The structure of a highly virulent Theiler's murine encephalomyelitis virus (GDVII) and implications for determinants of viral persistence

GDVII is a highly virulent Theiler's murine encephalomyelitis virus (TMEV) which causes acute encephalitis in mice, while the BeAn and DA strains are the less virulent TMEV which cause chronic demyelinating disease in the central nervous system as a result of persistent infection. Purified GDVII virus isolated from infected BHK-21 cells was crystallized and its structure was determined to 3.5-A resolution by X-ray crystallography. In contrast to other TMEV structures, the VP1 C-terminus of GDVII virus has an ordered conformation that forms a hook over the VP3 knob near the threefold axis. Comparisons with the atomic structures of the less virulent BeAn and DA viruses revealed significant structural variations in a major site (cluster B) on the protruding surface loop puff B of VP2. Puff B is located near the VP3 GH loop region which is structurally analogous to the host receptor attachment site of the major serogroup of human rhinoviruses. Mutations at residue 1101 in VP1 and residue 2141 in VP2, which are also near the VP3 GH loop and adjacent to cluster B, were previously shown to influence persistence of DA virus. These observations indicate that the characteristic interaction with the host receptor through these sites may potentially alter TMEV persistence.

Carcinoma of the minor salivary glands: results of surgery and combined therapy

PURPOSE

This article reports the results of treatment of 7 histologic types of minor salivary gland carcinoma.

PATIENTS AND METHODS

Of 256 cases, local excision was used in 194, extended excision in 62, excision accompanied by neck dissection in 98, and surgery with adjunctive radiation therapy or chemotherapy in 101. Forty-five of the 98 neck dissection cases had cervical node metastases.

RESULTS

Survival rates were analyzed for 233 patients. The 3-year survival rate was (167 of 215) (77.67%), the 5-year survival rate was 134 of 187 (71.76%), and the 10-year survival rate was 79 of 113 (69.91%).

CONCLUSIONS

These data confirm that surgery is still the mode of choice in the treatment of minor salivary gland carcinoma, but a combination with radiation therapy or chemotherapy is advisable in some patients.

A strategy for theoretical binding constant, Ki, calculations for neuraminidase aromatic inhibitors designed on the basis of the active site structure of influenza virus neuraminidase

Neuraminidase (NA) is one of the two major surface antigens of influenza virus. It plays an indispensable role in the release and spread of progeny virus particles during infection. NA inhibitors reduce virus infection in animals. To improve the clinical efficacy of NA inhibitors, we have begun the design of non-carbohydrate inhibitors based on the active site structure of NA. The approach is an iterative process of ligand modeling and electrostatic calculations followed by chemical synthesis of compounds, biological testing, and NA-inhibitor complex structure determination by X-ray crystallography. A strategy has been developed to calculate Ki for newly designed inhibitors. The calculations using the DelPhi program were performed for carbohydrate inhibitors and three preliminary benzoic acid inhibitors of neuraminidase (BANA) that have been synthesized and shown to bind to the active site of NA in the crystal structure. The calculated Kis of these inhibitors have an enlightening agreement with their in vitro biological activities. This demonstrates that the calculations produce informative results on the affinity of modeled inhibitors. GRID maps were also calculated and several pockets were identified for accepting possible new ligands. The calculated Kis for newly designed ligands suggest that these potential compounds will have high inhibitory activities.

4-(Acetylamino)-3-hydroxy-5-nitrobenzoic acid

The 4-(acetylamino)-3-hydroxy-5-nitrobenzoic acid molecule, C9H8N2O6, a designed inhibitor for the influenza virus neuraminidase protein, crystallizes as hydrogen-bonded dimers. The dihedral angles of the substituent groups with respect to the planar phenyl moiety are 5.0 (3) degrees for the carboxyl group, 45.0 (2) degrees for the nitro group and 37.3 (1) degrees for the acetylamino substituent. The crystal structure is stabilized by intermolecular hydrogen bonding.

Crystallization and preliminary X-ray analysis of two density populations of feline calicivirus

Two density populations of full-size feline calicivirus (FCV), the intact infectious particles (P(H)) and the empty capsids (P(L)), have been crystallized using the hanging-drop method. Exposed to high-intensity synchrotron radiation, P(H) and P(L) crystals were shown to diffract X-rays to about 3.0 and 5.5 A resolution, respectively. The P(H) crystal belongs to an orthorhombic crystal system with unit-cell dimensions a = 889.0, b = 995.0, c = 436.6 A. Based on the V(M) value (3.4 A(3) Da(-l)), it was estimated that one crystallographic asymmetric unit of P(H) crystals contains the unique content of an entire virus particle, not necessarily from the same particle. This implies the presence of 60-fold non-crystallographic redundancy. The particle orientation was obtained from a locked rotation function.

Structure-based inhibitors of influenza virus sialidase. A benzoic acid lead with novel interaction

Influenza virus sialidase is a surface enzyme that is essential for infection of the virus. The catalytic site is highly conserved among all known influenza variants, suggesting that this protein is a suitable target for drug intervention. The most potent known inhibitors are analogs of 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (Neu5Ac2en), particularly the 4-guanidino derivative (4-guanidino-Neu5Ac2en). We utilized the benzene ring of 4-(N-acetylamino)benzoic acids as a cyclic template to substitute for the dihydropyran ring of Neu5Ac2en. In this study several 3-(N-acylamino) derivatives were prepared as potential replacements for the glycerol side chain of Neu5Ac2en, and some were found to interact with the same binding subsite of sialidase. Of greater significance was the observation that the 3-guanidinobenzoic acid derivative (equivalent to the 4-guanidino grouping of 4-guanidino-Neu5Ac2en), the most potent benzoic acid inhibitor of influenza sialidase thus far identified (IC50 = 10 microM), occupied the glycerol-binding subsite on sialidase as opposed to the guanidino-binding subsite. This benzoic acid derivative thus provides a new compound that interacts in a novel manner with the catalytic site of influenza sialidase.

Differentiation between homoeologous chromosomes 1A of wheat and 1Am of Triticum monococcum and its recognition by the wheat Ph1 locus

In most allopolyploid plants, only homogenetic chromosome pairing occurs in meiosis, as a result of the recognition of genome differentiation by the genetic system regulating meiotic chromosome pairing. The nature of differentiation between chromosomes of closely related genomes is examined here by investigating recombination between wheat chromosome 1A and the closely related homoeologous chromosome 1Am of Triticum monococcum. The recognition of the differentiation between these chromosomes by the Ph1 locus, which prevents heterogenetic chromosome pairing in wheat, is also investigated. Chromosomes 1A and 1Am are shown to be colinear, and it is concluded that they are differentiated "substructurally." This substructural differentiation is argued to be recognized by the Ph1 locus. In the absence of Ph1, the distribution and frequencies of crossing over between the 1A and 1Am homoeologues were similar to the distribution and frequencies of crossing over between 1A homologues. The cytogenetic and evolutionary significance of these findings is discussed.

Benzoic acid inhibitors of influenza virus neuraminidase

A strategy was developed to design non-carbohydrate inhibitors of influenza virus neuraminidase. Using an iterative cycle of modeling, synthesis, biological testing and X-ray crystallography structure determination, a series of inhibitors based on benzoic acid were produced. The refined structures of three compounds complexed with neuraminidase are reported. The results demonstrate the success of this structure-based drug-design strategy.

Crystallization and preliminary X-ray diffraction studies of the cartilage link protein from bovine trachea

Cartilage extracellular matrix link protein, having molecular mass of approximately 40 kDa, is a metalloprotein that binds divalent cations and is only soluble in low ionic strength solutions. The link protein was purified from bovine trachea and has been crystallized by a vapor diffusion method using PEG 3350 as precipitant. The crystal symmetry is P1, and the unit cell dimensions are a = 43.55, b = 53.11, c = 60.10 A, alpha = 90.44, beta = 106.21, gamma = 101.51 degrees. The VM of 1.8 A3/Da is consistent with the presence of two molecules of the link protein in the asymmetric unit. The crystals diffract X-rays from a synchrotron source to 1.7 A resolution.

Structures of aromatic inhibitors of influenza virus neuraminidase

Neuraminidase (NA), a surface glycoprotein of influenza virus, is a potential target for design of antiinfluenza agents. The crystal structure of influenza virus neuraminidase showed that in the active site 11 residues are universally conserved among all strains known so far. Several potent inhibitors based on the carbohydrate compound 2-deoxy-2,3-didehydro-D-N-acetylneuraminic acid (DANA) have been shown to bind to the conserved active site and to reduce virus infection in animals when administered by nasal spray. Inhibitors of this type are, however, rapidly excreted from physiological systems and may not be effective in order to provide long-time protection. A new class of specific NA inhibitors, which are benzoic acid derivatives, has been designed on the basis of the three-dimensional structure of the NA-DANA complex and modeling of derivatives of 4-(acetylamino)benzoic acid in the NA active site. Intermediates were synthesized and were shown to moderately inhibit the NA activity and to bind to the NA active site as predicted. These rudimentary inhibitors, 4-(acetylamino)-3-hydroxy-5-nitrobenzoic acid, 4-(acetylamino)-3-hydroxy-5-aminobenzoic acid, and 4-(acetylamino)-3-aminobenzoic acid, and their X-ray structures in complexes with N2 (A/Tokyo/3/67) and B/Lee/40 neuraminidases have been analyzed. The coordinates of such inhibitors complexed with NA were used as the starting model for further design of more potent benzoic acid inhibitors. Because the active site residues of NA are invariant, the designed aromatic inhibitors have the potential to become an antiviral drug against all strains of influenza virus.

A sialic acid-derived phosphonate analog inhibits different strains of influenza virus neuraminidase with different efficiencies

A phosphonate analog of N-acetyl neuraminic acid (PANA) has been designed as a potential neuraminidase (NA) inhibitor and synthesized as both the alpha (ePANA) and beta (aPANA) anomers. Inhibition of type A (N2) and type B NA activity by ePANA was approximately a 100-fold better than by sialic acid, but inhibition of type A (N9) NA was only ten-fold better than by sialic acid. The aPANA compound was not a strong inhibitor for any of the NA strains tested. The crystal structures at 2.4 A resolution of ePANA complexed to type A (N2) NA, type A (N9) NA and type B NA and aPANA complexed to type A (N2) NA showed that neither of the PANA compounds distorted the NA active site upon binding. No significant differences in the NA-ePANA complex structures were found to explain the anomalous inhibition of N9 neuraminidase by ePANA. We put forward the hypothesis that an increase in the ePANA inhibition compared to that caused by sialic acid is due to (1) a stronger electrostatic interaction between the inhibitor phosphonyl group and the active site arginine pocket and (2) a lower distortion energy requirement for binding of ePANA.

Characterization of two density populations of feline calicivirus particles

Feline calicivirus (FCV) F9 strain was propagated in Crandall-Reese feline kidney cells. Two density populations of viral particles were observed after equilibrium centrifugation in an isopyknic CsCl gradient. The buoyant density of the heavy particle (PH) is 1.33 g/ml. The light particle (PL), a previously undescribed form of feline calicivirus, has a buoyant density of 1.22 g/ml. The PH and PL presented a similar morphology by electron microscopy. Western blot showed that both PH and PL contained a major polypeptide of the typical FCV capsid protein with a molecular weight of 62,000. Infectivity assay and RNA isolation demonstrated that PH is the intact infectious virion while PL is FCV empty capsid.

Rapid modulation of liver-specific transcription factors after injury

BACKGROUND

The reaction to injury is a well-orchestrated physiologic response involving the coordinated actions of multiple integrated systems. It initially occurs at the molecular level and involves changes in gene transcription. We hypothesized that the molecular mechanisms regulating the generation of an inflammatory response are similar to those orchestrating developmental and tissue-specific expression of proteins and, in the case of the acute phase response, occur through manipulation of liver-specific transcription factors and their binding activity.

METHODS

Female BALB/c mice, 7 to 8 weeks old, were subjected to a 15% body surface area burn. Total and polyadenylated liver RNA was isolated, and Northern blot analysis was performed to determine the kinetics of the acute phase proteins albumin and fibrinogen and the liver-specific transcriptional factors CCAAT-enhancer binding protein (C/EBP) alpha, hepatocyte nuclear factor (HNF)-1 alpha, and HNF-4.

RESULTS

Induction of the injury response was shown by an increase in fibrinogen messenger RNA levels and a decrease in albumin mRNA levels. The liver-specific transcription factor C/EBP alpha decreased after injury and remained significantly lower than control at 3 hours. HNF-4 mRNA levels fell more slowly, reaching significantly lower levels at 6 hours and remaining suppressed at 34 hours. HNF-1 alpha showed the most rapid fall in mRNA levels at 30 minutes after injury and remained significantly below control levels at 34 hours.

CONCLUSIONS

The minimal burn injury model leads to the molecular induction of the acute phase response and induces significant and rapid changes in the liver-specific transcription factors C/EBP alpha, HNF-1 alpha, and HNF-4. These changes may represent a mechanism through which the organ-specific response to injury is mediated.

Structure of influenza virus neuraminidase B/Lee/40 complexed with sialic acid and a dehydro analog at 1.8-A resolution: implications for the catalytic mechanism

Neuraminidase is one of the two glycoprotein spikes protruding from the influenza virus membrane. We have determined by X-ray crystallography the native structure of B/Lee/40 neuraminidase (NA) and the structures of its crystals soaked with a substrate, N-acetylneuraminyllactose (NANL), and an inhibitor, 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (DANA) at 1.8-A resolution. NANL was hydrolyzed by the crystalline NA to generate the product N-acetylneuraminic acid (NANA, also known as sialic acid), which is still able to bind to NA. In the difference Fourier map of the presumed NA-NANA complex, the moiety bound in the active site had a distorted boat conformation of NANA, but there is no significant electron density for O2. The structure of the bound moiety is not identical to that of chemically synthesized DANA soaked into NA crystals. Prolonged incubation of NANA with NA in solution at room temperature produced only a trace amount of DANA as detected by NMR. On the basis of our studies, a mechanism is proposed for the enzymatic hydrolysis by influenza virus neuraminidase.

A reliable amplification technique with single-sided specificity for the isolation of 5' gene-regulating regions

A simple and efficient method is described for the isolation of extension fragments of known DNA sequences by polymerase chain reaction (PCR) using a single specific primer. With this method, size-selected genomic DNA fragments are ligated to a plasmid vector (pGEM-4Z) which contains sequencing primers and the population of chimeric plasmids is used for transforming Escherichia coli. DNA is extracted from an aliquot of the resulting mini-library and PCR performed using a sequence-specific primer and either of the standard sequencing primers of the plasmid vector. This method appears to be more versatile than inverse PCR (IPCR), since: (i) the DNA sequence needed as the specific primer can be as short as about 20 nucleotides (nt); (ii) the DNA templates to be used in PCR are available in high amount, thus facilitating all manipulations; and (iii) if relinearization of the DNA by restriction enzyme digestion is desired before the PCR reaction, many restriction sites can be chosen from the vector polylinker. Using this method, we have isolated the genomic 5' region of the carrot bifunctional dihydrofolate reductase-thymidylate synthase-encoding gene dhfr-ts using a 21-nt sequence of the 5' region of the dhfr-ts cDNA clone as the specific primer.

Transient expression of 3,5,3'-triiodothyronine nuclear receptors in rat oligodendrocytes: in vivo and in vitro immunocytochemical studies

It is generally accepted that the action of thyroid hormones is mediated through specific nuclear receptors. Recent studies have demonstrated the homology of the thyroid receptor with the cellular product of the oncogen v-erbA. So far, two genes have been identified and classified as alpha and beta subtypes. In this study, the expression of nuclear triiodothyronine (T3) receptors (NT3Rs) was examined in secondary cultures containing 85-90% oligodendrocytes (OL) prepared from newborn rat brain primary cultures enriched in OL. These cultures, which are able to produce myelin membranes, were examined by double immunolabelling with a monoclonal antibody (2B3) raised against purified rat liver NT3Rs and with antibodies against two maturation markers of OL: an early marker, galactocerebroside (GC), and myelin basic protein (MBP), which is expressed later than GC. 2B3 recognized three nuclear proteins with the same molecular weights as beta 1, alpha 1, and alpha 2 subtypes with different capacities for binding T3. In 5-day-old OL secondary cultures (25 days, total time in culture), 2B3-NT3R immunoreactivity was located in 77% of morphologically immature OL (GC)+ cells, whereas only 44% of morphologically mature OL were immunoreactive. Only 35% of the MBP+ cells co-expressed NT3Rs. In the corpus callosum of developing rat brain, at all ages studied from 7-60 days postnatal, the total absence of NT3Rs in dark OL (morphologically mature), confirmed by ultrastructural immunocytochemistry, indicates an even more dramatic decrease during maturation. Furthermore, the percentage of medium OL (less mature) stained by 2B3 is reduced by approximately half in 60- compared to 20-day-old rat brain. It is of interest to note that the in vitro observation with maturation markers mirrors the in vivo decrease of NT3R expression during development. It is interesting that NT3Rs are absent in vivo before the critical period of active myelination. These data indicate the presence of a nuclear T3 binding protein in the nuclei of OL at the time of myelination both in vitro and in vivo. The transient expression of these NT3Rs during active myelination argues in favour of a direct effect of thyroid hormones on OL.

Mutations in the poliovirus P1 capsid precursor at arginine residues VP4-ARG34, VP3-ARG223, and VP1-ARG129 affect virus assembly and encapsidation of genomic RNA

To begin to identify poliovirus capsid protein determinants required for assembly and RNA encapsidation, we have addressed the functional significance of three arginine residues of the poliovirus capsid in virus assembly and encapsidation of genomic RNA. These studies were conducted by using a recently described system in which recombinant vaccinia viruses are used to supply poliovirus capsid proteins in trans to a poliovirus subgenomic replicon [D. C. Ansardi, D. C. Porter, and C. D. Morrow (1993) J. Virol. 67, 3684-3690]. Two of the arginine residues, located at position 34 of VP4 (VP4-R034) and position 129 of VP1 (VP1-R129), are located within a cavity on the poliovirus capsid interior, whereas the third arginine, residue 223 of VP3 (VP3-R223), is located at a promoter-protomer interface. Five mutants were constructed by site-directed mutagenesis of poliovirus P1 capsid precursor cDNA to separately encode lysine or glutamine substitutions at VP4-R034 (VP4-R034K, VP4-R034Q), lysine or glutamine substitutions at residue 129 of VP1 (VP1-R129K, VP1-R129Q), or a lysine substitution at residue 223 of VP3 (VP3-R223K). Processed capsid proteins derived from the VP3-R223K, VP1-R129K, and VP1-R129Q mutant precursors were unstable and failed to assemble subviral particles or virions at 37 degrees. The assembly defect for cleavage products of the VP3-R223K precursor was partially overcome at 33 degrees, as empty capsids, but not mature virions, assembled from the mutant capsid subunits at the lower temperature. With regard to the third arginine residue analyzed, VP4-R034, processed capsid proteins derived from both the VP4-R034K and the VP4-R034Q mutant precursors assembled 155S virions at 37 degrees; however, capsid proteins derived from the VP4-R034Q precursor were temperature-sensitive for virion formation at 39.5 degrees. The reduced virion formation at 39.5 degrees was apparently a reflection of a defect in forming assembly competent subunits which also prevented accumulation of surplus VP4-R034Q subunits as empty capsids. By using graphics to display the poliovirus three-dimensional structure, the locations of these residues on the poliovirus capsid interior and their interactions with adjacent amino acids were visualized to provide structural explanations for the observed assembly defects which highlight the important role these residues play in capsid assembly and RNA encapsidation.

Image plane detector spectrophotometer: construction and nightglow observations

Following the theoretical simulation of an image plane detector spectrophotometer (IPDS) presented in a previous paper, a ground-based IPDS for airglow measurements is constructed. This low resolution spectrometer can measure a molecular band spectrum at 12 wavelength positions simultaneously without mechanical scan. The band brightness and rotational temperature of the emitter can be obtained from the measurements. We describe the optical design and calibration of the instrument and present some results of mesospheric nightglow observations. The evaluation and analysis on the performances of the new instrument are also given. The result shows that, although the constructed instrument does not represent the optimized IPDS, the instrument performed reasonably well, and with some improvements the IPDS has great potential of being used to study small-scale oscillations in airglow layers.

Crystallization and preliminary X-ray diffraction studies of Theiler's virus (GDVII strain)

Theiler's murine encephalomyelitis virus (TMEV) is a member of the picornavirus family. Mice infected with TMEV serve as models for the study of human neurological diseases including multiple sclerosis. Preparations of the GDVII strain of Theiler's virus have been crystallized using the hanging drop technique. When exposed to high intensity synchrotron radiation, these monoclinic crystals diffracted X-rays to at least 3.0 A resolution. The unit cell has a C-centered lattice with dimensions: a = 575.2 A, b = 324.0 A and c = 558.4 A, beta = 108.2 degrees. The molecular mass and cell dimensions imply that there is an entire virus particle per asymmetric unit, suggesting the presence of 60-fold non-crystallographic redundancy. This GDVII crystal form appears to be suitable for high-resolution structure determination.

Molecular cloning and analysis of a cDNA coding for the bifunctional dihydrofolate reductase-thymidylate synthase of Daucus carota

Molecular cloning of dihydrofolate reductase-thymidylate synthase (DHFR-TS) of Daucus carota was achieved by immunoscreening of a cDNA library obtaining a 2 kbp clone which contains an open reading frame of 1528 bp. Comparison of the deduced amino acid sequence with those from other sources revealed the presence of motifs typical of DHFR and TS thus confirming the bifunctional nature of the carrot protein. As in other organisms, a higher degree of conservation was observed in the TS domain. Analysis of the dhfr-ts gene content in carrot revealed the presence of several copies per diploid genome.

Molecular and structural basis of hemagglutination in mengovirus

The molecular and structural basis of mengovirus hemagglutination (HA) was investigated by the comparison of nucleotide sequences of the entire capsid coding regions of an HA+ variant, two HA- mutants, 205 and 280, and two HA+ revertants of 205. The mutants were selected after acridine mutagenesis of mengovirus-37A, a heat-stable and HA+ variant that is neurotropic in mice. HA+ revertants of mutant 205 were isolated from brain tissue of mice inoculated with mutant 205. The nucleotide sequences were determined by consensus RNA sequencing using genomic RNA templates from purified virions. Two nucleotide differences were observed in the VP1 coding region of the RNA genomes of mutants 205 and 280 in comparison to the RNA sequences of 37A and the revertants. Interpretation of these data predict substitutions of two consecutive amino acids at residues 1231 (K to R) and 1232 (P to S) of VP1 which form part of the H-I loop of VP1 found at the icosahedral fivefold axis. Analysis of the amino acid substitutions in the context of the three-dimensional structure of the mengovirus-M capsid indicated that hemagglutination most likely involves residues found at the icosahedral fivefold axis and probably does not involve the residues that form the putative cellular receptor binding site (the "pit"). Eleven amino acid differences were observed between the structural proteins of mengovirus-M and 37A, five in VP1, three in VP2, and three in VP3.

Characterization of a gene family encoding abscisic acid- and environmental stress-inducible proteins of alfalfa

The phytohormone abscisic acid (ABA) has been proposed as a common mediator controlling adaptive plant responses to a variety of environmental stresses, including water deficit, salinity, wounding, and low temperature. We have recently isolated three cDNAs, pUM90-1, pUM90-2, and pUM91-4, from a cDNA library of ABA-induced mRNAs of alfalfa. These cDNA clones exhibit a very high degree of sequence homology with one another and sequence similarities with certain regions of several stress- and ABA-inducible genes. The polypeptides encoded by these cDNAs are very rich in glycine (35-40%), histidine (7-15%), asparagine (8-14%), and tyrosine (5-10%) and have no tryptophan and proline. All of the encoded polypeptides contain characteristic tandem repeats comprising glycine residues intercepted with histidine and/or tyrosine. The RNAs corresponding to a representative cDNA, pUM90-1, were induced after treatment of seedlings with low temperature, drought, salt, and wounding stress, but not by heat; the induction was maximal under low temperature treatment. ABA and ABA analog rapidly induced the expression of these genes, whereas gibberellic acid treatment exhibited no induction whatsoever. These genes appear to be specifically induced in the shoot tissues. Analysis of ABA induction of genes corresponding to pUM90-1 in alfalfa seedlings of different age groups demonstrated that these genes were inducible in seedlings/plants of all age groups examined. Taken together these results suggest that these cDNA clones encode a group of proteins that are inducible by ABA and multiple environmental stresses and correspond to a new family of genes of plants, designated as ABA- and environmental stress-inducible genes.

Unusual diffraction of type B influenza virus neuraminidase crystals

An unusual X-ray diffraction pattern by tetragonal crystals of a type B influenza virus neuraminidase was observed in that the odd-l reflections were missing or diffuse while the even-l reflections were sharp and strong. A statistical analysis showed that an error (epsilon) in the spacing of successive planes of neuraminidase molecules was randomly distributed along the c direction, which resulted in such an unusual diffraction pattern. The error epsilon follows the Bernoullian distribution and may be caused by a flexible loop on the top surface of the neuraminidase.

Three-dimensional structure of Theiler murine encephalomyelitis virus (BeAn strain)

Depending on the strain, Theiler murine encephalomyelitis virus (TMEV) may cause acute encephalitis or chronic demyelinating disease, which is associated with viral persistence in mice. Persistent central nervous system infection and demyelination by the less-virulent TMEV has provided a useful animal model for the human demyelinating disease multiple sclerosis. The less-virulent BeAn strain of TMEV was crystallized and its atomic structure was determined by x-ray crystallography. The alpha-carbon coordinates of the closely related Mengo virus were used to calculate the initial phases to 3.5 A resolution and the interpretable electron density map was produced by 10 cycles of 30-fold noncrystallographic molecular replacement averaging. The structure revealed a high degree of overall structural similarity to Mengo virus as well as substantial differences in the surface loops. These structural changes might be correlated with TMEV host-specific recognition, pH-related stability, and neurovirulence.

Enzymatic activity of poliovirus RNA polymerase mutants with single amino acid changes in the conserved YGDD amino acid motif

RNA-dependent RNA polymerases contain a highly conserved region of amino acids with a core segment composed of the amino acids YGDD which have been hypothesized to be at or near the catalytic active site of the molecule. Six mutations in this conserved YGDD region of the poliovirus RNA-dependent RNA polymerase were made by using oligonucleotide site-directed DNA mutagenesis of the poliovirus cDNA to substitute A, C, M, P, S, or V for the amino acid G. The mutant polymerase genes were expressed in Escherichia coli, and the purified RNA polymerases were tested for in vitro enzyme activity. Two of the mutant RNA polymerases (those in which the glycine residue was replaced with alanine or serine) exhibited in vitro enzymatic activity ranging from 5 to 20% of wild-type activity, while the remaining mutant RNA polymerases were inactive. Alterations in the in vitro reaction conditions by modification of temperature, metal ion concentration, or pH resulted in no significant differences in the activities of the mutant RNA polymerases relative to that of the wild-type enzyme. An antipeptide antibody directed against the wild-type core amino acid segment containing the YGDD region of the poliovirus polymerase reacted with the wild-type recombinant RNA polymerase and to a limited extent with the two enzymatically active mutant polymerases; the antipeptide antibody did not react with the mutant RNA polymerases which did not have in vitro enzyme activity. These results are discussed in the context of secondary-structure predictions for the core segment containing the conserved YGDD amino acids in the poliovirus RNA polymerase.

The three-dimensional structure of canine parvovirus and its functional implications

The three-dimensional atomic structure of a single-stranded DNA virus has been determined. Infectious virions of canine parvovirus contain 60 protein subunits that are predominantly VP-2. The central structural motif of VP-2 has the same topology (an eight-stranded antiparallel beta barrel) as has been found in many other icosahedral viruses but represents only about one-third of the capsid protein. There is a 22 angstrom (A) long protrusion on the threefold axes, a 15 A deep canyon circulating about each of the five cylindrical structures at the fivefold axes, and a 15 A deep depression at the twofold axes. By analogy with rhinoviruses, the canyon may be the site of receptor attachment. Residues related to the antigenic properties of the virus are found on the threefold protrusions. Some of the amino termini of VP-2 run to the exterior in full but not empty virions, which is consistent with the observation that some VP-2 polypeptides in full particles can be cleaved by trypsin. Eleven nucleotides are seen in each of 60 symmetry-related pockets on the interior surface of the capsid and together account for 13 percent of the genome.

New crystalline forms of neuraminidase of type B human influenza virus

New crystalline forms of tetrameric neuraminidase heads from two strains (B/Lee/40 and B/mem/89) of type B human influenza virus were obtained and the crystals diffracted using X-rays to 2.5 A resolution without lattice disorder. The new B/Lee/40 crystalline form is tetragonal, space group P42(1)2, with unit cell dimensions a = 123.8 A, c = 71.8 A. The B/mem/89 crystalline form is also tetragonal, space group I422, with unit cell dimensions a = 122.9 A, c = 164.4 A. There is one neuraminidase monomer per asymmetric unit in both forms.

Antigenic, sequence, and crystal variation in influenza B neuraminidase

The neuraminidase (NA) genes of influenza B viruses B/Maryland/59, B/Hong Kong/8/73, B/Singapore/222/79, B/Oregon/5/80, B/USSR/100/83, B/Victoria/3/85, B/Leningrad/179/86, B/Memphis/6/86, and B/Memphis/3/89 have been sequenced. The deduced amino acid sequences show high variability in the stalk domain of the NA, but a surprising degree of sequence conservation in the head region which carries all the antigenic and enzyme activity. The variable region coding for the neuraminidase stalk also translates into a variable section in the overlapping NB polypeptide, which is coded from a second reading frame that overlaps the first 100 amino acids of NA. The influenza B NAs are antigenically distinguishable with monoclonal antibodies in neuraminidase-inhibition tests, even when there is only one amino acid sequence difference. However, seven of nine escape mutants selected with monoclonal antibodies were distinguished only by the antibody used for selection. When NA heads of influenza B viruses are crystallized, there are remarkable differences in crystal morphology between neuraminidases which have very few sequence changes.

Conformational variability of a picornavirus capsid: pH-dependent structural changes of Mengo virus related to its host receptor attachment site and disassembly

The structure of Mengo virus had been determined from crystals grown in the presence of 100 mM phosphate buffer at pH 7.4. It is shown that Mengo virus is poorly infectious at the phosphate concentration similar to that in which it was crystallized. Maximal infectivity is achieved at 10 mM phosphate or less in physiological saline. The phosphate effect is ameliorated when the pH is lowered to 4.6. Although it has not been possible to study the crystal structure of the virus at low phosphate concentrations, it is shown that increasing the Cl- concentration at pH 6.2 or decreasing the pH to 4.6 causes substantial conformational changes confined to the "pit," a deep surface depression. These structural changes involve a movement of the "FMDV loop" (GH loop) in VP1, an ordering of the "VP3 loop" (GH loop in VP3) between 3176 and 3182, the displacement of a bound phosphate near the "FMDV loop" (GH loop in VP1), and movement of the carboxy terminus of VP2. The changes in conformation are correlated with the dissociation of the virion into pentamers at pH 6.2 and 150 mM Cl-. The localization of the conformational changes and the correlated role of the phosphate in controlling infectivity support the hypothesis that the "pit" is the receptor attachment site.

Sindbis virus core protein crystals

The core protein of Sindbis virus has been crystallized. Three different crystal forms have been observed. They diffract variously from 2.5 A to 3.5 A resolution.

Immunocytochemical localization of the nuclear 3,5,3'-triiodothyronine receptor in the adult rat: liver, kidney, heart, lung and spleen

A monoclonal antibody was used for the localization of the nuclear T3 receptor in different tissues of the adult rat: the liver, kidney, heart, lung, spleen, testis, and pituitary. In the liver, the immunoreactivity was found uniformly distributed in the nuclei of hepatocytes. Sections incubated with a control ascitic fluid or with the same ascitic fluid pre-adsorbed with purified receptor showed no specific staining. In the kidney, the immunoreactivity was higher in the epithelial cell of the proximal convoluted tubes and juxtaglomerular cells. In the heart, only the myocardial cells were stained. In the lung, the immunoreactivity was confined to type II pneumocytes and alveolar macrophages. In the spleen, only a few mature lymphocyte and macrophage cell nuclei were stained. These results show that: 1) the abundance of the nuclear T3 correlates with previous studies using hormone binding techniques; 2) the nuclear T3 receptor is selectively located in certain cell types, which possess a precise local function.