Characterization of coliphage PR772 and evaluation of its use for virus filter performance testing

Virus filtration is a key clearance unit operation in the manufacture of recombinant protein, monoclonal antibody, and plasma-derived biopharmaceuticals. Recently, a consensus has developed among filter manufacturers and end users about the desirability of a common nomenclature and a standardized test for classifying and identifying virus-retentive filters. The Parenteral Drug Association virus filter task force has chosen PR772 as the model bacteriophage to standardize nomenclature for large-pore-size virus-retentive filters (filters designed to retain viruses larger than 50 to 60 nm in size). Previously, the coliphage PR772 (Tectiviridae family) has been used in some filtration studies as a surrogate for mammalian viruses of around 50 to 60 nm. In this report, we describe specific properties of PR772 critical to the support of its use for the standardization of virus filters. The complete genomic sequence of virulent phage PR772 was determined. Its genome contains 14,946 bp with an overall G+C content of 48.3 mol%, and 32 open reading frames of at least 40 codons. Comparison of the PR772 nucleotide sequence with the genome of Tectiviridae family prototype phage PRD1 revealed 97.2% identity at the DNA level. By dynamic light-scattering analysis, its hydrodynamic diameter was measured as 82 +/- 6 nm, consistent with use in testing large-virus-retentive filters. Finally, dynamic light-scattering analysis of PR772 preparations purified on CsCl gradients showed that the phage preparations are largely monodispersed. In summary, PR772 appears to be an appropriate model bacteriophage for standardization of nomenclature for larger-pore-size virus-retentive filters.     

Age-related decline in carriage of ampicillin-resistant Escherichia coli in young calves

The presence of ampicillin-resistant Escherichia coli (Amp(r) E. coli) in the fecal flora of calves was monitored on a monthly basis in seven cohorts of calves. Calves were rapidly colonized by Amp(r) E. coli, with peak prevalence in cohort calves observed in the 4 months after the calves were born. The prevalence of calves yielding Amp(r) E. coli in cohorts consistently declined to low levels with increasing age of the calves (P < 0.001).     

Nitric oxide formation by Escherichia coli. Dependence on nitrite reductase,the NO-sensing regulator Fnr,and flavohemoglobin Hmp

Nitric oxide (NO) is a key signaling and defense molecule in biological systems. The bactericidal effects of NO produced, for example, by macrophages are resisted by various bacterial NO-detoxifying enzymes, the best understood being the flavohemoglobins exemplified by Escherichia coli Hmp. However, many bacteria, including E. coli, are reported to produce NO by processes that are independent of denitrification in which NO is an obligatory intermediate. We demonstrate using an NO-specific electrode that E. coli cells, grown anaerobically with nitrate as terminal electron acceptor, generate significant NO on adding nitrite. The periplasmic cytochrome c nitrite reductase (Nrf) is shown, by comparing Nrf+ and Nrf- mutants, to be largely responsible for NO generation. Surprisingly, an hmp mutant did not accumulate more NO but, rather, failed to produce detectable NO. Anaerobic growth of the hmp mutant was not stimulated by nitrate, and the mutant failed to produce periplasmic cytochrome(s) c, leading to the hypothesis that accumulating NO in the absence of Hmp inactivates the global anaerobic regulator Fnr by reaction with the [4Fe-4S]2+ cluster (Cruz-Ramos, H., Crack, J., Wu, G., Hughes, M. N., Scott, C., Thomson, A. J., Green, J., and Poole, R. K. (2002) EMBO J. 21, 3235-3244). Fnr thus failed to up-regulate nitrite reductase. The model is supported by the inability of an fnr mutant to generate NO and by the restoration of NO accumulation to hmp mutants upon introducing a plasmid encoding Fnr* (D154A) known to confer activity in the presence of oxygen. A cytochrome bd-deficient mutant retained NO-generating activity. The present study reveals a critical balance between NO-generating and -detoxifying activities during anaerobic growth.     

Dynorphin and the hypothalamo-pituitary-adrenal axis during fetal development

Although dynorphin has long been considered an endogenous opioid peptide with high affinity for the kappa-opioid receptor, its biological function remains uncertain. The high concentration of dynorphin peptides and kappa-opioid receptors in the hypothalamus suggest a possible role for dynorphin in neuroendocrine regulation. This review will summarize evidence that support a role for dynorphin in regulation of the developing hypothalamo-pituitary-adrenal (HPA) axis. Dynorphin can exert dual actions on adrenocorticotropin (ACTH) release: (i) via activation of hypothalamic kappa-opioid receptors leading to release of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), and (ii) via a non-opioid mechanism that involves N-methyl-D-aspartate (NMDA) receptors and prostaglandins, and which is not dependent on CRH or AVP. The primary site of action of dynorphin and NMDA appears to be the fetal hypothalamus or a supra-hypothalamic site. The non-opioid mechanism does not mature until a few days prior to parturition and is active for only the brief perinatal period. In contrast, the opioid mechanism behaves as a constitutive system with sustained activity from prenatal to postnatal life. It is likely that the two mechanisms may respond to different stress stimuli and play a different role during development.     

Introduction of a mutation in the shutter region of antithrombin (Phe77 --> Leu) increases affinity for heparin and decreases thermal stability

The shutter region of serpins consists of a number of highly conserved residues that are critical for both stability and function. Several variants of antithrombin with substitutions in this region are unstable and predispose the carrier to thrombosis. Although most mutations in the shutter region investigated to date are deleterious with respect to serpin stability and function, the substitution of Phe51 by Leu in alpha(1)-antitrypsin results in enhanced stability. Here, we have investigated the effects of introducing an analogous mutation into antithrombin (Phe 77 to Leu). The mutation did not affect the kinetics of interaction with proteases. Strikingly, however, the thermostability of the protein was markedly decreased, with the serpin displaying a 13 degrees C decrease in melting temperature as compared to wild-type recombinant antithrombin. Further studies revealed that in contrast to wild-type antithrombin, the mutant adopted the latent (inactive) conformation upon mild heating. Previous studies on shutter region mutations that destabilize antithrombin revealed that such variants possess enhanced affinity for both heparin pentasaccharide and full-length heparin. The N135A/F77L mutant had unchanged affinity for heparin pentasaccharide, but the affinity for full-length heparin was increased. We suggest that the Phe77Leu mutation causes conformational changes around the top of the D-helix in antithrombin, in particular, to the arginine 132 and 133 residues that may mediate additional antithrombin/heparin interactions. This paper also demonstrates that there are major differences between the shutter regions of antithrombin and alpha(1)-antitrypsin since a stabilizing mutation in antitrypsin has the converse effect in antithrombin.     

Formation of transient oxygen complexes of cytochrome p450 BM3 and nitric oxide synthase under high pressure

The kinetics of formation and transformation of oxygen complexes of two heme-thiolate proteins (the F393H mutant of cytochrome P450 BM3 and the oxygenase domain of endothelial nitric oxide synthase, eNOS) were studied under high pressure. For BM3, oxygen-binding characteristics (rate and activation volume) matched those measured for CO-binding. In contrast, pressure revealed a different CO- and oxygen-binding mechanism for eNOS, suggesting that it is hazardous to take CO-binding as a model for oxygen-binding. With eNOS, a ferric NO complex is formed as an intermediate in the second reaction cycle. Here we report the pressure stability of this compound. Furthermore, in the presence of 4-amino-tetrahydrobiopterin (ABH(4)), an analog to the natural second electron donor tetrahydrobiopterin (BH(4)), biphasic pressure profiles of the oxygen-binding rates were observed, both in the first and the second reaction cycles, indicative of the formation of an additional reaction intermediate. This was confirmed by experiments where ABH(4) was replaced by ABH(2), a cofactor which cannot deliver an electron. Altogether, high pressure appears to be a useful tool to characterize elementary steps in the reaction cycle of heme-thiolate proteins.     

The three-dimensional structure of the core domain of Naf Y from Azotobacter vinelandii determined at 1.8-A resolution

The Azotobacter vinelandii NafY protein (nitrogenase accessory factor Y) is able to bind either to the iron molybdenum cofactor (FeMo-co) or to apodinitrogenase and is believed to facilitate the transfer of FeMo-co into apodinitrogenase. The NafY protein has two domains: an N-terminal domain (residues Met1-Leu98) and a C-terminal domain (residues Glu99-Ser232), referred here to as the "core domain." The core domain of NafY is shown here to be capable of binding the FeMo cofactor of nitrogenase but unable to bind to apodinitrogenase in the absence of the first domain. The three-dimensional molecular structure of the core domain of NafY has been solved to 1.8-A resolution, revealing that the protein consists of a mixed five-stranded beta-sheet flanked by five alpha-helices that belongs to the ribonuclease H superfamily. As such, this represents a new fold capable of binding FeMo-co, where the only previous example was that seen in dinitrogenase.