title: Bacteriophage P22 scaffolding protein forms oligomers in solution.
abstract: The scaffolding protein of Salmonella typhimurium bacteriophage P22 is a 33.6 kDa protein required both in vivo and in vitro for the polymerization of the viral coat protein into closed T = 7 icosahedral procapsids. In vitro assembly reaction kinetics have previously been found to vary between second and third order with respect to scaffolding protein concentration, suggesting that dimers and/or higher-order oligomers may be the active species in assembly. Analytical ultracentrifugation experiments suggest that scaffolding protein undergoes a rapidly-reversible monomer/dimer/tetramer equilibrium, with higher association constants at 4 degrees C than at 20 degrees C. Under conditions in which in vitro assembly reactions are carried out (30 to 1000 microg/ml scaffolding protein, 20 degrees C), monomers are the predominant species, but the concentration of dimers is significant. A mutant scaffolding protein, R74C/L177I, which forms disulfide-linked dimers, catalyzed procapsid assembly at a higher rate than did the wild-type scaffolding protein; preincubation in dithiothreitol had little effect on the wild-type protein, but greatly reduced the activity of the mutant. These findings suggest that dimers and/or higher-order oligomers of scaffolding protein are active species in the assembly of P22.
authors.affiliation: Dept. of Microbiology, Univ. of Alabama at Birmingham, 35294, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Parker
authors.forename: W F
authors.initials: WF
authors.lastname: Stafford
authors.forename: P E
authors.initials: PE
authors.lastname: Prevelige
mesh_terms: D017100:Bacteriophage P22 / Q000737:chemistry* / Q000502:physiology; D002213:Capsid / Q000096:biosynthesis / Q000737:chemistry*; D007700:Kinetics; D008970:Molecular Weight; D011108:Polymers; D011487:Protein Conformation; D012486:Salmonella typhimurium / Q000821:virology; D014461:Ultracentrifugation; D019065:Virus Assembly / Q000502:physiology
chemical_list: D011108:Polymers