Type III intermediate filaments as novel CoAlation targets

Type III intermediate filaments, such as vimentin, GFAP, and desmin, are involved in cell mechanics, signaling, and stress responses, and are tightly regulated by posttranslational modifications (PTMs). The monomers of these proteins possess a single cysteine residue that plays a key role in network remodeling under oxidative stress. CoAlation is a PTM involving mixed disulfide bond formation between a protein thiol and the coenzyme A (CoA) thiol. Here we aim to investigate the potential CoAlation of vimentin, GFAP, and desmin, and its functional consequences.

CoAlation of type III intermediate filaments and its interplay with other oxidative modifications was assessed in vitro by gel assays and immunological detection, whereas its effect on vimentin filament assembly was evaluated by electron microscopy. In cells, CoAlation was evaluated by CoA immunofluorescence, proximity ligation assay, and/or immunoprecipitation.

CoAlation of vimentin, GFAP, and desmin occurs in vitro and in cells, and is enhanced by oxidants. In the case of vimentin, CoA reciprocally influences other thiol group modifications in vitro, attenuating disulfide-mediated oligomerization and cysteine alkylation. Moreover, in vitro polymerization in the presence of CoA results in shorter vimentin filaments.

We show that vimentin, GFAP, and desmin are CoAlated at their single cysteine residues. Our results suggest that CoAlation may influence filament assembly and compete with other cysteine modifications. Moreover, given its reversibility, CoAlation could potentially play a protective role against more deleterious modifications, such as irreversible cysteine oxidation.