PMID:22879595

Citation	Padilla-Meier, GP, Gilcrease, EB, Weigele, PR, Cortines, JR, Siegel, M, Leavitt, JC, Teschke, CM and Casjens, SR (2012) Unraveling the role of the C-terminal helix turn helix of the coat-binding domain of bacteriophage P22 scaffolding protein. J. Biol. Chem. 287:33766-80
Abstract	Many viruses encode scaffolding and coat proteins that co-assemble to form procapsids, which are transient precursor structures leading to progeny virions. In bacteriophage P22, the association of scaffolding and coat proteins is mediated mainly by ionic interactions. The coat protein-binding domain of scaffolding protein is a helix turn helix structure near the C terminus with a high number of charged surface residues. Residues Arg-293 and Lys-296 are particularly important for coat protein binding. The two helices contact each other through hydrophobic side chains. In this study, substitution of the residues of the interface between the helices, and the residues in the β-turn, by aspartic acid was used examine the importance of the conformation of the domain in coat binding. These replacements strongly affected the ability of the scaffolding protein to interact with coat protein. The severity of the defect in the association of scaffolding protein to coat protein was dependent on location, with substitutions at residues in the turn and helix 2 causing the most significant effects. Substituting aspartic acid for hydrophobic interface residues dramatically perturbs the stability of the structure, but similar substitutions in the turn had much less effect on the integrity of this domain, as determined by circular dichroism. We propose that the binding of scaffolding protein to coat protein is dependent on angle of the β-turn and the orientation of the charged surface on helix 2. Surprisingly, formation of the highly complex procapsid structure depends on a relatively simple interaction.
Links	PubMed PMC3460473 Online version:10.1074/jbc.M112.393132
Keywords	Amino Acid Sequence; Bacteriophage P22/metabolism; Capsid Proteins/chemistry; Circular Dichroism; Escherichia coli/virology; Models, Molecular; Molecular Conformation; Molecular Sequence Data; Mutagenesis, Site-Directed; Mutation; Oligonucleotides/genetics; Prophages/genetics; Protein Binding; Protein Structure, Secondary; Protein Structure, Tertiary; Static Electricity; Virus Assembly
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
BPP22:VG08		GO:0046797: viral procapsid maturation	ECO:0000315:		P		In figure 2a, the activity of scaffolding protein and mutations is measured via light scattering, and the results show greatly decreased activity compared to the wild type. Figure 2b compares procapsid assembly in wild type and mutated scaffolding proteins via NaCl affinity experiments. While the wild type formed more procapsids with increasing NaCl concentration because "fewer nuclei are formed and reactants are not exhausted, so that complete PCs[procapsids]form," the mutants resulted in decreased procapsid assembly.	complete CACAO 12925

References

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