Amino acid analysis of alfalfa mosaic virus coat proteins: an aid for viral strain identification

Genetic Diversity, Reassortment, and Recombination in Alfalfa mosaic virus Population in Spain

The variability and genetic structure of Alfalfa mosaic virus (AMV) in Spain was evaluated through the molecular characterization of 60 isolates collected from different hosts and different geographic areas. Analysis of nucleotide sequences in four coding regions--P1, P2, movement protein (MP), and coat protein (CP)--revealed a low genetic diversity and different restrictions to variation operating on each coding region. Phylogenetic analysis of Spanish isolates along with previously reported AMV sequences showed consistent clustering into types I and II for P1 and types I, IIA, and IIB for MP and CP regions. No clustering was observed for the P2 region. According to restriction fragment length polymorphism analysis, the Spanish AMV population consisted of seven haplotypes, including two haplotypes generated by reassortment and one involving recombination. The most frequent haplotypes (types for P1, MP, and CP regions, respectively) were I-I-I (37%), II-IIB-IIB (30%), and one of the reassortants, II-I-I (17%). Distribution of haplotypes was not uniform, indicating that AMV population was structured according to the geographic origin of isolates. Our results suggest that agroecological factors are involved in the maintenance of AMV genetic types, including the reassortant one, and in their geographic distribution.

Effect of glutaraldehyde-fixation on the immunogenicity, particle stability and antigenic reactivity of alfalfa mosaic virus, and the specificity of elicited antibodies

Glutaraldehyde-fixation was shown to stabilize the structural integrity of alfalfa mosaic virus (AMV) particles as well as to increase their immunogenicity and antigenic reactivity. The antigenic reactivity of the particles was substantially increased irrespective of whether the antibodies were from animals immunized with native or fixed AMV, or preparations of coat protein subunits isolated from the virus. No significant changes in the antigenic specificity of AMV particles were detected following glutaraldehyde-fixation. Thus it is possible to raise antisera to AMV with higher titres by using fixed virus as immunogen.

The primary structure of the coat protein of alfalfa mosaic virus strain VRU. A hypothesis on the occurrence of two conformations in the assembly of the protein shell

The complete primary structure of the coat protein of strain VRU of alfalfa mosaic virus (AMV) is reported. The strain is morphologically different from all other AMV strains as it contains large amounts of unusually long virus particles. This is caused by structural differences in the coat protein chain. The amino acid sequence has mainly been established by the characterization of peptides obtained after cleavage with cyanogen bromide and digestion with trypsin, chymotrypsin, thermolysin or Staphylococcus aureus protease. The major sequencing technique used was the dansyl-Edman procedure. The VRU coat protein consists of 219 amino acid residues corresponding to a molecular weight of 24056. Compared to the coat protein of strain 425 [Van Beynum et al. (1977) Eur. J. Biochem. 72, 63-78], 15 amino acid substitutions were localized. Most of them have a conservative character and may be explained by single-point mutations. A correction is given for the AMV 425 coat protein: Asn-216 was shown to be Asp-216. The prediction of the secondary structure for the two viral coat proteins was not significantly influenced by the various amino acid substitutions except for the region containing residues 65-100. This led us to the hypothesis that the AMV coat protein may occur in two different conformations favouring its incorporation into either a pentagonal or hexagonal quasi-equivalent position in the lattice of the protein shell. The substitutions in the above-mentioned region of the VRU coat protein may have caused a strong preference for the hexagonal lattice conformation. The model is supported by preliminary sequence data of the same coat protein region in AMV 15/64, a strain morphologically intermediate between 425 and VRU.

Structural studies on the coat protein of alfalfa mosaic virus. The complete primary structure

The complete amino acid sequence of the coat protein of alfalfa mosaic virus (strain 425) is reported. Sequence determinations were mainly performed on peptides obtained from fragmentation by cyanogen bromide and trypsin. Both manual and automatic sequence methods were used. Some refinements of the solid-phase Edman degradation were introduced. The final alignment of the peptides was established by means of alternative cleavage methods, such as limited tryptic digestion of intact virus particles, tryptic digestion after blockage of lysine residues and chymotryptic digestion. The coat protein consists of 220 amino acid residues corresponding to a molecular weight of 24252. A remarkable clustering of basic residues occurs in the N-terminal part of the protein chain. Several internal hydrophobic clusters and a strongly acidic site at the C-terminus can be observed. Two regions of sequence homology (12 residues) were found. Some features of the secondary structure are predicted.