Bacteriophage F1 Research Articles

Visualizing ATP hydrolysis in a viral DNA-packaging molecular motor

Many DNA viruses encode powerful molecular machines to package viral genome into preformed protein shells. These DNA-packaging motors contain an ATPase module that converts the chemical reaction of ATP hydrolysis to physical motion of DNA. We previously determined the structures of the DNA-packaging motor gp2 of Shigella phage Sf6 in the apo form and in complex with ADP and ATP-gamma-S (Zhao et al, 2013, PNAS, 110, 8075). Here we report the structure of gp2 in complex with its substrate ATP at 2.0 Angstrom resolution. To our knowledge, this is the first time to capture, at high resolution, a precatalytic state for ASCE-superfamily ATPases, which include a large group of nucleic acid helicases and translocases involved in a broad range of cellular and viral processes. The structure reveals the precise architecture of the ATP-bound state of the motor immediately prior to catalysis. Comparison with structures of the apo and ADP-complexed forms unveils motions of the Walker A motif coupled with ATP and Mg2+ binding and ATP hydrolysis. In the Walker B motif, residue E118 undergoes a side chain conformational switching coupled with the ATP hydrolysis, whereas residue E119 locks residue R51 side chain to a conformation that is readily reachable to residue E118 side chain. Residue E121 in the Walker B motif deprotonates a water molecule, which acts as a nucleophile to attack the gamma-phosphorous, leading to ATP hydrolysis. The alpha-helix (residue G182-R194) in the linker domain undergoes a translational motion against the ATPase domain triggered by ATP hydrolysis, serving as a mechanism for translating the energy from the chemical reaction into physical movement of DNA. We further observed the time course of ATP hydrolysis by gp2 by determining structures of gp2:ATP complexes captured at various incubation time. These structures have made it possible to delineate, at atomic detail, the complete cycle of ATP hydrolysis of this viral DNA-packaging molecular motor.

Removal of bacteriophage f2 in water by nanoscale zero-valent iron and parameters optimization using response surface methodology

The presence of pathogenic enteric viruses in water poses a significant risk to human health. Nanoscale zero-valent iron (NZVI) has recently been proposed for various environmental remediation due to its unique characteristics. Bacteriophage f2, which is similar to human enteric pathogenic virus, was used as the model virus to study the virus removal efficiency in the water by NZVI in this study. Response surface methodology (RSM), based on a three-level, four-variable Box–Behnken design, was applied to optimizing the experimental parameters. The results revealed that NZVI showed a brilliant ability in terms of removing bacteriophage f2 and was definitely more efficient than commercial iron particles. The removal rate was increased with the increase of NZVI dose and rotation rate, but decreased with the increase of pH value and virus concentration. The removal process involved reversible adsorption. The bacteriophage f2 with a lower concentration was more sensitive to acid condition. The determination coefficient (R2) for data fitting was 97.66%, which indicated that the model was adequate for prediction. The interaction between NZVI dose and rotation rate had a significant effect on the removal rate of virus, as well as the four independent variables. The optimum values of experimental parameters were as follows: pH value: 5.12, NZVI dose: 49.07 mg L−1, virus concentration: 3.5 × 106 PFU/mL, rotation rate: 148.75 rpm. Under this condition, 5.51 log removal was achieved, which was in close agreement with the value predicted from the proposed model.

Efficient removal of pathogenic bacteria and viruses by multifunctional amine-modified magnetic nanoparticles

A novel amine-functionalized magnetic Fe3O4–SiO2–NH2 nanoparticle was prepared by layer-by-layer method and used for rapid removal of both pathogenic bacteria and viruses from water. The nanoparticles were characterized by TEM, EDS, XRD, XPS, FT-IR, BET surface analysis, magnetic property tests and zeta-potential measurements, respectively, which demonstrated its well-defined core–shell structures and strong magnetic responsivity. Pathogenic bacteria and viruses are often needed to be removed conveniently because of a lot of co-existing conditions. The amine-modified nanoparticles we prepared were attractive for capturing a wide range of pathogens including not only bacteriophage f2 and virus (Poliovirus-1), but also various bacteria such as S. aureus, E. coli O157:H7, P. aeruginosa, Salmonella, and B. subtilis. Using as-prepared amine-functionalized MNPs as absorbent, the nonspecific removal efficiency of E. coli O157:H7 or virus was more than 97.39%, while it is only 29.8% with Fe3O4–SiO2 particles. From joint removal test of bacteria and virus, there are over 95.03% harmful E. coli O157:H7 that can be removed from mixed solution with polyclonal anti-E. coli O157:H7 antibody modified nanoparticles. Moreover, the synergy effective mechanism has also been suggested.

OmpA and OmpC are critical host factors for bacteriophage Sf6 entry in Shigella

Despite being essential for successful infection, the molecular cues involved in host recognition and genome transfer of viruses are not completely understood. Bacterial outer membrane proteins A and C co-purify in lipid vesicles with bacteriophage Sf6, implicating both outer membrane proteins as potential host receptors. We determined that outer membrane proteins A and C mediate Sf6 infection by dramatically increasing its rate and efficiency. We performed a combination of in vivo studies with three omp null mutants of Shigella flexneri, including classic phage plaque assays and time-lapse fluorescence microscopy to monitor genome ejection at the single virion level. Cryo-electron tomography of phage 'infecting' outer membrane vesicles shows the tail needle contacting and indenting the outer membrane. Lastly, in vitro ejection studies reveal that lipopolysaccharide and outer membrane proteins are both required for Sf6 genome release. We conclude that Sf6 phage entry utilizes either outer membrane proteins A or C, with outer membrane protein A being the preferred receptor.

Bacterial Secretins Form Constitutively Open Pores Akin to General Porins

Proteins called secretins form large multimeric complexes that are essential for macromolecular transit across the outer membrane of Gram-negative bacteria. Evidence suggests that the channels formed by some secretin complexes are not tightly closed, but their permeability properties have not been well characterized. Here, we used cell-free synthesis coupled with spontaneous insertion into liposomes to investigate the permeability of the secretin PulD. Leakage assays using preloaded liposomes indicated that PulD allows the efflux of small fluorescent molecules with a permeation cutoff similar to that of general porins. Other secretins were also found to form similar pores. To define the polypeptide region involved in determining the pore size, we analyzed a collection of PulD variants and studied the roles of gates 1 and 2, which were previously reported to affect the pore size of filamentous phage f1 secretin pIV, in assembly and pore formation. Liposome leakage and a novel in vivo assay showed that replacement of the conserved proline residue at position 443 in PulD by leucine increased the apparent size of the pore. The in vitro approach described here could be used to study the pore properties of membrane proteins whose production in vivo is toxic.

Nano-TiO2 membrane adsorption reactor (MAR) for virus removal in drinking water

In order to improve the removal efficiency of virus in drinking water, phage F2, which is similar to human enteric pathogenic virus, was used as the model virus to study the removal efficiency of virus in the water using nano-TiO2-membrane coupling system. The results showed that the adsorption of phage F2 by nanosized TiO2 could reach the adsorption equilibrium in 60min, and the process could follow the Freundlich isotherm (qe=27.4·ce1.24), which is assigned to multilayer adsorption. The kinetic studies showed that the pseudo second-order rate equation could fit the experimental data well. The chemical adsorption was the main mechanism, and the intra particle diffusion was the control step. As for the membrane systems, two different flat membranes PVDF (0.20μm) and PAN (0.05μm) were used, and the removal efficiency of phage F2 was 1.88–2.56 log and 4.78–5.95 log, respectively. As for the coupling systems of nanosized TiO2 and membrane (nano-TiO2-membrane adsorption reactor), the removal efficiency of phage F2 was 3.88 log and 6.40 log, respectively, which was mainly due to the adsorption of nanosized TiO2 and the effective filter cake layer formed on the surface of membrane during operation. The nano-TiO2-membrane adsorption reactor (MAR) achieved not only the high removal efficiency of virus, but also the effective separation and recycle of nanoparticles.

Structures of the phage Sf6 large terminase provide new insights into DNA translocation and cleavage

Many DNA viruses use powerful molecular motors to cleave concatemeric viral DNA into genome-length units and package them into preformed procapsid powered by ATP hydrolysis. Here we report the structures of the DNA-packaging motor gp2 of bacteriophage Sf6, which reveal a unique clade of RecA-like ATPase domain and an RNase H-like nuclease domain tethered by a regulatory linker domain, exhibiting a strikingly distinct domain arrangement. The gp2 structures complexed with nucleotides reveal, at the atomic detail, the catalytic center embraced by the ATPase domain and the linker domain. The gp2 nuclease activity is modulated by the ATPase domain and is stimulated by ATP. An extended DNA-binding surface is formed by the linker domain and the nuclease domain. These results suggest a unique mechanism for translation of chemical reaction into physical motion of DNA and provide insights into coordination of DNA translocation and cleavage in a viral DNA-packaging motor, which may be achieved via linker-domain-mediated interdomain communication driven by ATP hydrolysis.

Function and horizontal transfer of the small terminase subunit of the tailed bacteriophage Sf6 DNA packaging nanomotor

Bacteriophage Sf6 DNA packaging series initiate at many locations across a 2kbp region. Our in vivo studies show that Sf6 small terminase subunit (TerS) protein recognizes a specific packaging (pac) site near the center of this region, that this site lies within the portion of the Sf6 gene that encodes the DNA-binding domain of TerS protein, that this domain of the TerS protein is responsible for the imprecision in Sf6 packaging initiation, and that the DNA-binding domain of TerS must be covalently attached to the domain that interacts with the rest of the packaging motor. The TerS DNA-binding domain is self-contained in that it apparently does not interact closely with the rest of the motor and it binds to a recognition site that lies within the DNA that encodes the domain. This arrangement has allowed the horizontal exchange of terS genes among phages to be very successful.

The 1.58 Å resolution structure of the DNA-binding domain of bacteriophage SF6 small terminase provides new hints on DNA binding

DNA packaging in tailed bacteriophages and in evolutionarily related herpesviruses is controlled by a viral-encoded terminase. As in a number of other phages, in the Bacillus subtilis bacteriophages SF6 and SPP1 the terminase complex consists of two proteins: G1P and G2P. The crystal structure of the N-terminal DNA-binding domain of the bacteriophage SF6 small terminase subunit G1P is reported. Structural comparison with other DNA-binding proteins allows a general model for the interaction of G1P with the packaging-initiation site to be proposed.

The Removal and Inhibitory Effect of CNTs on Model Viruses

Nanomaterial is becoming an important adsorption or disinfection material for removing virus from drinking water. In this study, static and dynamic tests were used to examine adsorption and inhibition characteristics of carbon nanotubes (CNTs) on two model viruses -- f2 and MS2 bacteriophage. Controlling variate method was used to systematically investigate the adsorption kinetics and adsorption isotherms of CNTs on two model viruses; as well as to find the impact of different CNTs dosages on adsorption effect; and then to study the inhibitory effect of CNTs.The results showed that: (1) The adsorption process of f2 and MS2 bacteriophage on CNTs corresponded well with the pseudo-second-order kinetics equation. Time to reach a saturation equilibrium adsorption is about 30min. (2) Both the Langmuir and Freundlich isotherm adequately described two adsorption processes which indicated that the removal mechanism of virus was a mix of monolayer and multilayer adsorption. (3)The dosage of a single removal system should not be too high in practical application. (4) The inhibition of CNTs on model viruses exhibited.

The Evaluation of Photo Catalytic-Membrane Reactor with Nanomaterials for Removing Virus

Nanometer photo catalytic-membrane reactor integrated photo catalytic technology with membrane separation technology was applied to remove virus existing in water. Bacteriophage f2 was used as surrogates for human enteric viruses. Two kinds of nanomaterials (TiO2 and ZnO) were selected as the catalyst. Three kinds of membranes interception performance for virus, adsorption efficiency of nanomaterial for virus, inactivated effect for virus with photo catalysis, and the comprehensive effect to f2 of photo catalytic-membrane reactor were studied under the transmembrane pressure of 20Kpa, with nanomaterial concentration of 100mg/L, light dose of 20mJ/cm2. It showed that the interception effect of flat membrane with casting was the best. the adsorption efficiency of the two kinds of nanomaterials was different, 1.478 lg and 0.201 lg for TiO2 and ZnO, respectively. The removal effect of the photo catalytic oxidation system to f2 was similar, both in 2-3 log. The removal efficiency of the photo catalytic-membrane reactor system has no obvious difference, both in 3-4 log, and it is improved significantly compared to the effect of individual photo catalysis and membrane separation. Further research indicates that: the elimination function of coupling system to f2 includes UV-inactivated, adsorption of nanomaterials, the inactivation of nanomaterials, the effect of oxide moiety which formed after nanomaterials absorbing ultraviolet light and membrane retention.

Translational Control of Protein Synthesis: The Early Years

For the past fifty-five years, much of my research has focused on the function and biogenesis of red blood cells, including the cloning and study of many membrane proteins such as glucose and anion transporters and the erythropoietin receptor. We have also elucidated the mechanisms of membrane insertion, folding, and maturation of many plasma membrane and secreted proteins. Despite all of this work and more, I remain extremely proud of our very early work on the regulation of mRNA translation: work on bacteriophage f2 RNA in the 1960s and on translation of α- and β-globin mRNAs in the early 1970s. Using techniques hopelessly antiquated by today's standards, we correctly elucidated many important aspects of translational control, and I thought readers would be interested in learning how we did these experiments.

Difference in behaviors of F-specific DNA and RNA bacteriophages during coagulation–rapid sand filtration and coagulation–microfiltration processes

Difference in behaviors of F-specific DNA and RNA bacteriophages during coagulation–rapid sand filtration and coagulation–microfiltration (MF) processes were investigated by using river water spiked with F-specific DNA bacteriophage f1 and RNA bacteriophage f2. Because the particle characteristics of f1 (filamentous) and f2 (spherical) are quite different and the surface charge of f1 in the river water was slightly more negative than that of f2, the removal ratios of f1 were approximately 1-log lower than the removal ratio of f2 after any treatment process used in the present study. This result indicates that the behaviors of the two bacteriophages during the treatment processes were different, and that the removal of f1 by the combination of coagulation and filtration processes was more difficult than that of f2. The removal ratios for f1 and f2 were approximately 3-log and 4-log, respectively, in the coagulation–rapid sand filtration process, and 6-log and 7-log, respectively, in the coagulation–MF filtration process. Therefore, as expected, the coagulation–MF process appears to be more effective than the coagulation–rapid sand filtration process for the removal of not only spherical viruses but also filamentous viruses.

Structural and Functional Studies of the Phage Sf6 Terminase Small Subunit Reveal a DNA-Spooling Device Facilitated by Structural Plasticity

In many DNA viruses, genome packaging is initiated by the small subunit of the packaging terminase, which specifically binds to the packaging signal on viral DNA and directs assembly of the terminase holoenzyme. We have experimentally mapped the DNA-interacting region on Shigella virus Sf6 terminase small subunit gp1, which occupies extended surface areas encircling the gp1 octamer, indicating that DNA wraps around gp1 through extensive contacts. High-resolution structures reveal large-scale motions of the gp1 DNA-binding domain mediated by the curved helix formed by residues 54-81 and an intermolecular salt bridge formed by residues Arg67 and Glu73, indicating remarkable structural plasticity underlying multivalent, pleomorphic gp1:DNA interactions. These results provide spatial restraints for protein:DNA interactions, which enable construction of a three-dimensional pseudo-atomic model for a DNA-packaging initiation complex assembled from the terminase small subunit and the packaging region on viral DNA. Our results suggest that gp1 functions as a DNA-spooling device, which may transform DNA into a specific architecture appropriate for interaction with and cleavage by the terminase large subunit prior to DNA translocation into viral procapsid. This may represent a common mechanism for the initiation step of DNA packaging in tailed double-stranded DNA bacterial viruses.

A Single Amino Acid Substitution Changes the Self-Assembly Status of a Type IV Piliation Secretin

Secretins form large multimeric complexes in the outer membranes of many Gram-negative bacteria, where they function as dedicated gateways that allow proteins to access the extracellular environment. Despite their overall relatedness, different secretins use different specific and general mechanisms for their targeting, assembly, and membrane insertion. We report that all tested secretins from several type II secretion systems and from the filamentous bacteriophage f1 can spontaneously multimerize and insert into liposomes in an in vitro transcription-translation system. Phylogenetic analyses indicate that these secretins form a group distinct from the secretins of the type IV piliation and type III secretion systems, which do not autoassemble in vitro. A mutation causing a proline-to-leucine substitution allowed PilQ secretins from two different type IV piliation systems to assemble in vitro, albeit with very low efficiency, suggesting that autoassembly is an inherent property of all secretins.

Identification of a divergent O-acetyltransferase gene oac1b from Shigella flexneri serotype 1b strains

Shigella flexneri is a leading cause of bacterial dysentery in developing countries. Among the 15 known serotypes, four (1b, 3a, 3b and 4b) contain a group 6 epitope due to an acetyl group connected to the O-2 position of rhamnose III on the tetrasaccharide structure of the lipopolysaccharide. O-acetyltransferase encoded by a bacteriophage, Sf6, mediates the acetylation reaction. We found that the oac gene in serotype 1b strains was very different from that in serotypes 3a, 3b and 4b strains and is herein after referred to as oac1b which shares with oac 88%–89% identity at the DNA level and 85% identity at the protein level. Considering that S. flexneri strains of serotypes 1–5 share a recent common ancestry, the divergent oac1b is more likely to have been obtained from outside S. flexneri than to have undergone rapid divergence from the oac gene in the other serotypes (3a, 3b and 4b) within S. flexneri. The cloned oac1b gene was found to perform the same acetylation function as oac. Analysis of the genomic regions flanking oac1b showed that it was present in a prophage on the chromosome and the organizational structure is different from that of phage Sf6. Additionally, phage conversion assay showed that serotype 1b cannot be generated by infecting serotype 1a strains with Sf6. We conclude that oac1b was carried by a non-Sf6 phage and is uniquely present in serotype 1b.

The establishment and application of the method with virus concentration and detection in drinking water

This study aimed to construct an effective method to concentrate and detect virus in drinking water, and human adenovirus pollution status in actual water samples was monitored by constructed method. The concentration efficient of NanoCeram filter for the first concentration with source water and drinking water and the concentration efficient of the different concentrations of PEG 8000 for the second concentration were assessed by spiking f₂ bacteriophage into water samples. The standard of human adenovirus for real-time PCR was constructed by T-A clone. The plasmid obtained was identified through sequence analyzing and consistency check comparing to target gene fragment was conducted by using blast algorithm. Then, real-time PCR was constructed to quantify the concentration of human adenovirus using the plasmid as standard. Water samples were concentrated by using NanoCeram filter on the spot and then concentrated for the second time by PEG/NaCl in 2011. The DNA of concentrated samples were extracted for the quantification of human adenovirus in real-time PCR subsequently to monitor the pollution of human adenovirus in water. For the first concentration by NanoCeram filter, the recovery rates were (51.63 ± 26.60)% in source water and (50.27 ± 14.35)% in treated water, respectively. For the second concentration, the highest recovery rate was reached to (90.09 ± 10.50)% at the concentration of 0.13 kg/L of PEG 8000. The sequence identity score of standard of adenovirus for real time PCR and adenovirus gene was 99%, implying that it can be successfully used to quantification with human adenovirus. The levels of human adenovirus in the water samples sampled in 2011 ranged from 4.13×10³ to 2.20×10⁶ copies/L in source water, while range from 5.57×10² to 7.52×10⁵ copies/L in treated water and the removal efficiency range was (75.49 ± 11.71)%. NanoCeram filers combined with PEG/NaCl was an effective method to concentrate virus in aquatic environment. There was a large number of human adenovirus in source water, and it is not sufficient to remove them thoroughly through conventional water treatment processes.

Structure of the receptor-binding carboxy-terminal domain of bacteriophage T7 tail fibers

The six bacteriophage T7 tail fibers, homo-trimers of gene product 17, are thought to be responsible for the first specific, albeit reversible, attachment to Escherichia coli lipopolysaccharide. The protein trimer forms kinked fibers comprised of an amino-terminal tail-attachment domain, a slender shaft, and a carboxyl-terminal domain composed of several nodules. Previously, we expressed, purified, and crystallized a carboxyl-terminal fragment comprising residues 371-553. Here, we report the structure of this protein trimer, solved using anomalous diffraction and refined at 2 Å resolution. Amino acids 371-447 form a tapered pyramid with a triangular cross-section composed of interlocked β-sheets from each of the three chains. The triangular pyramid domain has three α-helices at its narrow end, which are connected to a carboxyl-terminal three-blade β-propeller tip domain by flexible loops. The monomers of this tip domain each contain an eight-stranded β-sandwich. The exact topology of the β-sandwich fold is novel, but similar to that of knob domains of other viral fibers and the phage Sf6 needle. Several host-range change mutants have been mapped to loops located on the top of this tip domain, suggesting that this surface of the tip domain interacts with receptors on the cell surface.

Intraspecies Biodiversity of the Genetically Homologous Species Brucella microti

Brucellosis is one of the major bacterial zoonoses worldwide. In the past decade, an increasing number of atypical Brucella strains and species have been described. Brucella microti in particular has attracted attention, because this species not only infects mammalian hosts but also persists in soil. An environmental reservoir may pose a new public health risk, leading to the reemergence of brucellosis. In a polyphasic approach, comprising conventional microbiological techniques and extensive biochemical and molecular techniques, all currently available Brucella microti strains were characterized. While differing in their natural habitats and host preferences, B. microti isolates were found to possess identical 16S rRNA, recA, omp2a, and omp2b gene sequences and identical multilocus sequence analysis (MLSA) profiles at 21 different genomic loci. Only highly variable microsatellite markers of multiple-locus variable-number tandem repeat (VNTR) analysis comprising 16 loci (MLVA-16) showed intraspecies discriminatory power. In contrast, biotyping demonstrated striking differences within the genetically homologous species. The majority of the mammalian isolates agglutinated only with monospecific anti-M serum, whereas soil isolates agglutinated with anti-A, anti-M, and anti-R sera. Bacteria isolated from animal sources were lysed by phages F1, F25, Tb, BK2, Iz, and Wb, whereas soil isolates usually were not. Rough strains of environmental origin were lysed only by phage R/C. B. microti exhibited high metabolic activities similar to those of closely related soil organisms, such as Ochrobactrum spp. Each strain was tested with 93 different substrates and showed an individual metabolic profile. In summary, the adaptation of Brucella microti to a specific habitat or host seems to be a matter of gene regulation rather than a matter of gene configuration.

Structural basis for DNA recognition and loading into a viral packaging motor

Genome packaging into preformed viral procapsids is driven by powerful molecular motors. The small terminase protein is essential for the initial recognition of viral DNA and regulates the motor's ATPase and nuclease activities during DNA translocation. The crystal structure of a full-length small terminase protein from the Siphoviridae bacteriophage SF6, comprising the N-terminal DNA binding, the oligomerization core, and the C-terminal β-barrel domains, reveals a nine-subunit circular assembly in which the DNA-binding domains are arranged around the oligomerization core in a highly flexible manner. Mass spectrometry analysis and four further crystal structures show that, although the full-length protein exclusively forms nine-subunit assemblies, protein constructs missing the C-terminal β-barrel form both nine-subunit and ten-subunit assemblies, indicating the importance of the C terminus for defining the oligomeric state. The mechanism by which a ring-shaped small terminase oligomer binds viral DNA has not previously been elucidated. Here, we probed binding in vitro by using EPR and surface plasmon resonance experiments, which indicated that interaction with DNA is mediated exclusively by the DNA-binding domains and suggested a nucleosome-like model in which DNA binds around the outside of the protein oligomer.