Practice question

Intermediate filaments are apolar polymers of tetrameric coiled-coil dimers that lack intrinsic nucleotide turnover, so dynamic regulation relies on post-translational modification. Phosphorylation within the N-terminal head domain by mitotic kinases such as Cdk1, Plk1, Aurora B, as well as PKA, PKC and MAP kinases, introduces dense negative charge that disrupts head-to-rod electrostatic interactions essential for filament elongation. The result shifts equilibrium toward soluble tetramers and monomers, enabling mitotic disassembly of vimentin networks and nuclear lamina breakdown at prometaphase, which is required for envelope rupture and chromosome access. Upon mitotic exit phosphatases PP1 and PP2A remove phosphates, promoting rapid reassembly into 10-nm ropes anchored at desmosomes and hemidesmosomes to restore tensile resilience. Phosphorylation also modulates binding to plectin and 14-3-3 adaptors during cell migration. Because assembly requires no ATP or GTP, kinase-phosphatase balance provides primary control over local turnover, solubility, and interaction with signaling scaffolds under stress. Integration with cell cycle kinases, calcium signaling and mechanical cues ensures coordinated remodeling during growth, migration and differentiation.