Cooperative Interactions between Different Classes of Disordered Proteins Play a Functional Role in the Nuclear Pore Complex of Baker’s Yeast
Fig 5
Mean field polymer brush model of the Nuclear Pore Complex.
A: Schematic of a polymer brush structure formed by di-block FG nups. Parameters H, height of the brush; R, radius of the pore; δ, diameter of the “sticky tips”; and d, the average distance between anchor points. Green circles represent the locations at which FG nups are grafted to the pore. B: Free energy of the Nsp1 brush, with and without single-block FG nups present on the pore wall, as a function of brush height for various values of the blob cohesive energy (ϵkBT). Brush height can extend to a maximum of around 22 nm, which is the radius R of the modeled pore minus the size of the sticky tips. Di-block FG nup tip to single-block FG nup cohesion is fixed at ϵs = 6kT. Right: Schematic diagram of the proposed Di-block Copolymer Brush Gate model at various minima of the brush free energy. When particular transport factors are present which are able to outcompete the inter-FG domain “sticky tip” interactions, the brush is able to open up to a new free energy minimum that can accommodate the cargo. When interactions between sticky tips are able to recover into the several kT range, the pore is able to close with a free energy minimum at H ∼ R − δ. We have previously estimated the self interaction energy level of the Nsp1 sticky tip to be 4.7 kT [11], which also sets the energy scale for blob-blob interactions of ϵkT. Single-block FG nups (shrubs) denoted by green compact polymers in the schematic, produce a new minimum in the free energy close to the wall, thus potentially allowing for wide-open states of the brush if tip-tip cohesiveness is lost or reduced.