Chelation and uptake: progress

Using many of the isolation and characterization methods described above, Alison Butler, J. S. Marinez and colleagues have isolated and characterized several siderophores from marine organisms. These are the first marine siderophores to be characterized, and they have structural properties quite different from terrestrial siderophores. Specifically, marine siderophores from both aquachelins and marinobacters have a water-insoluble part (an alpha hydroxy acid at the iron binding site) and a water-soluble part (a lipophilic carbon chain). This unusual structure causes these amphiphlic siderophores to form, in the absence of iron, micelles: clusters of molecules attached together by their fatty-acid tails. Upon binding of Fe(III) micelles come together to form vesicles: spherical shells that are hollow in the middle. This work was published in Science. Here's the reference:

Martinez, J. S., Zhang, G. P., Holt, P. D., Jung, H.-T., Carrano, C. J., Haygood, M. G., Butler, Alison, Self-Assembling Amphiphilic Siderophores from Marine Bacteria. Science 287: 1245-47 (2000).

This work has spawned intense speculation about what role - if any - this amphilic nature plays in mechanisms of iron uptake. Do these micelles and vesicles perform some essential function, or is this behavior an accidental consequence of properties that serve some other function?

We've also made some progress towards understanding the photochemical stability and decomposition of these novel siderophores. But that work hasn't been published so we can't tell you about it yet.

Next project: Intracellular Binding
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