Metal ion binding of vimentin tail domain fragments

The intermediate filament (IF) protein vimentin is widely distributed in various cell types in the body and is vital for the proper maintenance of the cell cytoskeletal architecture, yet an extensive structural characterization of its head and tail domains remains elusive. Alterations in the assembly and organization of vimentin IFs, including filament network reorganization, have been associated with several diseases including cataracts, myopathies, and metastatic cancer. 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, but the molecular basis of these tail domain-metal interactions have not been characterized. In this work, we perform an in-depth analysis of the structural and metal binding properties of fragments of the vimentin tail domain. Mass spectrometry, and UV-Vis and circular dichroism (CD) spectroscopy reveal the direct binding of divalent copper (Cu(II)) to the last 11 residues of the tail domain. Solution nuclear magnetic resonance (NMR) and CD measurements show that in isolation, 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. Aside from these binding sites, Cu(II) does not induce any significant ordering of the tail domain. These findings further support the tail domain serving as a key metal binding region of vimentin and provide new insights into the important interplay between the tail domain and metals in vimentin IF physiology and pathology.