Metal Ion Binding of Vimentin Tail Domain Fragments

The intermediate filament (IF) protein vimentin is a critical component of the cell cytoskeleton, yet our mechanistic understanding of head and tail domain function is incomplete. The C-terminal tail domain of vimentin is of increasing interest as it is essential for regulating the structure and mechanical properties of filament networks through interactions with divalent metal ions. However, the molecular basis of tail domain-metal interactions has not been characterized. Here, we analyze the structural and metal-binding properties of the vimentin tail domain. Mass spectrometry, UV-vis, and circular dichroism (CD) spectroscopy reveal binding of divalent copper (Cu(II)) to both a peptide composed of the last 11 residues of the tail domain and the complete, isolated tail domain. Solution nuclear magnetic resonance and CD measurements show that in the absence of Cu(II), the complete vimentin tail domain is primarily disordered and that Cu(II)-binding involves both the last 11 residues and another segment in the middle of the tail domain, leaving the N-terminal portion of the tail domain primarily disordered. Our study provides a Cu(II) binding model for the isolated vimentin tail domain that can assist with the interpretation of Cu(II) mediated effects on vimentin structure in biological contexts.