission network for controlling the A-loop's flexibility and conformational preference for optimal Abl function. However, the exact dynamical features of this signal transmission network structure remain unclear. Here, we report on microsecond-long molecular dynamics coupled with enhanced sampling simulations of multiple Abl model systems, in the presence or absence of the SH2 domain and with the DFG motif flipped in two ways (in or out conformation). Through comparative analysis, our simulations augment the interpretation of the existing Abl experimental data, revealing a dynamical network of interactions that interconnect SH2 domain binding with A-loop plasticity and Y412 autophosphorylation in Abl. This signaling network engages the DFG motif and, importantly, other conserved structural elements of the kinase domain, namely, the EPK-ELK H-bond network and the HRD motif. Our results show that the signal propagation for modulating the A-loop spatial localization is highly dependent on the HRD motif conformation, which thus acts as the central hub of this (allosteric) signaling network controlling Abl activation and function.

Amer Chemical Soc2016

Allosteric regulation and targeting of Bruton's tyrosine kinase (Btk) in B-cell lymphoma

Daniel Pereira Duarte

EPFL2020

HRD Motif as the Central Hub of the Signaling Network for Activation Loop Autophosphorylation in Abl Kinase

Oliver Hantschel, Grégory La Sala

Amer Chemical Soc2016

Allosteric regulation and targeting of Bruton's tyrosine kinase (Btk) in B-cell lymphoma

Optogenetic EphB4 receptors clustering with PDZ or SH2 binding domains and chemical clustering with synthetic peptides bioconjugated to Hyaluronic acid

HRD Motif as the Central Hub of the Signaling Network for Activation Loop Autophosphorylation in Abl Kinase

Allosteric regulation and targeting of Bruton's tyrosine kinase (Btk) in B-cell lymphoma

Optogenetic EphB4 receptors clustering with PDZ or SH2 binding domains and chemical clustering with synthetic peptides bioconjugated to Hyaluronic acid

HRD Motif as the Central Hub of the Signaling Network for Activation Loop Autophosphorylation in Abl Kinase