Abstract
Hepcidin is a major regulator of iron metabolism. Hepcidin-based therapeutics/diagnostics could play roles in hematology in the future, and thus, hepcidin transport is crucial to understand.
In this study, we identify alpha(2)-macroglobulin (alpha(2)-M) as the specific hepcidin-binding molecule in blood. Interaction of I-125-hepcidin with alpha(2)-M was identified using fractionation of plasma proteins followed by native gradient polyacrylamide gel electrophoresis and mass spectrometry.
Hepcidin binding to nonactivated alpha(2)-M displays high affinity (K-d 177 +/- 27 nM), whereas hepcidin binding to albumin was nonspecific and displayed nonsaturable kinetics. Surprisingly, the interaction of hepcidin with activated alpha(2)-M exhibited a classical sigmoidal binding curve demonstrating cooperative binding of 4 high-affinity (K-d 0.3 mu M) hepcidin-binding sites.
This property probably enables efficient sequestration of hepcidin and its subsequent release or inactivation that may be important for