A unified framework for understanding LRRK2 regulation with broad therapeutic implications is provided, showing that the ROC GTPase governs switching between autoinhibited and active states: GTP binding promotes activation, whereas GDP binding enforces autoinhibition.
Abstract
Mutations in leucine-rich repeat kinase 2 (LRRK2) are the second most common cause of autosomal-dominant Parkinson's disease (PD), and increased LRRK2 kinase activity is also observed in idiopathic PD, making LRRK2 a major actionable therapeutic target. LRRK2 is a 286-kDa multidomain enzyme containing a Ras-like GTPase (ROC) and a kinase domain. Using cryo-electron microscopy (cryo-EM), biochemical reconstitution, and cell-based assays, we show that the ROC GTPase governs switching between autoinhibited and active states: GTP binding promotes activation, whereas GDP binding enforces autoinhibition. Two common PD-linked mutations, G2019S and R1441C/G/H, activate LRRK2 through distinct structural mechanisms, revealing genotype-specific routes to dysregulation. These findings provide a unified framework for understanding LRRK2 regulation with broad therapeutic implications. Stabilizing the guanosine diphosphate (GDP)-bound state may inhibit LRRK2 by maintaining autoinhibition, whereas promoting the GTP-bound state could be advantageous in specific cellular contexts, such as the lung, where increased LRRK2 kinase activity may play protective or regulatory roles.
Structural, biochemical, and cellular evidence is integrated to advance a unifying hypothesis that PD-associated LRRK2 dysfunction arises from maladaptive stabilization of specific conformational and spatial states within a membrane-responsive signalling network, leading to persistent misregulation of Rab-dependent trafficking and organelle homeostasis.
Oscar Arias-Carrión, Magdalena Guerra-Crespo, Daniel Ortuño-Sahagún et al.· International Journal of Mol...· 0 citations
Protein phosphatase 2A containing the B56δ regulatory subunit (PP2A-B56δ) is a critical signaling enzyme whose dysregulation is associated with cancer, neurodegenerative disorders, and Jordan’s syndrome, a severe intellectual disability disorder caused by mutations in B56δ. Unlike other PP2A holoenzymes, PP2A-B56δ is regulated through a unique dual autoinhibition mechanism in which the N- and C-arms occlude the catalytic site while a substrate-mimicking short linear motif (SLiM) blocks the substrate-binding pocket. Although disease-associated mutations have been shown to alter enzyme activity, the molecular mechanism underlying activation of PP2A-B56δ and the effects of pathogenic mutations remain poorly understood. Here, we combined cryo-electron microscopy (cryo-EM), enhanced-sampling molecular dynamics (MD) simulations, Markov state model (MSM) construction, and transition-state analysis using Transition State identification via Dispersion and vAriational principle Regularized neural networks (TS-DAR) to characterize the conformational landscape of the disease variant E198K. Our cryo-EM analysis identified two distinct structures of E198K: an inactive closed-form with the N/C-arms resolved and an active loose-form in which the N/C-arms become highly flexible and could not be fully resolved. These structures therefore established that activation is governed by conformational changes of the N/C-arms but did not reveal the underlying mechanism. Starting from the inactive closed-form, we generated over 1,600 trajectories with an average length of 1,260 ns combined for E198K and wild-type (WT) PP2A-B56δ. TS-DAR identified four metastable states and two major activation pathways connecting inactive and active conformations. We found that activation occurs through progressive loosening of the N/C-arm interface while maintaining the overall holoenzyme architecture, rather than a complete opening of the interface. This mechanism exposes both the catalytic site and substrate-binding pocket. Comparison of E198K and WT revealed that the disease-associated mutation shifts the conformational equilibrium toward active states while leaving the transition-state ensemble largely unchanged. Mechanistically, E198K disrupts a salt-bridge network and weakens interactions between the internal loop and the C-arm that normally stabilize active-site occlusion. The resulting increase in C-arm mobility promotes active-site exposure and explains the elevated catalytic activity of the mutant. Together, these findings establish a previously uncharacterized activation mechanism for PP2A-B56δ and provide an atomic-level explanation for how the pathogenic E198K mutation allosterically promotes holoenzyme activation.
Michael S O'Connor, Cheng-Guo Wu, Yichong Lao et al.· bioRxiv· 0 citations
EIF2α kinase heme-regulated inhibitor (HRI) is a novel target for haematological malignancies with modulators reported to trigger cell death via the HRI-eIF2α-ATF4 pathway. We report a protocol for producing the minimal kinase domain of full-length human HRI, termed ‘HRIKD-ΔKI,’ where the unstructured 140 amino acid (aa) kinase insert (KI) within HRI kinase domain (HRIKD) is replaced with a 2aa glycine/serine (GS) linker. X-ray crystal structures were determined of ‘apo’-HRIKD-ΔKI and of its complex with ATP at 2.1 & 2.5 Å resolution respectively. Both structures display a canonical bi-lobal kinase fold. However, they remain in a non-productive state with a displaced C-helix, disassembled R-spine, and a disordered activation segment hindering the substrate site. Biophysical assays (fluorescence based thermal shift & Synchrotron Radiation Circular Dichroism) demonstrate HRIKD-ΔKI retains its functional ligand-binding conformation. All together, these findings define structural and ligand-binding features of HRI to support ongoing drug discovery efforts in blood cancer.
M. Rajasekaran, Jessica Booth, Damien Crepin et al.· bioRxiv· 0 citations
Phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1), a key regulator of mitophagy, has been linked to the pathogenesis of Parkinson’s disease (PD). PINK1 recruits Parkin, an E3 ubiquitin ligase, triggering mitophagy in response to mitochondrial damage. During mitophagy, the quantity, stability, and activity of PINK1 must be strictly regulated; however, the mechanisms governing these parameters under cellular stress are still unclear. Herein, we determined the structural basis for PINK1 maturation mediated by heat shock protein 90alpha/cell division cycle 37/FK506-binding protein 51 (HSP90α/CDC37/FKBP51) chaperone complex. We identified PINK1-associated proteins using liquid chromatography– tandem mass spectrometry (LC-MS/MS) and determined the structures of the complexes using Cryo-Electron Microscopy (Cryo-EM). Results showed that FKBP51 potentially interacts with a conserved leucine–proline–phenylalanine (LPF) motif on the activation loop of PINK1 and negatively regulates PINK1 functions in mitophagy. A PINK1 mutation located at the FKBP51 recognition site is linked to mitophagy deficiency, which can be partially rescued by specific inhibition of FKBP51. These findings reveal a general mechanism for PINK1 recognition by the HSP90α/CDC37/FKBP51 chaperone complex and suggest a potential approach for upregulating PINK1 activity, which is impaired in PD.
Abstract The LRPPRC/SLIRP complex is a key post-transcriptional regulator of mitochondrial gene expression, stabilizing mitochondrial mRNAs and promoting their polyadenylation and translation. Mutations in LRPPRC cause mitochondrial disorders, including Leigh syndrome French-Canadian type (LSFC), primarily affecting oxidative phosphorylation. Here, we examined the RNA-binding properties of wild-type LRPPRC and three pathogenic variants (A354V, K909del, and R1276_K1300del) using electrophoretic mobility shift assays, acoustic force spectroscopy, and AlphaFold 3 modeling. All three mutations reduced intrinsic RNA binding, with R1276_K1300del showing no detectable interaction in the absence of SLIRP. Remarkably, SLIRP restored RNA binding of this mutant to near wild-type levels, likely through conformational stabilization, as supported by single-molecule and structural analyses. These findings highlight SLIRP’s critical role in modulating LRPPRC function and suggest that enhancing SLIRP activity represents a potential therapeutic strategy for LRPPRC-related mitochondrial disorders.
Louise Lambert, U. Rovšnik, A. Moretton et al.· NAR molecular medicine· 0 citations
This work highlights how distinct inhibitors exploit different conformational states of cKIT and demonstrates the value of integrating structural analyses, biophysical measurements, calculations and molecular simulations to define the mechanism of kinase inhibition.
Irene Cipollone, Carmen Gratteri, C. Talarico et al.· International Journal of Bio...· 0 citations
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