Activation of an Endoribonuclease by Non-intein Protein Splicing.

The Chlamydomonas reinhardtii chloroplast-localized poly(A)-binding protein RB47 is predicted to contain a non-conserved linker (NCL) sequence flanked by highly conserved N- and C-terminal sequences, based on the corresponding cDNA. RB47 was purified from chloroplasts in association with an endoribonuclease activity; however, protein sequencing failed to detect the NCL. Furthermore, while recombinant RB47 including the NCL did not display endoribonuclease activity in vitro, versions lacking the NCL displayed strong activity. Both full-length and shorter forms of RB47 could be detected in chloroplasts, with conversion to the shorter form occurring in chloroplasts isolated from cells grown in the light. This conversion could be replicated in vitro in chloroplast extracts in a light-dependent manner, where epitope tags and protein sequencing showed that the NCL was excised from a full-length recombinant substrate, together with splicing of the flanking sequences. The requirement for endogenous factors and light differentiates this protein splicing from autocatalytic inteins, and may allow the chloroplast to regulate the activation of RB47 endoribonuclease activity. We speculate that this protein splicing activity arose to post-translationally repair proteins that had been inactivated by deleterious insertions or extensions.

Preventable pediatric intensive care unit admissions over a 13-year period at a level 1 pediatric trauma center.

BACKGROUND: No formal criteria exist to determine the need for admission of injured children to the pediatric intensive care unit. Our objective was to analyze trauma patient admissions to the PICU at a level 1 pediatric trauma center. METHODS: The trauma registry was analyzed between 2002 and 2015. A preventable PICU admission was defined as a child discharged home or transferred out of the PICU within 30h without surgical intervention, blood transfusion, or ventilator support. RESULTS: Of 16,209 children, 19% were admitted to the PICU: mean age 7.3years, median ISS 17, and overall mortality 7%. Per our definition, 36% were preventable PICU admissions of which 83% suffered a head injury. The preventable admissions were younger (6.9 vs. 7.6years, p<0.001) with a lower median ISS (16 vs. 21, p<0.001), shorter median PICU LOS (17 vs. 41h, p<0.001) and shorter median hospital LOS (51 vs. 121h, p<0.001). These admissions resulted in total facility charges of $9,981,454.76 with 54% produced by children with an isolated head injury. CONCLUSIONS: A significant number of children admitted to our PICU were classified as preventable. They carry a substantial economic burden to the health care system with an overutilization of resources. Methods to limit such admissions should be actively pursued.

Molecular insights into the function of RING finger (RNF)-containing proteins hRNF8 and hRNF168 in Ubc13/Mms2-dependent ubiquitylation.

The repair of DNA double strand breaks by homologous recombination relies on the unique topology of the chains formed by Lys-63 ubiquitylation of chromatin to recruit repair factors such as breast cancer 1 (BRCA1) to sites of DNA damage. The human RING finger (RNF) E3 ubiquitin ligases, RNF8 and RNF168, with the E2 ubiquitin-conjugating complex Ubc13/Mms2, perform the majority of Lys-63 ubiquitylation in homologous recombination. Here, we show that RNF8 dimerizes and binds to Ubc13/Mms2, thereby stimulating formation of Lys-63 ubiquitin chains, whereas the related RNF168 RING domain is a monomer and does not catalyze Lys-63 polyubiquitylation. The crystal structure of the RNF8/Ubc13/Mms2 ternary complex reveals the structural basis for the interaction between Ubc13 and the RNF8 RING and that an extended RNF8 coiled-coil is responsible for its dimerization. Mutations that disrupt the RNF8/Ubc13 binding surfaces, or that truncate the RNF8 coiled-coil, reduce RNF8-catalyzed ubiquitylation. These findings support the hypothesis that RNF8 is responsible for the initiation of Lys-63-linked ubiquitylation in the DNA damage response, which is subsequently amplified by RNF168.

Visualizing the drug target landscape.

Generating new therapeutic hypotheses for human disease requires the analysis and interpretation of many different experimental datasets. Assembling a holistic picture of the current landscape of drug discovery activity remains a challenge, however, because of the lack of integration between biological, chemical and clinical resources. Although tools designed to tackle the interpretation of individual data types are abundant, systems that bring together multiple elements to directly enable decision making within drug discovery programmes are rare. In this article, we review the path that led to the development of a knowledge system to tackle this problem within our organization and highlight the influences of existing technologies on its development. Central to our approach is the use of visualization to better convey the overall meaning of an integrated set of data including disease association, druggability, competitor intelligence, genomics and text mining. Organizing such data along lines of therapeutic precedence creates clearly distinct 'zones' of pharmaceutical opportunity, ranging from small-molecule repurposing to biotherapeutic prospects and gene family exploitation. Mapping content in this way also provides a visual alerting mechanism that evaluates new evidence in the context of old, reducing information overload by filtering redundant information. In addition, we argue the need for more tools in this space and highlight the role that data standards, new technologies and increased collaboration might have in achieving this aim.

Exploiting the P-1 pocket of BRCT domains toward a structure guided inhibitor design.

Breast cancer gene 1 carboxy terminus (BRCT) domains are found in a number of proteins that are important for DNA damage response (DDR). The BRCT domains bind phosphorylated proteins and these protein-protein interactions are essential for DDR and DNA repair. High affinity domain specific inhibitors are needed to facilitate the dissection of the protein-protein interactions in the DDR signaling. The BRCT domains of BRCA1 bind phosphorylated protein through a pSXXF consensus recognition motif. We identified a hydrophobic pocket at the P-1 position of the pSXXF binding site. Here we conducted a structure-guided synthesis of peptide analogs with hydrophobic functional groups at the P-1 position. Evaluation of these led to the identification of a peptide mimic 15 with a inhibitory constant (K(i)) of 40 nM for BRCT(BRCA1). Analysis of the TopBP1 and MDC1 BRCT domains suggests a similar approach is viable to design high affinity inhibitors.

Solution properties of murine leukemia virus gag protein: differences from HIV-1 gag.

Immature retrovirus particles are assembled from the multidomain Gag protein. In these particles, the Gag proteins are arranged radially as elongated rods. We have previously characterized the properties of HIV-1 Gag in solution. In the absence of nucleic acid, HIV-1 Gag displays moderately weak interprotein interactions, existing in monomer-dimer equilibrium. Neutron scattering and hydrodynamic studies suggest that the protein is compact, and biochemical studies indicate that the two ends can approach close in three-dimensional space, implying the need for a significant conformational change during assembly. We now describe the properties of the Gag protein of Moloney murine leukemia virus (MLV), a gammaretrovirus. We found that this protein is very different from HIV-1 Gag: it has much weaker protein-protein interaction and is predominantly monomeric in solution. This has allowed us to study the protein by small-angle X-ray scattering and to build a low-resolution molecular envelope for the protein. We found that MLV Gag is extended in solution, with an axial ratio of ∼7, comparable to its dimensions in immature particles. Mutational analysis suggests that runs of prolines in its matrix and p12 domains and the highly charged stretch at the C terminus of its capsid domain all contribute to this extended conformation. These differences between MLV Gag and HIV-1 Gag and their implications for retroviral assembly are discussed.

Comparison of the structures and peptide binding specificities of the BRCT domains of MDC1 and BRCA1.

The tandem BRCT domains of BRCA1 and MDC1 facilitate protein signaling at DNA damage foci through specific interactions with serine-phosphorylated protein partners. The MDC1 BRCT binds pSer-Gln-Glu-Tyr-COO(-) at the C terminus of the histone variant gammaH2AX via direct recognition of the C-terminal carboxylate, while BRCA1 recognizes pSer-X-X-Phe motifs either at C-terminal or internal sites within target proteins. Using fluorescence polarization binding assays, we show that while both BRCTs prefer a free main chain carboxylate at the +3 position, this preference is much more pronounced in MDC1. Crystal structures of BRCA1 and MDC1 bound to tetrapeptide substrates reveal differences in the environment of conserved arginines (Arg1699 in BRCA1 and Arg1933 in MDC1) that determine the relative affinity for peptides with -COO(-) versus -CO-NH(2) termini. A mutation in MDC1 that induces a more BRCA1-like conformation relaxes the binding specificity, allowing the mutant to bind phosphopeptides lacking a -COO(-) terminus.

Visualizing the drug target landscape.

Generating new therapeutic hypotheses for human disease requires the analysis and interpretation of many different experimental datasets. Assembling a holistic picture of the current landscape of drug discovery activity remains a challenge, however, because of the lack of integration between biological, chemical and clinical resources. Although tools designed to tackle the interpretation of individual data types are abundant, systems that bring together multiple elements to directly enable decision making within drug discovery programmes are rare. In this article, we review the path that led to the development of a knowledge system to tackle this problem within our organization and highlight the influences of existing technologies on its development. Central to our approach is the use of visualization to better convey the overall meaning of an integrated set of data including disease association, druggability, competitor intelligence, genomics and text mining. Organizing such data along lines of therapeutic precedence creates clearly distinct 'zones' of pharmaceutical opportunity, ranging from small-molecule repurposing to biotherapeutic prospects and gene family exploitation. Mapping content in this way also provides a visual alerting mechanism that evaluates new evidence in the context of old, reducing information overload by filtering redundant information. In addition, we argue the need for more tools in this space and highlight the role that data standards, new technologies and increased collaboration might have in achieving this aim.

Interactions between HIV-1 Gag molecules in solution: an inositol phosphate-mediated switch.

Retrovirus particle assembly is mediated by the Gag protein. Gag is a multi-domain protein containing discrete domains connected by flexible linkers. When recombinant HIV-1 Gag protein (lacking myristate at its N terminus and the p6 domain at its C terminus) is mixed with nucleic acid, it assembles into virus-like particles (VLPs) in a fully defined system in vitro. However, this assembly is defective in that the radius of curvature of the VLPs is far smaller than that of authentic immature virions. This defect can be corrected to varying degrees by addition of inositol phosphates to the assembly reaction. We have now explored the binding of inositol hexakisphosphate (IP6) to Gag and its effects upon the interactions between Gag protein molecules in solution. Our data indicate that basic regions at both ends of the protein contribute to IP6 binding. Gag is in monomer-dimer equilibrium in solution, and mutation of the previously described dimer interface within its capsid domain drastically reduces Gag dimerization. In contrast, when IP6 is added, Gag is in monomer-trimer rather than monomer-dimer equilibrium. The Gag protein with a mutation at the dimer interface also remains almost exclusively monomeric in IP6; thus the "dimer interface" is essential for the trimeric interaction in IP6. We discuss possible explanations for these results, including a change in conformation within the capsid domain induced by the binding of IP6 to other domains within the protein. The participation of both ends of Gag in IP6 interaction suggests that Gag is folded over in solution, with its ends near each other in three-dimensional space; direct support for this conclusion is provided in a companion manuscript. As Gag is an extended rod in immature virions, this apparent proximity of the ends in solution implies that it undergoes a major conformational change during particle assembly.

Ligand binding: functional site location, similarity and docking.

Computational methods for the detection and characterisation of protein ligand-binding sites have increasingly become an area of interest now that large amounts of protein structural information are becoming available prior to any knowledge of protein function. There have been particularly interesting recent developments in the following areas: first, functional site detection, whereby protein evolutionary information has been used to locate binding sites on the protein surface; second, functional site similarity, whereby structural similarity and three-dimensional templates can be used to compare and classify and potentially locate new binding sites; and third, ligand docking, which is being used to find and validate functional sites, in addition to having more conventional uses in small-molecule lead discovery.