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Structure and stability of icosahedral particles of a covalent coat protein dimer of bacteriophage MS2.

ABSTRACT: Particles formed by the bacteriophage MS2 coat protein mutants with insertions in their surface loops induce a strong immune response against the inserted epitopes. The covalent dimers created by fusion of two copies of the coat protein gene are more tolerant to various insertions into the surface loops than the single subunits. We determined a 4.7-A resolution crystal structure of an icosahedral particle assembled from covalent dimers and compared its stability with wild-type virions. The structure resembled the wild-type virion except for the intersubunit linker regions. The covalent dimer orientation was random with respect to both icosahedral twofold and quasi-twofold symmetry axes. A fraction of the particles was unstable in phosphate buffer because of assembly defects. Our results provide a structural background for design of modified covalent coat protein dimer subunits for use in immunization.

SUBMITTER: Plevka P

PROVIDER: S-EPMC2776953 | biostudies-literature | 2009 Aug

REPOSITORIES: biostudies-literature

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Structure and stability of icosahedral particles of a covalent coat protein dimer of bacteriophage MS2.

Plevka Pavel P Tars Kaspars K Liljas Lars L

Protein science : a publication of the Protein Society 20090801 8

Particles formed by the bacteriophage MS2 coat protein mutants with insertions in their surface loops induce a strong immune response against the inserted epitopes. The covalent dimers created by fusion of two copies of the coat protein gene are more tolerant to various insertions into the surface loops than the single subunits. We determined a 4.7-A resolution crystal structure of an icosahedral particle assembled from covalent dimers and compared its stability with wild-type virions. The struc ...[more]

PMID: 19521994

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Project description:Icosahedral virus assembly requires a series of concerted and highly specific protein-protein interactions to produce a proper capsid. In bacteriophage P22, only coat protein (gp5) and scaffolding protein (gp8) are needed to assemble a procapsid-like particle, both in vivo and in vitro. In scaffolding protein's coat binding domain, residue R293 is required for procapsid assembly, while residue K296 is important but not essential. Here, we investigate the interaction of scaffolding protein with acidic residues in the N-arm of coat protein, since this interaction has been shown to be electrostatic. Through site-directed mutagenesis of genes 5 and 8, we show that changing coat protein N-arm residue 14 from aspartic acid to alanine causes a lethal phenotype. Coat protein residue D14 is shown by cross-linking to interact with scaffolding protein residue R293 and, thus, is intimately involved in proper procapsid assembly. To a lesser extent, coat protein N-arm residue E18 is also implicated in the interaction with scaffolding protein and is involved in capsid size determination, since a cysteine mutation at this site generated petite capsids. The final acidic residue in the N-arm that was tested, E15, is shown to only weakly interact with scaffolding protein's coat binding domain. This work supports growing evidence that surface charge density may be the driving force of virus capsid protein interactions.Bacteriophage P22 infects Salmonella enterica serovar Typhimurium and is a model for icosahedral viral capsid assembly. In this system, coat protein interacts with an internal scaffolding protein, triggering the assembly of an intermediate called a procapsid. Previously, we determined that there is a single amino acid in scaffolding protein required for P22 procapsid assembly, although others modulate affinity. Here, we identify partners in coat protein. We show experimentally that relatively weak interactions between coat and scaffolding proteins are capable of driving correctly shaped and sized procapsids and that the lack of these proper protein-protein interfaces leads to aberrant structures. The present work represents an important contribution supporting the hypothesis that virus capsid assembly is governed by seemingly simple interactions. The highly specific nature of the subunit interfaces suggests that these could be good targets for antivirals.

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Structure and stability of icosahedral particles of a covalent coat protein dimer of bacteriophage MS2.

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Structure and stability of icosahedral particles of a covalent coat protein dimer of bacteriophage MS2.

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