A recent field isolate of Sendai virus has a temperature-sensitive HN glycoprotein

The human parainfluenza virus type-1 prototypic strain contains a heat-labile hemagglutinin-neuraminidase protein

The virus yield of human parainfluenza virus type-1 (hPIV-1) in cultured cells at 38 degrees C is reduced more than 100-fold compared to 34 degrees C, while the virus yield of Sendai virus (SV, Enders strain), a murine parainfluenza virus type-1 with high homology to hPIV-1 was almost equal at both temperatures. To understand the basis for the differences in the temperature growth characteristics of the two viruses, we examined the heat-stability of hPIV-1 and SV glycoproteins expressed from cDNAs by pulse-chase experiments. The hemagglutinin-neuraminidase (HN) protein of hPIV-1 was stable after a 6-h chase at 34 degrees C, while at 38 degrees C prominent protein degradation was observed starting at 3 h chase and by 6 h HN was reduced by 65%. In contrast, SV HN protein was stable at both 34 and 38 degrees C. The other hPIV-1 glycoprotein, the fusion (F) protein was stable at both temperatures. To identify the amino acids which are responsible for the heat-lability of hPIV-1 HN, mutant HN proteins were constructed by site-directed mutagenesis. Mutant hPIV-1 HN which had substitutions at positions 461 and 462 became heat-stable at 38 degrees C. These data indicate amino acids around 461 are responsible for the heat-lability of the wild type hPIV-1 HN protein and the reduced yield of the virus at 38 degrees C.

The complete nucleotide sequence of two cold-adapted, temperature-sensitive attenuated mutant vaccine viruses (cp12 and cp45) derived from the JS strain of human parainfluenza virus type 3 (PIV3)

Two cold-passaged mutant vaccine viruses (cp12 and cp45) derived from the JS wild-type (wt) strain of human parainfluenza virus type 3 (PIV3) have been sequenced. These mutant viruses display the cold-adapted (ca), temperature-sensitive (ts), and attenuation (att) phenotypes. Sequence data indicate that both cp12 and cp45 sustained nucleotide substitutions during cold passage and subsequent cloning. Fifteen nucleotide changes were present in cp12 and 18 in cp45. Of these changes, some were present in the sequence of the prototype wt strain (Wash/47885/57) or were non-coding changes present in the open reading frames (ORFs). These were considered unlikely to be of significance in contributing to phenotypic differences between the mutants and the JS wt. There were nine remaining changes in cp12 and eight in cp45 that would most likely contribute to their phenotypes. For cp12, two were non-coding changes in regulatory regions, one in the 3' genome leader and one in the NP gene transcription start signal. The remaining seven changes resulted in amino acid substitutions in NP, F, HN, and L. For cp45, two mutations were in a non-coding regulatory region, the 3' genome leader. The remaining six changes resulted in amino acid substitutions in F, HN, and L. Only one amino acid substitution was conserved between cp12 and cp45 (a valine to alanine change at position 384 of the HN gene). These results should prove useful in the future in understanding the genetic basis of attenuation of the cold-passaged PIV3 candidate vaccine viruses.

Mutation of the HANA protein of Sendai virus by passage in eggs

A study was made to elucidate the effect of host cells on the HANA protein of Sendai virus. Two strains of Sendai virus were isolated from an epidemic in an animal laboratory by inoculating the lung homogenate of a moribund mouse either into LLC-MK2 cells (Oh-L) or into the allantoic cavity of embryonated eggs (Oh-E). Oh-E agglutinated chicken red blood cells at 37 degrees (HA37+), while Oh-L did not (HA37-). When Oh-L was passaged in eggs, conversion of the HA37- virus to the HA37+ virus readily occurred. A single point mutation was recognized on the HANA protein of the HA37+ virus either at position 525 (Gln----Arg) or at position 198 (Leu----Phe). Hl test with monoclonal antibody revealed conformational changes around the receptor binding site. Neuraminidase activity was also affected by these mutations. The changes in these biological activities of the HANA protein seemed to allow the HA37+ virus to replicate in eggs. On the contrary, the HA37+ virus replicates as efficiently as the HA37- virus in LLC-MK2 cells and no reversion to the HA37- virus was observed. The overall results indicate that the passage of Sendai virus in eggs resulted in selection of viruses possessing a specific mutation on the HANA protein. The pneumopathogenicity in mice was not significantly different between the HA37- virus and the HA37+ virus, suggesting the existence of genes other than the HANA gene that determine mouse pathogenicity.

Expression of cDNA encoding the Sendai virus hemagglutinin-neuraminidase gene: characterization of wild-type and mutant gene products

Cloned cDNA encoding the Sendai virus (SV) hemagglutinin-neuraminidase (HN) envelope glycoprotein was expressed in cultured cells in two ways: (I) infection with HN-expressing recombinant vaccinia virus, or (II) transfection with a plasmid with T7 promoter and termination sequences flanking the HN gene, with intracellular T7 RNA polymerase supplied by coinfection with recombinant vaccinia virus that expresses the enzyme. The HN expressed was indistinguishable from the authentic SV protein in antigenicity, cell surface location, and formation of oligomeric structures. In addition, HN expressed from cDNA functioned normally in both hemadsorption and neuraminidase activities. The usefulness of cDNA expression for analyzing HN structure and function was evaluated by mutating the HN cDNA and observing the consequences for HN protein activity. Since previous work indicated that the lysine residue at position 461 is important for the neuraminidase activity of HN, we used site-directed mutation to produce HN protein with this lysine residue changed to glutamic acid. The mutated HN had neuraminidase activity with significantly increased thermal stability, indicating that residue 461 may be essential to the protein's conformation.

Glycosylation of the hemagglutinin-neuraminidase glycoprotein of human parainfluenza virus type 1 affects its functional but not its antigenic properties

The hemagglutinin-neuraminidase (HN) glycoprotein of human parainfluenza virus type 1 (hPIV-1) has been shown to be similar in predicted protein sequence and structure to those of Sendai virus, but it is more highly glycosylated. Because glycosylation can modify protein structure and function, we investigated the effect of glycosylation on the antigenic structure and biological function of the HN of hPIV-1. Antigenic and functional analyses were carried out with purified hPIV-1 virions treated with Endoglycosidase F, which removes carbohydrate moieties, because treatment of hPIV-1-infected LLC-MK2 cells with an inhibitor of glycosylation resulted in virions which were deficient in both HN and F surface glycoproteins. No change in the antigenic structure of the HN of hPIV-1 was detected after carbohydrate removal; epitope recognition by a panel of 7 hPIV-1 HN monoclonal antibodies (MAbs) was unchanged compared to untreated virions. Moreover, there was no change in the cross-reactivity of 8 of 10 Sendai virus HN MAbs, and only a slight change in the remaining 2. Nor did carbohydrate removal appear to affect hemagglutinating or neuraminidase activities; hemagglutination titers with chicken erythrocytes (cRBC) were unchanged, and in vitro neuraminidase activity with a small substrate (N-acetylneuraminlactose) showed only a 20% reduction. However, elution of deglycosylated hPIV-1 from agglutinated cRBC as a result of neuraminidase activity was reduced by 80%. These results suggest that the enzymatic activity of hPIV-1 HN was not directly affected by carbohydrate removal but that the reduction in elution was due to a change in the interaction of the HN with the host receptor. This was further supported by a 2- to 16-fold reduction in the ability of all 7 hPIV-1 HN MAbs to inhibit hemagglutination of deglycosylated hPIV-1 virus. Such a change in HN-host receptor interaction was found to involve a change in receptor specificity because deglycosylated virus was able to fully agglutinate cRBC stripped of receptors required by the native, glycosylated virus. We propose the following model for our results: deglycosylation of the HN of hPIV-1 causes the hemagglutinating portion of the molecule to recognize a new receptor which is not susceptible to enzymatic cleavage by the neuraminidase.

Crystallization of Sendai virus HN protein complexed with monoclonal antibody Fab fragments

The hemagglutinin-neuraminidase (HN) protein of Sendai virus has been isolated from virus particles in a biologically active soluble form after removal by proteolytic digestion of the hydrophobic amino-terminal anchor sequence (S. D. Thompson, W. G. Laver, K. G. Murti, A. Portner, J. Virol., 62, 4653-4660, 1988). The soluble HN exists as both dimers and tetramers, and crystallization trials with each of these forms have so far yielded amorphous material. Dimers complexed with Fab fragments of a monoclonal antibody formed long needle crystals. So far, these are not suitable for X-ray diffraction analysis but the results suggest that HN molecules from paramyxoviruses, even if not crystallizable, may, when complexed with Fab fragments, in some cases yield crystals suitable for X-ray diffraction analysis.