Natural Genetic Variation in Yeast Reveals That NEDD4 Is a Conserved Modifier of Mutant Polyglutamine Aggregation.

A feature common to late onset proteinopathic disorders is an accumulation of toxic protein conformers and aggregates in affected tissues. In the search for potential drug targets, many studies used high-throughput screens to find genes that modify the cytotoxicity of misfolded proteins. A complement to this approach is to focus on strategies that use protein aggregation as a phenotypic readout to identify pathways that control aggregate formation and maintenance. Here we use natural variation between strains of budding yeast to genetically map loci that influence the aggregation of a polyglutamine-containing protein derived from a mutant form of huntingtin, the causative agent in Huntington disease. Linkage analysis of progeny derived from a cross between wild and laboratory yeast strains revealed two polymorphic loci that modify polyglutamine aggregation. One locus contains the gene RFU1 which modifies ubiquitination states of misfolded proteins targeted by the E3-ubiquitin ligase complex Rsp5 Activity of the Rsp5 complex, and the mammalian homolog NEDD4, are critical in maintaining protein homeostasis in response to proteomic stress. Our analysis also showed linkage of the aggregation phenotype to a distinct locus containing a gene encoding the Rsp5-interacting Bul2 protein. Allele-swap experiments validated the impact of both RFU1 and BUL2 on huntingtin aggregation. Furthermore, we found that the nematode Caenorhabditis elegans' ortholog of Rsp5, wwp-1, also negatively regulates polyglutamine aggregation. Knockdown of the NEDD4 in human cells likewise altered polyglutamine aggregation. Taken together, these results implicate conserved processes involving the ubiquitin regulation network that modify protein aggregation and provide novel therapeutic targets for polyglutamine and other protein folding diseases.

Design and Structural Characterization of Potent and Selective Inhibitors of Phosphatidylinositol 4 Kinase IIIß.

Type III phosphatidylinositol 4-kinase (PI4KIIIß) is an essential enzyme in mediating membrane trafficking and is implicated in a variety of pathogenic processes. It is a key host factor mediating replication of RNA viruses. The design of potent and specific inhibitors of this enzyme will be essential to define its cellular roles and may lead to novel antiviral therapeutics. We previously reported the PI4K inhibitor PIK93, and this compound has defined key functions of PI4KIIIß. However, this compound showed high cross reactivity with class I and III PI3Ks. Using structure-based drug design, we have designed novel potent and selective (>1000-fold over class I and class III PI3Ks) PI4KIIIß inhibitors. These compounds showed antiviral activity against hepatitis C virus. The co-crystal structure of PI4KIIIß bound to one of the most potent compounds reveals the molecular basis of specificity. This work will be vital in the design of novel PI4KIIIß inhibitors, which may play significant roles as antiviral therapeutics.

Shaping development of autophagy inhibitors with the structure of the lipid kinase Vps34.

Phosphoinositide 3-kinases (PI3Ks) are lipid kinases with diverse roles in health and disease. The primordial PI3K, Vps34, is present in all eukaryotes and has essential roles in autophagy, membrane trafficking, and cell signaling. We solved the crystal structure of Vps34 at 2.9 angstrom resolution, which revealed a constricted adenine-binding pocket, suggesting the reason that specific inhibitors of this class of PI3K have proven elusive. Both the phosphoinositide-binding loop and the carboxyl-terminal helix of Vps34 mediate catalysis on membranes and suppress futile adenosine triphosphatase cycles. Vps34 appears to alternate between a closed cytosolic form and an open form on the membrane. Structures of Vps34 complexes with a series of inhibitors reveal the reason that an autophagy inhibitor preferentially inhibits Vps34 and underpin the development of new potent and specific Vps34 inhibitors.

Human carbonyl reductase 1 is an S-nitrosoglutathione reductase.

Human carbonyl reductase 1 (hCBR1) is an NADPH-dependent short chain dehydrogenase/reductase with broad substrate specificity and is thought to be responsible for the in vivo reduction of quinones, prostaglandins, and other carbonyl-containing compounds including xenobiotics. In addition, hCBR1 possesses a glutathione binding site that allows for increased affinity toward GSH-conjugated molecules. It has been suggested that the GSH-binding site is near the active site; however, no structures with GSH or GSH conjugates have been reported. We have solved the x-ray crystal structures of hCBR1 and a substrate mimic in complex with GSH and the catalytically inert GSH conjugate hydroxymethylglutathione (HMGSH). The structures reveal the GSH-binding site and provide insight into the affinity determinants for GSH-conjugated substrates. We further demonstrate that the structural isostere of HMGSH, S-nitrosoglutathione, is an ideal hCBR1 substrate (Km = 30 microm, kcat = 450 min(-1)) with kinetic constants comparable with the best known hCBR1 substrates. Furthermore, we demonstrate that hCBR1 dependent GSNO reduction occurs in A549 lung adenocarcinoma cell lysates and suggest that hCBR1 may be involved in regulation of tissue levels of GSNO.