The polypeptide composition of avian infectious bronchitis virus

The virion N protein of infectious bronchitis virus is more phosphorylated than the N protein from infected cell lysates

Because phosphorylation of the infectious bronchitis virus (IBV) nucleocapsid protein (N) may regulate its multiple roles in viral replication, the dynamics of N phosphorylation were examined. ³²P-orthophosphate labeling and Western blot analyses confirmed that N was the only viral protein that was phosphorylated. Pulse labeling with ³²P-orthophosphate indicated that the IBV N protein was phosphorylated in the virion, as well as at all times during infection in either chicken embryo kidney cells or Vero cells. Pulse-chase analyses followed by immunoprecipitation of IBV N proteins using rabbit anti-IBV N polyclonal antibody demonstrated that the phosphate on the N protein was stable for at least 1 h. Simultaneous labeling with ³²P-orthophosphate and ³H-leucine identified a 3.5-fold increase in the ³²P:³H counts per minute (cpm) ratio of N in the virion as compared to the ³²P:³H cpm ratio of N in the cell lysates from chicken embryo kidney cells, whereas in Vero cells the ³²P:³H cpm ratio of N from the virion was 10.5-fold greater than the ³²P:³H cpm ratio of N from the cell lysates. These studies are consistent with the phosphorylation of the IBV N playing a role in assembly or maturation of the viral particle.

The carboxyl-terminal 120-residue polypeptide of infectious bronchitis virus nucleocapsid induces cytotoxic T lymphocytes and protects chickens from acute infection

Specific cytotoxic T-lymphocyte (CTL) responses to nucleocapsid of infectious bronchitis virus (IBV) were identified by using target cells infected with a Semliki Forest virus (SFV) vector. Effector cells for CTL assays were collected from chickens infected with the Gray strain of IBV or inoculated with a DNA plasmid encoding nucleocapsid proteins. IBV-specific CTL epitopes were mapped within the carboxyl-terminal 120 amino acids of the nucleocapsid protein. CTL lysis of target cells infected with SFV encoding nucleocapsid was major histocompatibility complex restricted and mediated by CD8+ T cells. In addition, splenic T cells collected from chickens inoculated in the breast muscle with a DNA plasmid encoding this CTL epitope(s) recognized target cells infected with wild-type virus or an SFV vector encoding nucleocapsid proteins. CTL activity of splenic T cells collected from chicks immunized with a DNA plasmid encoding CTL epitopes was cross-reactive, in that lysis of target cells infected with serologically distinct strains of IBV was dose responsive in a manner similar to that for lysis of target cells infected with the homologous strain of IBV. Furthermore, chickens immunized with a DNA plasmid encoding a CTL epitope(s) were protected from acute viral infection.

A novel protein polymorphism differentiates the California serotype of infectious bronchitis from other serotypes common to California

The California (Cal) serotype of infectious bronchitis virus (IBV) was isolated from layer flocks in southern California in the early 1980s. Since then, it has spread to the broiler-producing regions of central California, where it has been implicated in respiratory disease outbreaks in vaccinated flocks. Lack of a procedure for quickly identifying IBV serotypes in commercial chicken flocks has prevented the causal association of the IBV Cal serotype with respiratory disease outbreaks. A protein polymorphism has been identified in the matrix protein of the Cal serotype; it appears to be unique among other common serotypes of infectious bronchitis virus found in California. This polymorphism can be identified on western blots using raw or concentrated infectious allantoic fluid as the source material. Identification of the Cal serotype and of serotypes in the Mass and Conn groups can be performed rapidly using field samples from suspect flocks. The identification of this polymorphism provides an alternative method for the rapid identification of the Cal serotype of IBV.

Identification of the structural proteins of turkey enteric coronavirus

Coronaviruses in the intestinal contents of turkey poults from Quebec flocks with outbreaks of enteritis were detected by electron microscopy. Five isolates were serially propagated in embryonic turkey eggs by inoculation of clarified intestinal contents into the amniotic cavity. Viral particles contained in the intestinal contents of infected embryos were purified by differential and isopycnic centrifugation in sucrose gradients. Intact virions present in fractions of densities 1.18 to 1.20 g/ml were precipitated with trichloroacetic acid and the protein content was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. At least seven polypeptides with molecular weights ranging from 27,000 to 180,000 were regularly detected after electrophoresis of SDS-solubilized virions. Homologous rabbit antisera to turkey coronaviruses and pooled sera from convalescent turkeys immunochemically stained five polypeptides of apparent molecular weights of 95,000, 72-75,000, 66,000, 52,000 and 27,000. A further polypeptide with a molecular weight of 140,000 appeared in the absence of 2-mercaptoethanol and probably represents a dimer of the 66,000 polypeptide. One Quebec isolate differed from the Minnesota strain by two of its polypeptides, but no antigenic variations could be demonstrated amongst the various isolates either by immuno-electron microscopy, hemagglutination inhibition, or enzyme immuno assays on nitrocellulose.

The molecular biology of coronaviruses

Coronaviruses have recently emerged as an important group of animal and human pathogens that share a distinctive replicative cycle. Some of the unique characteristics in the replication of coronaviruses include generation of a 3' coterminal-nested set of five or six subgenomic mRNAs, each of which appears to direct the synthesis of one protein. Two virus-specific RNA polymerase activities have been identified. Many of the distinctive features of coronavirus infection and coronavirus-induced diseases may result from the properties of the two coronavirus glycoproteins. The intracellular budding site, which may be important in the establishment and maintenance of persistent infections, appears to be due to the restricted intracytoplasmic migration of the E1 glycoprotein, which acts as a matrix-like transmembrane glycoprotein. E1 also exhibits distinctive behavior by self-aggregating on heating at 100°C in sodium dodecyl sulfate (SDS) and by its interaction with RNA in the viral nucleocapsid. The E1 of mouse hepatitis virus (MHV) is an O -linked glycoprotein, unlike most other viral glycoproteins. Thus, the coronavirus system may be a useful model for the study of synthesis, glycosylation, and transport of O -linked cellular glycoproteins.

Structural analysis of virion proteins of the avian coronavirus infectious bronchitis virus

We have found six major polypeptides in virions of the avian coronavirus infectious bronchitis virus grown in tissue culture: four glycoproteins, GP84, GP36, GP31, and GP28, and two non-glycosylated proteins, P51 and P23. In addition, we detected three minor species: two glycoproteins, GP90 and GP59, and one non-glycosylated protein, P14. Two-dimensional tryptic peptide mapping showed that GP36, GP31, GP28, and P23 comprise a group of closely related proteins which we have designated the "P23 family," but that the other proteins are distinct. Analysis by partial proteolytic digestion of P23 family, but that the other proteins are distinct. Analysis by partial proteolytic digestion of the P23 family labeled biosynthetically with [35S] methionine, and P23, labeled with [35S] formyl-methionine by in vitro translation of RNA from infected cells, revealed that the proteins of the P23 family differ in their amino-terminal domains. Similar analysis of GP31 and Gp36 labeled with [3H] mannose showed that the partial proteolytic fragments unique to these proteins were glycosylated. This suggests that differences in glycosylation in the amino-terminal domains contributes to the marked polymorphism os the P23 family. The results are discussed with respect to possible models for synthesis of the virion proteins.

Antigen requirements and specificity of a microplate enzyme-linked immunosorbent assay (ELISA) for detecting infectious bronchitis viral antibodies in chicken serum

The conditions of a rapid, indirect-enzyme linked immunosorbent assay for Infectious Bronchitis Virus (IBV) antibodies have been established. Optimal sensitivity was obtained using 10 micrograms/ml protein concentration of the Mass 41 strain purified from infected allantoic fluid. Specificity was demonstrated with Newcastle Disease Virus (NDV) antigen-antibody system. Negligible crossreactions were observed. After bromelain or lipase treatment IBV had an ELISA reactivity similar to untreated particles suggesting that peripheral constituents of IBV play a minor role when whole virus is absorbed on solid phase. The method offers a simple and specific antibody assay which could be used for the laboratory diagnosis of avian infectious bronchitis.

Avian infectious bronchitis virus structural polypeptides: effect of different conditions of disruption and comparison of different strains and isolates

Variations in the conditions used for disruption of purified virus involving differences in heat treatment and reducing agent concentration produced little affect on the polypeptide profiles of the Massachusetts 41 (M 41) strain of avian infectious bronchitis virus obtained by polyacrylamide gel electrophoresis. Comparisons of the structural polypeptides of 12 IBV isolates, consiting of M 41, six serologically related viruses and representatives of five other serotypes, showed that the viruses could be placed in three groups on the molecular weights of the major glycopolypeptides. These were 31,000 and 86,000 for M 41, the six related viruses and the serologically distinct SE 17; 27,000 and 89,000 for Iowa 97 and Holte and 27,000 and 91,000 for Connecticut and T strain.

Isolation of coronavirus envelope glycoproteins and interaction with the viral nucleocapsid

The two envelope glycoproteins and the viral nucleocapsid of the coronavirus A59 were isolated by solubilization of the viral membrane with Nonidet P-40 at 4 degrees C followed by sucrose density gradient sedimentation. Isolated E2 consisted of rosettes of peplomers, whereas E1, the membrane glycoprotein, was irregular and amorphous. Under certain conditions significant interactions occurred between components of Nonidet P-40-disrupted virions. Incubation of the Nonidet P-40-disrupted virus at 37 degrees C resulted in formation of a complex between one of the viral glycoproteins, E1, and the viral nucleocapsid. This was caused by a temperature-dependent conformational change in E1, resulting in aggregation of E1 and interaction with the viral RNA in the nucleocapsid. E1 also bound rRNA. The E1-nucleocapsid complexes can be distinguished on sucrose and Renografin density gradients from native viral nucleocapsids. The separation of the membrane glycoprotein E1 from the peplomeric glycoprotein E2 permitted preparation of antisera against these isolated proteins. A model is proposed for the arrangement of the three major structural proteins in the coronavirus A59 virion in relation to the viral envelope and RNA.

Pathogenic murine coronaviruses. II. Characterization of virus-specific proteins of murine coronaviruses JHMV and A59V

We have identified nine intracellular virus-specific proteins in cells infected with JHMV or A59V. Seven virus-specific proteins were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and two additional virus-specific proteins were detected by two-dimensional gel electrophoresis. The A59V- and JHMV-specific proteins differ slightly in molecular weight. Four of the nine proteins are structural proteins. The synthesis of the nine virus-specific proteins is noncoordinate with respect to time.

Polypeptide patterns of infectious bronchitis virus serotypes fall into two categories. Brief report

Molecular weights of six major polypeptides of infectious bronchitis virus (IBV) are: 1. 75,000; 2. 50,000; 3. 45,000; 4. 35,000; 5. 28,000 or 24,000, and 6. 22,000 dalton. According to the mobility of protein 5 the polypeptide patterns of IBV serotypes fall into two main categories.

RNA of mouse hepatitis virus

The RNA of mouse hepatitis virus, a coronavirus, was isolated from the virus released early in the infection and analyzed by sucrose gradient sedimentation and electrophoresis. It was found to consist of a piece of single-stranded RNA of about 60S. Its molecular weight was estimated to be 5.4 X 10(6) by electrophoresis in methylmercury-agarose gels. At least one third of the RNA contained polyadenylated sequences. It is, therefore, probably positive stranded. The virus harvested late in the infection contained, in addition to 60S, some 30 to 50S RNA that are possibly degradation products of the 60S RNA. No difference in the electrophoretic behavior could be detected between the RNA isolated from a pathogenic (JHM) and a nonpathogenic (A59) strain.

Polypeptides of the surface projections and the ribonucleoprotein of avian infectious bronchitis virus

Purified avian infectious bronchitis virus was digested with bromelain (0.7 mg/ml), and the surface projections were removed. Polyacrylamide gel electrophoresis of the polypeptides from these bromelain-treated particles showed that VP1, VP2, and VP5 were missing from the seven polypeptides. VP1 to VP7, that were present in untreated virus preparations. Milder bromelain treatment (0.07 mg/ml) left visible surface projections and polypeptides comprising VP1 and VP2 intact, but removed VP5. Thus, there are apparently two types of surface projections on the virus particle. The ribonucleoprotein complex was released from virus particles disrupted with 1% Nonidet P-40. The proportion of VP6 in such preparations was greatly reduced, implying that VP6 is the structural polypeptide of the ribonucleoprotein. Polypeptides VP1, VP2, VP4, and VP5 are glycosylated, but none of the polypeptides contains lipid.

I. Structural proteins: effects of preparative conditions on the migration of protein in polyacrylamide gels

Coronavirus A59 possesses four size classes of structural proteins which have apparent molecular weights measured by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of 23,000 (GP23), 50,000 (VP50), 90,000 (GP90), and 180,000 (GP180). VP50 is the only structural protein which is completely unaffected by protease treatment of intact virions. This species is the most highly labeled by polar amino acids such as glutamic acid and arginine and it is probably associated with the viral nucleocapsid. GP90, GP180, and GP23 are membrane-associated proteins. However, after protease treatment of virions, only 20% of the GP23 molecule is digested, whereas all of the GP90 and GP180 are removed. GP90 and GP180 appear to comprise most of the prominent layer of characteristic projections on the external surface of the viral envelope. The major portion of GP23 is presumed to lie within the lipid envelope, protected from protease digestion. GP23 and the protease resistant portion, p^∗18, exhibit anomalous behavior on SDS-PAGE. After heating to 100° in SDS the electrophoretic mobility of these polypeptides is altered and several new forms of lower mobility are produced. β-Mercaptoethanol and dithiothreitol exaggerate the effects of heating.

Presence of infectious polyadenylated RNA in coronavirus avian bronchitis virus

Avian infectious bronchitis virus (IBV) was radiolabeled for its nucleic acid component by growth in deembryonated chicken eggs. Purified virions of IBV have a buoyant density in linear sucrose gradients of 1.17-1.18 g/cm3 and contain approximately 4% RNA by weight. The genomic ribonucleic acid of IBV shows the following characteristic: (1) It consists of one size class of single-stranded RNA having a molecular weight of 5.5-5.7 x 108 and a sedimentation coefficient of about 48 S; (2) no evidence for subunit structure is apparent since the RNA resolves as a single species with the same electrophoretic mobility in polyacrylamide gels before and after heat denaturation; (3) at least 20–30% of the RNA molecules extracted from purified virions contain sequences of polyadenylic acid of approximately 4 S size; (4) RNA obtained from detergent-disrupted virus particles by phenol-chloroform extraction is infectious for cultures of chick embryo fibroblasts, giving rise to progeny virus which is lethal for embryonated eggs. These findings, together with the observation that IBV virions do not exhibit detectable transcriptase activity, support the conclusion that the genome of this coronavirus acts directly as a messenger RNA in eukaryotic cells.

The polypeptide composition of avain infectious bronchitis virus particles

Egg grown avian infectious bronchitis virus (IBV) centrifuged on sucrose density gradients was found to consist of a major virus peak of density 1.17 to 1.18 g/cm(3). Three different IBV strains were examined and no morphological differences were detected between virus particles of different densities or from different strains. The polypeptides of the different density virus particles from the three IBV strains were analysed on polyacrylamide gels. In all cases 7 polypeptides were observed, although there were differences in the proportions of these polypeptides in particles of different densities and those from the different strains. The polypeptides have been called VP1 (molecular weight 130,000), VP2 (105,000), VP3 (97,000), VP4 (81,000), VP5 (74,000), VP6 (51,000) and VP7 (33,000). Additional polypeptides were produced if slightly harsher treatments were used.

Purification and biophysical properties of human coronavirus 229E

Coronavirus 229E was grown to high titers in diploid fibroblast cells under medium containing twice the normal concentrations of amino acids and vitamins. Growth curves showed maximum virus production at multiplicities of infection of 0.1 and 1; maximum titers of intracellular virus occurred at 22–24 hr and of extracellular virus at 26 hr postadsorption. Tube infectivity titers ranged from 109.0–109.5 TCID50/ml and plaque titers from 1010.2–1010.9 y PFU/ml at the time of peak virus production, when no cytopathology was evident. Virus titer dropped rapidly between 26 and 56 hr, coincident with increasing cytopathology. A single precipitin band was observed in immunodiffusion and immunoelectrophoresis between concentrated virus preparations and antiserum to purified 229E. Neuraminidase and hemagglutinin assays were negative. Virus was purified by two procedures: adsorption to and elution from human “0” erythrocytes and CaHPO4 gel followed by equilibrium sucrose gradient centrifugation, and PEG precipitation followed by equilibrium glycerol/tartrate gradients and rate zonal sucrose or glycerol/tartrate gradients. Final lots of purified virus containing <0.02% of the crude tissue culture proteins had absorption maxima at 256 nm and minima at 241.2 nm and a mean extinction coefficient of E 1cm1% = 54.3 at 256 nm. The fully corrected sedimentation coefficient for the intact virion was S 20,v0 = 381 S. PAGE by different techniques revealed seven polypeptides of mean apparent molecular weights between 16,900 and 196,100. Six contained carbohydrate and one contained lipid. Electropherograms of 3H- and 14C-labeled virus were identical to those of stained gels. Two glycoproteins constituting 25% of the virion protein were identified by bromelin digestion as the spike proteins. The density in sucrose and in potassium tartrate was 1.18 g/ml for the virion and 1.15 g/ml for the “despiked” particle.

Electron microscope observations on the entry of avian infectious bronchitis virus into susceptible cells

Infectious bronchitis virus was observed to enter cells of chicken chorioallantoic membrane by viropexis. There was no support for the suggestion that entry took place by fusion of viral and plasma membranes. The results of electron microscopy showed that virus attachment occurred both at 4 degrees and at 37 degrees C. Viropexis was not observed until the preparations were warmed. Similar results were obtained using chicken kidney cells. Quantitative data obtained from a plaque counting system employing chicken kidney cells indicated that attachment was the same at both temperatures and that some virus particles were taken up at 4 degrees C. Virus uptake was triggered by attachment of the virus to the cell membrane and the subsequent process of virus entry visualised by E. M. appeared to proceed without the involvement of lysosomal enzymes. No intracellular virus was located by electron microscopy in warmed preparations when virus was treated with specific antiserum, either before or after adsorption to the cells.