Kinetics of streptolysin O self-assembly.
Streptolysin O is a member of a family of membrane-damaging toxins that bind to cell membranes containing cholesterol and then polymerize to form large pores. We have examined the kinetics of toxin action using 125I-labelled streptolysin O. Binding of toxin monomers to membranes displays first-order kinetics and is reversible; the rate of desorption from red cells shows a marked dependence on temperature. To study oligomerization, toxin was bound to erythrocytes at 0 degrees C. Oligomer formation was then triggered by a sudden temperature shift and stopped by solubilization of membranes with deoxycholate. While at moderately high streptolysin O concentrations oligomerization behaves as a reaction of second order, the kinetic pattern changes with increasing toxin concentration. We show that this can be accounted for by the assumption of a two-step reaction mechanism: two membrane-bound monomers first associate into a start complex, which then is rapidly extended by the sequential addition of further monomers up to the final oligomer size.
Palmer
M
M
Institute of Medical Microbiology, University of Mainz, Germany.
Valeva
A
A
Kehoe
M
M
Bhakdi
S
S
D000818:Animals; D001426:Bacterial Proteins; D002499:Centrifugation, Density Gradient; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D011817:Rabbits; D013301:Streptolysins / Q000737:chemistry / Q000378:metabolism*
D001426:Bacterial Proteins; D046911:Macromolecular Substances; D013301:Streptolysins; C025964:streptolysin O; D004228:Dithionitrobenzoic Acid