Question

The following passage is excerpted from an essay on structural biology:

For nearly a century, structural biology operated under the central tenet of the structure-function paradigm, which posited that a protein’s biological activity is strictly dictated by a stable, uniquely folded three-dimensional tertiary conformation. However, the identification of intrinsically disordered proteins (IDPs)—macromolecules that lack a fixed equilibrium structure under physiological conditions yet perform critical signaling and regulatory functions—has forced a fundamental reevaluation of this mechanistic dogma. Skeptics of the biological relevance of disorder initially argued that unconstrained polypeptides in vitro merely represented experimental artifacts or transient denatured intermediates destined for rapid proteasomal degradation. To counter this objection, proponents of the disorder paradigm documented that IDPs frequently engage in coupled folding and binding upon encountering their cellular targets, while also utilizing multivalent, flexible interactions to form functional, membraneless liquid condensates. For instance, researchers demonstrated that the nucleoporin proteins lining the nuclear pore complex rely precisely on extended, flexible phenylalanine-glycine repeat domains to create a dynamic, sieve-like hydrogel that selectively filters macromolecular transport without requiring rigid steric lock-and-key docking.

In the context of the passage, the author's reference to the 'nucleoporin proteins lining the nuclear pore complex' serves primarily to: