The SH2 domain of Abl kinases regulates kinase autophosphorylation by controlling activation loop accessibility

Abstract

The activity of protein kinases is regulated by multiple molecular mechanisms, and their disruption is a common driver of oncogenesis. A central and almost universal control element of protein kinase activity is the activation loop that utilizes both conformation and phosphorylation status to determine substrate access. In this study, we use recombinant Abl tyrosine kinases and conformation-specific kinase inhibitors to quantitatively analyse structural changes that occur after Abl activation. Allosteric SH2-kinase domain interactions were previously shown to be essential for the leukemogenesis caused by the Bcr-Abl oncoprotein. We find that these allosteric interactions switch the Abl activation loop from a closed to a fully open conformation. This enables the trans-autophosphorylation of the activation loop and requires prior phosphorylation of the SH2-kinase linker. Disruption of the SH2-kinase interaction abolishes activation loop phosphorylation. Our analysis provides a molecular mechanism for the SH2 domain-dependent activation of Abl that may also regulate other tyrosine kinases.

Crystal structure of an SH2–kinase construct of c-Abl and effect of the SH2 domain on kinase activity

“…It has also been hypothesized that the formation of the SH2-N-lobe interface may stimulate autophosphorylation on Tyr245 in the SH2 kinase linker, thereby prolonging the activated state [9]. This idea is consistent with recent data demonstrating that the SH2-N-lobe interface impacts strongly autophosphorylation in the SH2-kinase linker and in the activation loop [11,33]. Furthermore, binding partners, as identified in extensive proteomic analyses [34], may modulate Abl activity in the cell.…”

Switch-like activation of Bruton’s tyrosine kinase by membrane-mediated dimerization

“…Indeed, the adventitious dimerization of tyrosine kinases leads to improper activation and cancer, as exemplified by the BCR-Abl fusion protein . The ability of non-receptor tyrosines kinases such as Src and Abl to activate through dimerization and trans-autophosphorylation is well established, but the natural mechanisms that promote dimerization are still not well understood (Lamontanara et al, 2014;Xu et al, 2015). In this regard, the unexpected discovery that Btk can be activated in solution by the binding of IP 6 to the PH-TH module in a way that is consistent with the crystallographically observed Saraste dimer was intriguing, but there was no direct evidence that dimerization was in fact responsible for the observed activation (Wang et al, 2015).…”

Molecular Dynamics Simulations and Structural Network Analysis of c-Abl and c-Src Kinase Core Proteins: Capturing Allosteric Mechanisms and Communication Pathways from Residue Centrality

“…This results in a more rigid inactive conformation of c-Abl KD in the autoinhibitory complex which may be more preferable by Imatinib as compared to c-Src conformation.In a maximally activated "top-hat" conformation of the c-Abl core (Figure 3B), the regulatory complex undergoes a dramatic reshuffling, with the SH2 domain being completely reoriented and migrated to the top of the KD21,22 . This rearrangement releases the autoinhibitory constraints by removing the SH2-SH3 lock, and also allosterically enhances the kinase activity through SH2 binding with the N-terminal lobe of the catalytic core43,44 . A similar domain rearrangement has been observed in regulatory complexes of Fes24 and Btk kinases98 in in which the SH2 domain acts as an allosteric modulator of the kinase activity.…”