Selective transport control on molecular velcro made from intrinsically disordered proteins

Abstract

The selectivity and speed of many biological transport processes transpire from a 'reduction of dimensionality' that confines diffusion to one or two dimensions instead of three. This behaviour remains highly sought after on polymeric surfaces as a means to expedite diffusional search processes in molecular engineered systems. Here, we have reconstituted the two-dimensional diffusion of colloidal particles on a molecular brush surface. The surface is composed of phenylalanine-glycine nucleoporins (FG Nups)--intrinsically disordered proteins that facilitate selective transport through nuclear pore complexes in eukaryotic cells. Local and ensemble-level experiments involving optical trapping using a photonic force microscope and particle tracking by video microscopy, respectively, reveal that 1-µm-sized colloidal particles bearing nuclear transport receptors called karyopherins can exhibit behaviour that varies from highly localized to unhindered two-dimensional diffusion. Particle diffusivity is controlled by varying the amount of free karyopherins in solution, which modulates the multivalency of Kap-binding sites within the molecular brush. We conclude that the FG Nups resemble stimuli-responsive molecular 'velcro', which can impart 'reduction of dimensionality' as a means of biomimetic transport control in artificial environments.

How to operate a nuclear pore complex by Kap-centric control

“…Kapprobes) on FG layers in the presence of soluble Kapb1. 52 There, we found that the Kap-probes remained stuck to the FG layer (i.e., slow) at low Kapb1 concentrations but exhibited unhindered 2-dimensional diffusion on the layer (i.e., fast) at physiological Kapb1 concentrations. In contrast, non-specific control probes exhibited 3-dimensional diffusion that only transiently impinged the FG layer but did not bind.…”

“…In comparison, weakly bound Kaps might exhibit a 2-dimensional random walk along the luminal "surface" of the translocation corridor owing to the dirty velcro effect with brief excursions into the luminal space. 52 This could in fact expedite transport because the temporal requirement of a 2-dimensional search process for finding the exit of a spatially constrained pore can be considerably less than in 3 dimensions. According to ROD theory, 53,55 the mean diffusion time t for a particle (assuming a constant diffusion coefficient) is related to t 3D » L=b in three dimensions;…”

Limiting the valence: advancements and new perspectives on patchy colloids, soft functionalized nanoparticles and biomolecules

“…[293][294][295][296][298][299][300][301][302][303][304][305][306] A key point is that the interaction between the nanoparticle ligands and the target receptors must be both selective and weak, so that, in analogy to Velcro s , the particle only binds to surfaces that have a high concentration of receptors. 307,308 Currently, coatings targeting cancers are identified mainly through large trial and error screenings with limited help from computational modelling, and without specific design to control the binding affinity. The key to the realization of velcro-like particles is in the design of both the binding strength and specificity of the ligand-receptor bonds 293,307 as well as the control over the geometrical distribution of the ligands on the surface of the nanoparticles.…”

“…307,308 Currently, coatings targeting cancers are identified mainly through large trial and error screenings with limited help from computational modelling, and without specific design to control the binding affinity. The key to the realization of velcro-like particles is in the design of both the binding strength and specificity of the ligand-receptor bonds 293,307 as well as the control over the geometrical distribution of the ligands on the surface of the nanoparticles. Proteins are an optimal choice as ligands since they offer excellent control over binding selectivity and can be chosen so as to minimize the interference with normal cell function.…”

Nucleocytoplasmic Transport: A Paradigm for Molecular Logistics in Artificial Systems

“…[60] FG Nup-functionalized surfaces have also been shown to reconstitute selective transport in two dimensions. [61] Accordingly, this presents a molecular logistics paradigm for regulating transport and communication between artificial organelles, i.e. so-called 'artificial nuclei', …”