title: Biochemical characterization of highly purified leucine-rich repeat kinases 1 and 2 demonstrates formation of homodimers.
abstract: Leucine-rich repeat kinase 1 and 2 (LRRK1 and LRRK2) are large multidomain proteins containing kinase, GTPase and multiple protein-protein interaction domains, but only mutations in LRRK2 are linked to familial Parkinson's disease (PD). Independent studies suggest that LRRK2 exists in the cell as a complex compatible with the size of a dimer. However, whether this complex is truly a homodimer or a heterologous complex formed by monomeric LRRK2 with other proteins has not been definitively proven due to the limitations in obtaining highly pure proteins suitable for structural characterization. Here, we used stable expression of LRRK1 and LRRK2 in HEK293T cell lines to produce recombinant LRRK1 and LRRK2 proteins of greater than 90% purity. Both purified LRRKs are folded, with a predominantly alpha-helical secondary structure and are capable of binding GTP with similar affinity. Furthermore, recombinant LRRK2 exhibits robust autophosphorylation activity, phosphorylation of model peptides in vitro and ATP binding. In contrast, LRRK1 does not display significant autophosphorylation activity and fails to phosphorylate LRRK2 model substrates, although it does bind ATP. Using these biochemically validated proteins, we show that LRRK1 and LRRK2 are capable of forming homodimers as shown by single-particle transmission electron microscopy and immunogold labeling. These LRRK dimers display an elongated conformation with a mean particle size of 145 Å and 175 Å respectively, which is disrupted by addition of 6M guanidinium chloride. Immunogold staining revealed double-labeled particles also in the pathological LRRK2 mutant G2019S and artificial mutants disrupting GTPase and kinase activities, suggesting that point mutations do not hinder the dimeric conformation. Overall, our findings indicate for the first time that purified and active LRRK1 and LRRK2 can form dimers in their full-length conformation.
authors.affiliation: Department of Biology, University of Padova, Padova, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Civiero
authors.forename: Renée
authors.initials: R
authors.lastname: Vancraenenbroeck
authors.forename: Elisa
authors.initials: E
authors.lastname: Belluzzi
authors.forename: Alexandra
authors.initials: A
authors.lastname: Beilina
authors.forename: Evy
authors.initials: E
authors.lastname: Lobbestael
authors.forename: Lauran
authors.initials: L
authors.lastname: Reyniers
authors.forename: Fangye
authors.initials: F
authors.lastname: Gao
authors.forename: Ivan
authors.initials: I
authors.lastname: Micetic
authors.forename: Marc
authors.initials: M
authors.lastname: De Maeyer
authors.forename: Luigi
authors.initials: L
authors.lastname: Bubacco
authors.forename: Veerle
authors.initials: V
authors.lastname: Baekelandt
authors.forename: Mark R
authors.initials: MR
authors.lastname: Cookson
authors.forename: Elisa
authors.initials: E
authors.lastname: Greggio
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Taymans
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D002845:Chromatography / Q000379:methods; D002942:Circular Dichroism; D019281:Dimerization; D057809:HEK293 Cells; D006801:Humans; D007150:Immunohistochemistry; D016086:Lentivirus / Q000235:genetics; D000090263:Leucine-Rich Repeat Proteins; D000071158:Leucine-Rich Repeat Serine-Threonine Protein Kinase-2; D046529:Microscopy, Electron, Transmission / Q000379:methods; D008856:Microscopy, Fluorescence / Q000379:methods; D009154:Mutation; D010766:Phosphorylation; D017354:Point Mutation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D011506:Proteins / Q000737:chemistry*
chemical_list: D000090263:Leucine-Rich Repeat Proteins; D011506:Proteins; D000255:Adenosine Triphosphate; C510751:LRRK1 protein, human; C495280:LRRK2 protein, human; D000071158:Leucine-Rich Repeat Serine-Threonine Protein Kinase-2; D017346:Protein Serine-Threonine Kinases