Structural synergy and molecular crosstalk between bacterial helicase loaders and replication initiators.

The loading of oligomeric helicases onto replication origins marks an essential step in replisome assembly. In cells, dedicated AAA+ ATPases regulate loading, however, the mechanism by which these factors recruit and deposit helicases has remained unclear. To better understand this process, we determined the structure of the ATPase region of the bacterial helicase loader DnaC from Aquifex aeolicus to 2.7 A resolution. The structure shows that DnaC is a close paralog of the bacterial replication initiator, DnaA, and unexpectedly shares an ability to form a helical assembly similar to that of ATP-bound DnaA. Complementation and ssDNA-binding assays validate the importance of homomeric DnaC interactions, while pull-down experiments show that the DnaC and DnaA AAA+ domains interact in a nucleotide-dependent manner. These findings implicate DnaC as a molecular adaptor that uses ATP-activated DnaA as a docking site for regulating the recruitment and correct spatial deposition of the DnaB helicase onto origins.

Harnessing type I CRISPR-Cas systems for genome engineering in human cells.

Type I CRISPR-Cas systems are the most abundant adaptive immune systems in bacteria and archaea1,2. Target interference relies on a multi-subunit, RNA-guided complex called Cascade3,4, which recruits a trans-acting helicase-nuclease, Cas3, for target degradation5-7. Type I systems have rarely been used for eukaryotic genome engineering applications owing to the relative difficulty of heterologous expression of the multicomponent Cascade complex. Here, we fuse Cascade to the dimerization-dependent, non-specific FokI nuclease domain8-11 and achieve RNA-guided gene editing in multiple human cell lines with high specificity and efficiencies of up to ~50%. FokI-Cascade can be reconstituted via an optimized two-component expression system encoding the CRISPR-associated (Cas) proteins on a single polycistronic vector and the guide RNA (gRNA) on a separate plasmid. Expression of the full Cascade-Cas3 complex in human cells resulted in targeted deletions of up to ~200 kb in length. Our work demonstrates that highly abundant, previously untapped type I CRISPR-Cas systems can be harnessed for genome engineering applications in eukaryotic cells.

USP30 and parkin homeostatically regulate atypical ubiquitin chains on mitochondria.

Multiple lines of evidence indicate that mitochondrial dysfunction is central to Parkinson's disease. Here we investigate the mechanism by which parkin, an E3 ubiquitin ligase, and USP30, a mitochondrion-localized deubiquitylase, regulate mitophagy. We find that mitochondrial damage stimulates parkin to assemble Lys 6, Lys 11 and Lys 63 chains on mitochondria, and that USP30 is a ubiquitin-specific deubiquitylase with a strong preference for cleaving Lys 6- and Lys 11-linked multimers. Using mass spectrometry, we show that recombinant USP30 preferentially removes these linkage types from intact ubiquitylated mitochondria and counteracts parkin-mediated ubiquitin chain formation in cells. These results, combined with a series of chimaera and localization studies, afford insights into the mechanism by which a balance of ubiquitylation and deubiquitylation regulates mitochondrial homeostasis, and suggest a general mechanism for organelle autophagy.

Structural basis of Nav1.7 inhibition by an isoform-selective small-molecule antagonist.

Voltage-gated sodium (Nav) channels propagate action potentials in excitable cells. Accordingly, Nav channels are therapeutic targets for many cardiovascular and neurological disorders. Selective inhibitors have been challenging to design because the nine mammalian Nav channel isoforms share high sequence identity and remain recalcitrant to high-resolution structural studies. Targeting the human Nav1.7 channel involved in pain perception, we present a protein-engineering strategy that has allowed us to determine crystal structures of a novel receptor site in complex with isoform-selective antagonists. GX-936 and related inhibitors bind to the activated state of voltage-sensor domain IV (VSD4), where their anionic aryl sulfonamide warhead engages the fourth arginine gating charge on the S4 helix. By opposing VSD4 deactivation, these compounds inhibit Nav1.7 through a voltage-sensor trapping mechanism, likely by stabilizing inactivated states of the channel. Residues from the S2 and S3 helices are key determinants of isoform selectivity, and bound phospholipids implicate the membrane as a modulator of channel function and pharmacology. Our results help to elucidate the molecular basis of voltage sensing and establish structural blueprints to design selective Nav channel antagonists.

Symptoms affecting quality of life in women with gynecologic cancer.

OBJECTIVES: To review quality-of-life issues in women diagnosed with gynecologic cancers. DATA SOURCES: Research studies, review articles, and medical and nursing text-books. CONCLUSIONS: Women diagnosed with gynecologic cancers carry a heavy physical and emotional burden because of surgical morbidity, chemotherapy toxicities, loss of fertility, changes in body image, sexual concerns, and altered relationships. IMPLICATIONS FOR NURSING PRACTICE: Health care providers play a key role in the identification and treatment of the complications of cancer therapy. Minimizing the effect of the symptoms of gynecologic cancer may positively impact the patient's quality of life.

Backbone cyclization of a recombinant cystine-knot peptide by engineered Sortase A.

Cyclotides belong to the family of cyclic cystine-knot peptides and have shown promise as scaffolds for protein engineering and pharmacological modulation of cellular protein activity. Cyclotides are characterized by a cystine-knotted topology and a head-to-tail cyclic polypeptide backbone. While they are primarily produced in plants, cyclotides have also been obtained by chemical synthesis. However, there is still a need for methods to generate cyclotides in high yields to near homogeneity. Here, we report a biomimetic approach which utilizes an engineered version of the enzyme Sortase A to catalyze amide backbone cyclization of the recombinant cyclotide MCoTI-II, thereby allowing the efficient production of active homogenous species in high yields. Our results provide proof of concept for using engineered Sortase A to produce cyclic MCoTI-II and should be generally applicable to generating other cyclic cystine-knot peptides.

Structural basis for resistance to diverse classes of NAMPT inhibitors.

Inhibiting NAD biosynthesis by blocking the function of nicotinamide phosphoribosyl transferase (NAMPT) is an attractive therapeutic strategy for targeting tumor metabolism. However, the development of drug resistance commonly limits the efficacy of cancer therapeutics. This study identifies mutations in NAMPT that confer resistance to a novel NAMPT inhibitor, GNE-618, in cell culture and in vivo, thus demonstrating that the cytotoxicity of GNE-618 is on target. We determine the crystal structures of six NAMPT mutants in the apo form and in complex with various inhibitors and use cellular, biochemical and structural data to elucidate two resistance mechanisms. One is the surprising finding of allosteric modulation by mutation of residue Ser165, resulting in unwinding of an α-helix that binds the NAMPT substrate 5-phosphoribosyl-1-pyrophosphate (PRPP). The other mechanism is orthosteric blocking of inhibitor binding by mutations of Gly217. Furthermore, by evaluating a panel of diverse small molecule inhibitors, we unravel inhibitor structure activity relationships on the mutant enzymes. These results provide valuable insights into the design of next generation NAMPT inhibitors that offer improved therapeutic potential by evading certain mechanisms of resistance.

An in vivo human-plasmablast enrichment technique allows rapid identification of therapeutic influenza A antibodies.

Recent advances enabling the cloning of human immunoglobulin G genes have proven effective for discovering monoclonal antibodies with therapeutic potential. However, these antibody-discovery methods are often arduous and identify only a few candidates from numerous antibody-secreting plasma cells or plasmablasts. We describe an in vivo enrichment technique that identifies broadly neutralizing human antibodies with high frequency. For this technique, human peripheral blood mononuclear cells from vaccinated donors are activated and enriched in an antigen-specific manner for the production of numerous antigen-specific plasmablasts. Using this technology, we identified four broadly neutralizing influenza A antibodies by screening only 840 human antibodies. Two of these antibodies neutralize every influenza A human isolate tested and perform better than the current anti-influenza A therapeutic, oseltamivir, in treating severe influenza infection in mice and ferrets. Furthermore, these antibodies elicit robust in vivo synergism when combined with oseltamivir, thus highlighting treatment strategies that could benefit influenza-infected patients.

Development and preclinical characterization of a humanized antibody targeting CXCL12.

PURPOSE: Our goal was to develop a potent humanized antibody against mouse/human CXCL12. This report summarized its in vitro and in vivo activities. EXPERIMENTAL DESIGN: Cell surface binding and cell migration assays were used to select neutralizing hamster antibodies, followed by testing in several animal models. Monoclonal antibody (mAb) 30D8 was selected for humanization based on its in vitro and in vivo activities. RESULTS: 30D8, a hamster antibody against mouse and human CXCL12α, CXCL12ß, and CXCL12γ, was shown to dose-dependently block CXCL12α binding to CXCR4 and CXCR7, and CXCL12α-induced Jurkat cell migration in vitro. Inhibition of primary tumor growth and/or metastasis was observed in several models. 30D8 alone significantly ameliorated arthritis in a mouse collagen-induced arthritis model (CIA). Combination with a TNF-α antagonist was additive. In addition, 30D8 inhibited 50% of laser-induced choroidal neovascularization (CNV) in mice. Humanized 30D8 (hu30D8) showed similar in vitro and in vivo activities as the parental hamster antibody. A crystal structure of the hu30D8 Fab/CXCL12α complex in combination with mutational analysis revealed a "hot spot" around residues Asn(44)/Asn(45) of CXCL12α and part of the RFFESH region required for CXCL12α binding to CXCR4 and CXCR7. Finally, hu30D8 exhibited fast clearance in cynomolgus monkeys but not in rats. CONCLUSION: CXCL12 is an attractive target for treatment of cancer and inflammation-related diseases; hu30D8 is suitable for testing this hypothesis in humans.