Functional characterization of Val60, a key residue involved in the membrane-oligomerization of fragaceatoxin C, an actinoporin from Actinia fragacea

•Valine 60 is a crucial residue involved in oligomerization of actinoporins.•Mutations at this position interfere with oligomerization and reduce the overall affinity for membranes.•Actinoporin oligomerization is an enthalpy-driven process. Actinoporins are pore-forming toxins produced by different sea anemones that self-assemble within the membranes of their target cells and compromise their function as a permeability barrier. The recently published three-dimensional structures of two oligomeric complexes formed by fragaceatoxin C point to Val60 as a key residue involved in the oligomerization of the functional pore. To gain insight into the mechanism of toxin oligomerization, different point mutations have been introduced at this position. Functional characterization of the muteins suggests that Val60 represents a hot-spot where the introduction of mutations hinders protein assembly and reduces the overall affinity for membranes.