Leucine-rich repeat kinase 2 (LRRK2) is a large, multidomain protein containing two catalytic domains: a Ras of complex proteins (Roc) G-domain and a kinase domain. Mutations associated with familial and sporadic Parkinson's disease (PD) have been identified in both catalytic domains, as well as in several of its multiple putative regulatory domains. Several of these mutations have been linked to increased kinase activity. Despite the role of LRRK2 in the pathogenesis of PD, little is known about its overall architecture and how PD-linked mutations alter its function and enzymatic activities. Here, we have modeled the 3D structure of dimeric, full-length LRRK2 by combining domain-based homology models with multiple experimental constraints provided by chemical cross-linking combined with mass spectrometry, negative-stain EM, and small-angle X-ray scattering. Our model reveals dimeric LRRK2 has a compact overall architecture with a tight, multidomain organization. Close contacts between the N-terminal ankyrin and C-terminal WD40 domains, and their proximity-together with the LRR domain-to the kinase domain suggest an intramolecular mechanism for LRRK2 kinase activity regulation. Overall, our studies provide, to our knowledge, the first structural framework for understanding the role of the different domains of full-length LRRK2 in the pathogenesis of PD.LRRK2 | Parkinson's disease | structural modeling | EM | CL-MS

The undersigned authors note the following: "We wish to bring to your attention an issue regarding our PNAS publication referenced above. Although we cite our earlier PNAS publication (see ref. Figs. 2 and 3 display the UWHBs for Hb β-subunit (pdb.1bz0, chain B) and human cellular prion protein (pdb.1qm0) (12)(13)(14). Within the natural interactive context of the Hb subunit, the UWHBs signal crucial binding regions (24): UWHBs (90, 94), (90, 95) are associated with the β-FG corner involved in the quaternary α1β2 interface; UWHB (5, 9) is adjacent to Glu-6 which in sickle cell anemia mutates to Val-6 and is located at the Val-6-(Phe-85, Leu-88) interface in the deoxyHbS fiber."The following text in the section titled 'Toward a Structural Diagnosis' on page 6449 of our text is similar to the text beginning in the last paragraph on page 2392 in ref. 23:The distribution of proteins according to their average extent of hydrogen bond wrapping and their spatial concentration of structural defects is shown in Fig. 5 (see also ref. 23). The sample of 2,811 PDB proteins is large enough to define a reliable abundance distribution with an inflection point at ρ = 6.20. The integration of the distribution over a ρ-interval gives the fraction of proteins whose ρ lies within that range. Of the 2,811 proteins examined, 2,572 have ρ > 6.20, and none of them is known to yield amyloid aggregation under physiological conditions entailing partial retention of structure. Strikingly, relatively few disease-related amyloidogenic proteins are known in the sparsely populated, underwrapped 3.5 < ρ < 6.20 range, with the cellular prion proteins located at the extreme of the spectrum (3.53 < ρ < 3.72)....The range of H-bond wrapping 3.5 < ρ < 4.6 of 20 sampled PDB membrane proteins has been included in Fig. 5 for comparison. As expected, such proteins do not have the stringent H-bond packing requirements of soluble proteins for their H bonds at the lipid interface. Thus, this comparison becomes suggestive in terms of elucidating the driving factor for aggregation in soluble proteins: Although the UWHB constitutes a structural defect in a soluble protein because of its vulnerability to water attack, it is not a structural defect in a membrane protein. The exposure of the polar amide and carbonyl of the unbound state to a nonpolar phase is thermodynamically unfavorable (22). The virtually identical ρ value for human prion and outer-membrane protein A (Fig. 5) is revealing in this regard.Furthermore, all known amyloidogenic proteins that occur naturally in complexed form have sufficient H-bond wrapping within their respective complexes (ρ value near 6.2). Their amyloidogenic propensity appears only under conditions in which the protein is dissociated from the complex (compare Fig. 5). This finding is corroborated by the following computation. If an intramolecular hydrogen bond is underwrapped within the isolated protein molecule but located at an interface upon complexation, then to determine its extent of wrapping within the complex, we take ...

Mutations in LRRK2 are a common cause of genetic Parkinson’s disease (PD). LRRK2 is a multi-domain Roco protein, harbouring kinase and GTPase activity. In analogy with a bacterial homologue, LRRK2 was proposed to act as a GTPase activated by dimerization (GAD), while recent reports suggest LRRK2 to exist under a monomeric and dimeric form in vivo. It is however unknown how LRRK2 oligomerization is regulated. Here, we show that oligomerization of a homologous bacterial Roco protein depends on the nucleotide load. The protein is mainly dimeric in the nucleotide-free and GDP-bound states, while it forms monomers upon GTP binding, leading to a monomer-dimer cycle during GTP hydrolysis. An analogue of a PD-associated mutation stabilizes the dimer and decreases the GTPase activity. This work thus provides insights into the conformational cycle of Roco proteins and suggests a link between oligomerization and disease-associated mutations in LRRK2.

Ataxin-3, the disease protein in Machado-Joseph disease, is known to be proteolytically modified by various enzymes including two major families of proteases, caspases and calpains. This processing results in the generation of toxic fragments of the polyglutamine-expanded protein. Although various approaches were undertaken to identify cleavage sites within ataxin-3 and to evaluate the impact of fragments on the molecular pathogenesis of Machado-Joseph disease, calpain-mediated cleavage of the disease protein and the localization of cleavage sites remained unclear. Here, we report on the first precise localization of calpain cleavage sites in ataxin-3 and on the characterization of the resulting breakdown products. After confirming the occurrence of calpain-derived fragmentation of ataxin-3 in patient-derived cell lines and post-mortem brain tissue, we combined in silico prediction tools, western blot analysis, mass spectrometry, and peptide overlay assays to identify calpain cleavage sites. We found that ataxin-3 is primarily cleaved at two sites, namely at amino acid positions D208 and S256 and mutating amino acids at both cleavage sites to tryptophan nearly abolished ataxin-3 fragmentation. Furthermore, analysis of calpain cleavage-derived fragments showed distinct aggregation propensities and toxicities of C-terminal polyglutamine-containing breakdown products. Our data elucidate the important role of ataxin-3 proteolysis in the pathogenesis of Machado-Joseph disease and further emphasize the relevance of targeting this disease pathway as a treatment strategy in neurodegenerative disorders.

An ad hoc bioconjugation/fluorescence resonance energy transfer (FRET) assay has been designed to spectroscopically monitor the quaternary state of human thymidylate synthase dimeric protein. The approach enables the chemoselective engineering of allosteric residues while preserving the native protein functions through reversible masking of residues within the catalytic site, and is therefore suitable for activity/oligomerization dual assay screenings. It is applied to tag the two subunits of human thymidylate synthase at cysteines 43 and 43 0 with an excitation energy donor/acceptor pair. The dimer-monomer equilibrium of the enzyme is then characterized through steady-state fluorescence determination of the intersubunit resonance energy transfer efficiency.

Intracellular trafficking depends on the function of Rab GTPases, whose activation is regulated by guanine exchange factors (GEFs). The Rab5 GEF, Rabex5, was previously proposed to be auto-inhibited by its C-terminus. Here, we studied full-length Rabex5 and Rabaptin5 proteins as well as domain deletion Rabex5 mutants using hydrogen deuterium exchange mass spectrometry. We generated a structural model of Rabex5, using chemical cross-linking mass spectrometry and integrative modeling techniques. By correlating structural changes with nucleotide exchange activity for each construct, we uncovered new auto-regulatory roles for the ubiquitin binding domains and the Linker connecting those domains to the catalytic core of Rabex5. We further provide evidence that enhanced dynamics in the catalytic core are linked to catalysis. Our results suggest a more complex auto-regulation mechanism than previously thought and imply that ubiquitin binding serves not only to position Rabex5 but to also control its Rab5 GEF activity through allosteric structural alterations.

Human thymidylate synthase (hTS) was targeted through a virtual screening approach. The most optimal inhibitor identified, 2-{4-hydroxy-2-[(2-hydroxybenzylidene)hydrazono]-2,5-dihydrothiazol-5-yl}-N-(3-trifluoromethylphenyl)acetamide (5), showed a mixed-type inhibition pattern, with a K(i) of 1.3 μM and activity against ovarian cancer cell lines with the same potency as cisplatin. X-ray studies revealed that it binds the inactive enzyme conformation. This study is the first example of a nonpeptidic inhibitor that binds the inactive hTS and exhibits anticancer activity against ovarian cancer cells.

Roco proteins have come into focus after mutations in the gene coding for the human Roco protein Leucine-rich repeat kinase 2 (LRRK2) were discovered to be one of the most common genetic causes of late onset Parkinson's disease. Roco proteins are characterized by a Roc domain responsible for GTP binding and hydrolysis, followed by a COR dimerization device. The regulation and function of this RocCOR domain tandem is still not completely understood. To fully biochemically characterize Roco proteins, we performed a systematic survey of the kinetic properties of several Roco protein family members, including LRRK2. Together, our results show that Roco proteins have a unique G-protein cycle. Our results confirm that Roco proteins have a low nucleotide affinity in the micromolar range and thus do not strictly depend on G-nucleotide exchange factors. Measurement of multiple and single turnover reactions shows that neither Pi nor GDP release are rate-limiting, while this is the case for the GAP-mediated GTPase reaction of some small G-proteins like Ras and for most other high affinity Ras-like proteins, respectively. The KM values of the reactions are in the range of the physiological GTP concentration, suggesting that LRRK2 functioning might be regulated by the cellular GTP level.