Circular dichroism and structure- function relationships in cloacin DF13- immunity protein complex

Comparison of the circular dichroism (CD), of cloacin-immunity protein complex with that of cloacin and of a mutant cloacin lacking the ability to bind immunity protein, shows that the binding of immunity protein imposes a definite structure on the cloacin molecule. It is discussed that this structure probably is a prerequisite for an effective killing activity of the bacteriocin. The cloacin molecule itself probably has two domains, as was found by limited proteolysis. Comparison of the structure of two of the proteolytic fragments with that of the intact molecule by means of circular dichroism also suggests that cloacin is made up of a part without much periodic structure and of a part with more helicity. The former part being rather sensitive to proteolysis, the latter being comparatively insensitive.