Quantitative analysis of multi-component spherical virus assembly: scaffolding protein contributes to the global stability of phage P22 procapsids.

摘要: Assembly of the hundreds subunits required to form an icosahedral virus must proceed with exquisite fidelity, and is a paradigm for self-organization complex macromolecular structures. However, mechanism capsid assembly not completely understood any virus. Here we have investigated in vitro phage P22 procapsids using quantitative model specifically developed analyze spherical viruses. Phage are product co-assembly 420 molecules coat protein ∼100–300 scaffolding protein. Scaffolding serves as chaperone part final mature capsid, but essential proper procapsid assembly. show that also affects thermodynamics assembly, first time this analysis has been performed on composed more than one type subunit. Purified proteins were mixed varying ratios procapsids. The reactions allowed reach equilibrium proportion input assembled into or remaining free was determined by size exclusion chromatography SDS-PAGE. results used calculate energy contributions individual proteins. Each subunit found contribute −7.2(±0.1) kcal/mol each −6.1(±0.2) kcal/mol stability procapsid. Because interacts two neighbors, pair-wise energies even less. weak interactions observed likely important control nucleation, since increase affinity between can lead kinetic traps caused formation too many nuclei. In addition, find adjusting molar ratio alter product. When concentration low relative protein, there correspondingly yield very high, nuclei form, leading kinetically trapped intermediates.