Effect of a zwitterionic surfactant (HPS) on the conformation and hemolytic activity of St I and St II, two isotoxins purified from Stichodactyla helianthus.
N-hexadecyl-N-N'-dimethyl-3-ammonio-1-propane-sulfonate (BPS) is a zwitterionic surfactant that readily binds to sticholysins I and II, two sea toxins isolated from Stichodactyla helianthus. The binding constants, evaluated from changes in fluorescence intensities elicited by the surfactant, are approximately 0.5-0.7 microM(-1). The binding of the surfactant changes the conformation of the tertiary protein, without significant changes in its secondary structure, as reported from far-ultraviolet circular dichroism spectra. The changes elicited by HPS lead to loss of the native conformation (as reported from near-ultraviolet circular dichroism spectra) and to a shift of the intrinsic protein fluorescence toward longer wavelengths, an increase in fluorescence intensities and lifetimes, and a faster quenching by acrylamide. All these changes are indicative of a more expanded tertiary conformation. Despite this, the toxins fully retain their hemolytic activities, indicating that spectroscopic changes can be poor predictors of toxin activity.
Lanio
M E
ME
Center for Protein Studies, Faculty of Biology, University of Havana, La Habana, Cuba.
Alvarez
C
C
Martinez
F D
FD
Casallanovo
F
F
Schreier
S
S
Campos
A M
AM
Abuin
E
E
Lissi
E
E
D000818:Animals; D002942:Circular Dichroism; D003063:Cnidaria / Q000737:chemistry*; D006461:Hemolysis / Q000187:drug effects*; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013501:Surface-Active Agents / Q000378:metabolism / Q000494:pharmacology*; D014118:Toxins, Biological / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*
D013501:Surface-Active Agents; D014118:Toxins, Biological