Structural determination of a 670 million year old iron-binding protein

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Iron is a requisite component of most life forms on Earth. The molecule melanotransferrin (MTf) is a member of the transferrin (Tf) family of molecules. It is the most ancient member of the Tf family, dating back over 670 million years. In many species, it exists in both secreted and membrane-anchored forms and has been shown to play a role in transporting iron. Serum Tf carries iron throughout the circulatory system but the unique function(s) and characteristics of MTf in iron transport remain less defined. The 3D structure of MTf has never been determined, and while it is useful to draw comparisons with available crystal structure data for Tf, it is clear that MTf does not bind to the same receptors as Tf. We have evidence that MTf is taken up by a caveolae-dependent pathway rather than the Tf-receptor, clathrin-coated pit mechanism. By comparing the structure of MTf to Tf, we may identify the unique aspects of this ancient iron-binding protein and gain a better understanding of this alternate pathway for iron uptake.s