Models for the binary complex of bacteriophage T4 gp59 helicase loading protein: gp32 single-stranded DNA-BINDING protein and ternary complex with pseudo-Y junction DNA.

Bacteriophage T4 gp59 helicase assembly protein (gp59) is required for loading of gp41 replicative helicase onto DNA protected by gp32 single-stranded DNA-binding protein. The gp59 protein recognizes branched DNA structures found at replication and recombination sites. Binding of gp32 protein (full-length and deletion constructs) to gp59 protein measured by isothermal titration calorimetry demonstrates that the gp32 protein C-terminal A-domain is essential for protein-protein interaction in the absence of DNA. Sedimentation velocity experiments with gp59 protein and gp32ΔB protein (an N-terminal B-domain deletion) show that these proteins are monomers but form a 1:1 complex with a dissociation constant comparable with that determined by isothermal titration calorimetry. Small angle x-ray scattering (SAXS) studies indicate that the gp59 protein is a prolate monomer, consistent with the crystal structure and hydrodynamic properties determined from sedimentation velocity experiments. SAXS experiments also demonstrate that gp32ΔB protein is a prolate monomer with an elongated A-domain protruding from the core. Fitting structures of gp59 protein and the gp32 core into the SAXS-derived molecular envelope supports a model for the gp59 protein-gp32ΔB protein complex. Our earlier work demonstrated that gp59 protein attracts full-length gp32 protein to pseudo-Y junctions. A model of the gp59 protein-DNA complex, modified to accommodate new SAXS data for the binary complex together with mutational analysis of gp59 protein, is presented in the accompanying article (Dolezal, D., Jones, C. E., Lai, X., Brister, J. R., Mueser, T. C., Nossal, N. G., and Hinton, D. M. (2012) J. Biol. Chem. 287, 18596-18607).

Use of multiple fluorophores for evaluating microvascular permeability in control rats and rats with sepsis.

Capillary leak accompanying systemic inflammatory response conditions is a significant clinical problem. In the present study, we describe and verify a method for studying capillary leak that is based on the injection of proteins that differ significantly in size and have spectrally distinguishable fluorophores. Control (n=11) and post-CLP (caecal ligation and puncture; n=14) Sprague-Dawley rats were injected with tracer amounts of albumin and PEG-Alb [albumin covalently linked to methoxy-poly(ethylene glycol)] labelled with fluorescein and Texas Red. Blood samples were withdrawn between 5 min and 144 h, and the fluorescence of the labelled proteins was determined. The relative retention of the PEG-Alb and albumin was assessed via measurement of the TER (transcapillary escape rate; in %/h) and the t(50%) estimate, defined as the time when the actual concentration reached 50% of its baseline. The concentration-time trends for both albumin and PEG-Alb tracers exhibited two-compartmental behaviour and were analysed using bi-exponential modelling. Retention times were significantly greater for PEG-Alb in both control and CLP rats. TER(PEG-Alb) was significantly lower than TER(albumin) for both control (8.1+/-5.6 compared with 14.8+/-7.1 %/h respectively; P<0.01) and CLP (14.8+/-6.6 compared with 22.5+/-7.3 %/h respectively; P<0.001) rats. The t(50%[PEG-Alb]) was substantially greater than the corresponding t(50%[albumin]) for both control (29.8+/-9.8 compared with 7.2+/-2.0 h respectively; P<0.001) and CLP (12.9+/-5.6 compared with 5.1+/-1.6 h respectively; P<0.001) rats. The result was similar irrespective of the fluorophore-protein combination, validating the multifluorophore technique. In conclusion, the double-fluorophore approach described in the present study may provide the future basis for a method to quantify capillary leak in disease.

Noncanonical function of glutamyl-prolyl-tRNA synthetase: gene-specific silencing of translation.

Aminoacyl tRNA synthetases (ARS) catalyze the ligation of amino acids to cognate tRNAs. Chordate ARSs have evolved distinctive features absent from ancestral forms, including compartmentalization in a multisynthetase complex (MSC), noncatalytic peptide appendages, and ancillary functions unrelated to aminoacylation. Here, we show that glutamyl-prolyl-tRNA synthetase (GluProRS), a bifunctional ARS of the MSC, has a regulated, noncanonical activity that blocks synthesis of a specific protein. GluProRS was identified as a component of the interferon (IFN)-gamma-activated inhibitor of translation (GAIT) complex by RNA affinity chromatography using the ceruloplasmin (Cp) GAIT element as ligand. In response to IFN-gamma, GluProRS is phosphorylated and released from the MSC, binds the Cp 3'-untranslated region in an mRNP containing three additional proteins, and silences Cp mRNA translation. Thus, GluProRS has divergent functions in protein synthesis: in the MSC, its aminoacylation activity supports global translation, but translocation of GluProRS to an inflammation-responsive mRNP causes gene-specific translational silencing.

Plasma expansion by polyethylene-glycol-modified albumin.

Systemic inflammatory response conditions are associated with capillary leak and haemodynamic compromise. Fluid resuscitation to reverse the ensuing hypovolaemia is, however, complicated by the decreased endothelium reflection coefficient to albumin and other colloids. We developed PEG-Alb (albumin covalently linked to polyethylene glycol) as a potential resuscitative agent. PEG was covalently linked to human albumin at multiple sites on the protein. The modified protein was heterogeneous when examined by SDS/PAGE, size-exclusion chromatography and SELDI-TOF MS (surface-enhanced laser-desorption ionization-time of flight MS). Based on size-exclusion chromatography and osmotic pressure data, the effective volume of PEG-Alb is increased 13- to 16-fold compared with unmodified albumin. In an LPS (lipopolysaccharide) model of shock, rats treated with PEG-Alb showed better blood pressure, lower Hct (haematocrit) consistent with haemodilution and less lung injury than rats treated with unmodified albumin or saline. In a CLP (caecal ligation and puncture) model of sepsis, PEG-Alb was more effective than albumin or saline in maintaining blood pressure and in decreasing Hct. When fluorescein-labelled PEG-Alb and Texas Red-labelled albumin were administered to rats with LPS- or CLP-induced shock, PEG-Alb was retained within blood vessels, whereas albumin extravasates into the interstitial space. Based on these data, PEG-Alb appears to be retained within blood vessels in models of capillary leak. PEG-Alb may ultimately be effective in the clinical treatment of shock associated with capillary leak.