Structure and dynamics of a pentameric KCTD5/CUL3/Gßγ E3 ubiquitin ligase complex.

Heterotrimeric G proteins can be regulated by posttranslational modifications, including ubiquitylation. KCTD5, a pentameric substrate receptor protein consisting of an N-terminal BTB domain and a C-terminal domain, engages CUL3 to form the central scaffold of a cullin-RING E3 ligase complex (CRL3KCTD5) that ubiquitylates Gßγ and reduces Gßγ protein levels in cells. The cryo-EM structure of a 5:5:5 KCTD5/CUL3NTD/Gß1γ2 assembly reveals a highly dynamic complex with rotations of over 60° between the KCTD5BTB/CUL3NTD and KCTD5CTD/Gßγ moieties of the structure. CRL3KCTD5 engages the E3 ligase ARIH1 to ubiquitylate Gßγ in an E3-E3 superassembly, and extension of the structure to include full-length CUL3 with RBX1 and an ARIH1~ubiquitin conjugate reveals that some conformational states position the ARIH1~ubiquitin thioester bond to within 10 Å of lysine-23 of Gß and likely represent priming complexes. Most previously described CRL/substrate structures have consisted of monovalent complexes and have involved flexible peptide substrates. The structure of the KCTD5/CUL3NTD/Gßγ complex shows that the oligomerization of a substrate receptor can generate a polyvalent E3 ligase complex and that the internal dynamics of the substrate receptor can position a structured target for ubiquitylation in a CRL3 complex.

Circulating transthyretin and retinol binding protein 4 levels among middle-age V122I TTR carriers in the general population.

BACKGROUND: Hereditary transthyretin cardiac amyloidosis (ATTRv-CA) has a long latency phase before clinical onset, creating a need to identify subclinical disease. We hypothesized circulating transthyretin (TTR) and retinol binding protein 4 (RBP4) levels would be associated with TTR carrier status and correlated with possible evidence of subclinical ATTRv-CA. METHODS: TTR and RBP4 were measured in blood samples from V122I TTR carriers and age-, sex- and race-matched non-carrier controls (1:2 matching) among Dallas Heart Study participants (phases 1 (DHS-1) and 2 (DHS-2)). Multivariable linear regression models determined factors associated with TTR and RBP4. RESULTS: There were 40 V122I TTR carriers in DHS-1 and 54 V122I TTR carriers in DHS-2. In DHS-1 and DHS-2, TTR was lower in V122I TTR carriers (p < .001 for both), and RBP4 in DHS-2 was lower in V122I TTR carriers than non-carriers (p = .002). Among V122I TTR carriers, TTR was negatively correlated with markers of kidney function, and limb lead voltage (p < .05 for both) and TTR and RBP4 were correlated with atrial volume in DHS-2 (p < .05). CONCLUSIONS: V122I TTR carrier status is independently associated with lower TTR and RBP4 in comparison with non-carriers. These findings support the hypothesis that TTR and RBP4 may correlate with evidence of subclinical ATTRv-CA.

Structural Insights into KCTD Protein Assembly and Cullin3 Recognition.

Cullin3 (Cul3)-based ubiquitin E3 ligase complexes catalyze the transfer of ubiquitin from an E2 enzyme to target substrate proteins. In these assemblies, the C-terminal region of Cul3 binds Rbx1/E2-ubiquitin, while the N-terminal region interacts with various BTB (bric-à-brac, tramtrack, broad complex) domain proteins that serve as substrate adaptors. Previous crystal structures of the homodimeric BTB proteins KLHL3, KLHL11 and SPOP in complex with the N-terminal domain of Cul3 revealed the features required for Cul3 recognition in these proteins. A second class of BTB-domain-containing proteins, the KCTD proteins, is also Cul3 substrate adaptors, but these do not share many of the previously identified determinants for Cul3 binding. We report the pentameric crystal structures of the KCTD1 and KCTD9 BTB domains and identify plasticity in the KCTD1 rings. We find that the KCTD proteins 5, 6, 9 and 17 bind to Cul3 with high affinity, while the KCTD proteins 1 and 16 do not have detectable binding. Finally, we confirm the 5:5 assembly of KCTD9/Cul3 complexes by cryo-electron microscopy and provide a molecular rationale for BTB-mediated Cul3 binding specificity in the KCTD family.

The integrated landscape of driver genomic alterations in glioblastoma.

Glioblastoma is one of the most challenging forms of cancer to treat. Here we describe a computational platform that integrates the analysis of copy number variations and somatic mutations and unravels the landscape of in-frame gene fusions in glioblastoma. We found mutations with loss of heterozygosity in LZTR1, encoding an adaptor of CUL3-containing E3 ligase complexes. Mutations and deletions disrupt LZTR1 function, which restrains the self renewal and growth of glioma spheres that retain stem cell features. Loss-of-function mutations in CTNND2 target a neural-specific gene and are associated with the transformation of glioma cells along the very aggressive mesenchymal phenotype. We also report recurrent translocations that fuse the coding sequence of EGFR to several partners, with EGFR-SEPT14 being the most frequent functional gene fusion in human glioblastoma. EGFR-SEPT14 fusions activate STAT3 signaling and confer mitogen independence and sensitivity to EGFR inhibition. These results provide insights into the pathogenesis of glioblastoma and highlight new targets for therapeutic intervention.

Crystal structure of KLHL3 in complex with Cullin3.

KLHL3 is a BTB-BACK-Kelch family protein that serves as a substrate adapter in Cullin3 (Cul3) E3 ubiquitin ligase complexes. KLHL3 is highly expressed in distal nephron tubules where it is involved in the regulation of electrolyte homeostasis and blood pressure. Mutations in KLHL3 have been identified in patients with inherited hypertension disorders, and several of the disease-associated mutations are located in the presumed Cul3 binding region. Here, we report the crystal structure of a complex between the KLHL3 BTB-BACK domain dimer and two copies of an N terminal fragment of Cul3. We use isothermal titration calorimetry to directly demonstrate that several of the disease mutations in the KLHL3 BTB-BACK domains disrupt the association with Cul3. Both the BTB and BACK domains contribute to the Cul3 interaction surface, and an extended model of the dimeric CRL3 complex places the two E2 binding sites in a suprafacial arrangement with respect to the presumed substrate-binding sites.