These changes appear to maximize the toxin's interactions with the cell membrane. The tetramer looks like a windmill or a propeller with a hole in its centre, through which calcium ions probably pass. It seems likely that the 'arms' of the 'windmill' provide surfaces for interactions with cellular signalling machinery. Technically, this is impressive work. The Imperial College researchers were able to resolve the structures using a technique called 'single particle cryo-electron microscopy', working directly from views of the complex in solution.
Samples are frozen and then visualized with an electron beam.
Individual complexes can be observed by this method only if they are above a certain size, and the small toxin dimer is on the borderline for detection. Ushkaryov and coworkers' results suggest a plausible mechanism of alpha-latrotoxin pore formation that should stimulate research into the toxin's many modes of action. More generally their accomplishments are a beautiful illustration of how the function of a molecule can be determined by its structure.