Mutations in the PTEN-induced kinase 1 (PINK1) are causative of autosomal recessive Parkinson's disease (PD). We have previously reported that PINK1 is activated by mitochondrial depolarisation and phosphorylates serine 65 (Ser65) of the ubiquitin ligase Parkin and ubiquitin to stimulate Parkin E3 ligase activity. Here, we have employed quantitative phosphoproteomics to search for novel PINK1-dependent phosphorylation targets in HEK (human embryonic kidney) 293 cells stimulated by mitochondrial depolarisation. This led to the identification of 14,213 phosphosites from 4,499 gene products. Whilst most phosphosites were unaffected, we strikingly observed three members of a sub-family of Rab GTPases namely Rab8A, 8B and 13 that are all phosphorylated at the highly conserved residue of serine 111 (Ser111) in response to PINK1 activation. Using phospho-specific antibodies raised against Ser111 of each of the Rabs, we demonstrate that Rab Ser111 phosphorylation occurs specifically in response to PINK1 activation and is abolished in HeLa PINK1 knockout cells and mutant PINK1 PD patient-derived fibroblasts stimulated by mitochondrial depolarisation. We provide evidence that Rab8A GTPase Ser111 phosphorylation is not directly regulated by PINK1 in vitro and demonstrate in cells the time course of Ser111 phosphorylation of Rab8A, 8B and 13 is markedly delayed compared to phosphorylation of Parkin at Ser65. We further show mechanistically that phosphorylation at Ser111 significantly impairs Rab8A activation by its cognate guanine nucleotide exchange factor (GEF), Rabin8 (by using the Ser111Glu phosphorylation mimic). These findings provide the first evidence that PINK1 is able to regulate the phosphorylation of Rab GTPases and indicate that monitoring phosphorylation of Rab8A/8B/13 at Ser111 may represent novel biomarkers of PINK1 activity in vivo. Our findings also suggest that disruption of Rab GTPase-mediated signalling may represent a major mechanism in the neurodegenerative cascade of Parkinson's disease.

Carbonic anhydrases (CAs) are metalloenzymes catalyzing the reversible hydration of carbon dioxide to bicarbonate (hydrogen carbonate) and protons. CAs have been identified in archaea, bacteria and eukaryotes and can be classified into five groups (α, β, γ, δ, ζ) that are unrelated in sequence and structure. The fungal β‐class has only recently attracted attention. In the present study, we investigated the structure and function of the plant‐like β‐CA proteins CAS1 and CAS2 from the filamentous ascomycete Sordaria macrospora. We demonstrated that both proteins can substitute for the Saccharomyces cerevisiae β‐CA Nce103 and exhibit an in vitro CO2 hydration activity (kcat/Km of CAS1: 1.30 × 106 m−1·s−1; CAS2: 1.21 × 106 m−1·s−1). To further investigate the structural properties of CAS1 and CAS2, we determined their crystal structures to a resolution of 2.7 Å and 1.8 Å, respectively. The oligomeric state of both proteins is tetrameric. With the exception of the active site composition, no further major differences have been found. In both enzymes, the Zn2+ ‐ion is tetrahedrally coordinated; in CAS1 by Cys45, His101 and Cys104 and a water molecule and in CAS2 by the side chains of four residues (Cys56, His112, Cys115 and Asp58). Both CAs are only weakly inhibited by anions, making them good candidates for industrial applications. Structured digital abstract CAS1 and  CAS2  bind by  x-ray crystallography ( View interaction) Database Structural data have been deposited in the Protein Data Bank database under accession numbers http://www.rcsb.org/pdb/search/structidSearch.do?structureId=4O1J for CAS1 and http://www.rcsb.org/pdb/search/structidSearch.do?structureId=4O1K for CAS2.

The two β-carbonic anhydrases (CAs, EC 4.2.1.1) recently cloned and purified from the ascomycete fungus Sordaria macrospora, CAS1 and CAS2, were investigated for their inhibition with a panel of 39 aromatic, heterocyclic, and aliphatic sulfonamides and one sulfamate, many of which are clinically used agents. CAS1 was efficiently inhibited by tosylamide, 3-fluorosulfanilamide, and 3-chlorosulfanilamide (KIs in the range of 43.2–79.6 nM), whereas acetazolamide, methazolamide, topiramate, ethoxzolamide, dorzolamide, and brinzolamide were medium potency inhibitors (KIs in the range of 360–445 nM). CAS2 was less sensitive to sulfonamide inhibitors. The best CAS2 inhibitors were 5-amino-1,3,4-thiadiazole-2-sulfonamide (the deacetylated acetazolamide precursor) and 4-hydroxymethyl-benzenesulfonamide, with KIs in the range of 48.1–92.5 nM. Acetazolamide, dorzolamide, ethoxzolamide, topiramate, sulpiride, indisulam, celecoxib, and sulthiame were medium potency CAS2 inhibitors (KIs of 143–857 nM). Many other sulfonamides showed affinities in the high micromolar range or were ineffective as CAS1/2 inhibitors. Small changes in the structure of the inhibitor led to important differences of the activity. As these enzymes may show applications for the removal of anthropically generated polluting gases, finding modulators of their activity may be crucial for designing environmental-friendly CO2 capture processes.

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