Sticholysin II, a cytolysin from the sea anemone Stichodactyla helianthus,is a monomer-tetramer associating protein

Sticholysin II (Stn-II) is a pore-forming cytolysin, Stn-II interacts with several supports for size exclusion chromatography, which results in an abn ormal retardation precluding molecular mass calculations. Sedimentation equ ilibrium analysis has revealed that the protein is an associating system at neutral pH, The obtained data fit a monomer-tetramer equilibrium with an a ssociation constant K-4(c) Of 10(9) M-3. The electrophoretic pattern of Stn -II treated with different crosslinking reagents, in a wide range of protei n concentrations, corroborates the existence of tetrameric forms in solutio n. A planar configuration of the four monomers, C4 or D2 symmetry, is propo sed from modelling of the cross-linking data. (C) 1999 Federation of Europe an Biochemical Societies.