Ferritin—phospholipid interaction: A model system for intralysosomal ferritin segregation in iron-overloaded hepatocytes

Abstract

In iron-overloaded hepatocytes, intralysosomal multilamellar structures can be seen on which ferritin particles occasionally form symmetrical arrays. This report describes the formation in vitro of multilamellar phospholipid structures with which ferritin interacts, forming arrays similar to those observed in vivo. Multilamellar phospholipid structures were formed by fusion of small unilamellar vesicles containing acidic phospholipids. Ferritin did not interact with these structures. However, ferritin—liposome symmetrical structures were formed by a two-step procedure: initially small unilamellar vesicles were fused with low calcium concentrations to form vesicles with a diameter of 100–200 nm. Removal of the calcium ions and addition of cationized ferritin to these vesicles induced their fusion, forming large structures composed of up to 15 alternating layers of membranes and regularly spaced ferritin molecules. The arrays were measured and found to be practically identical to those observed in the lysosome. Ferritin—phospholipid association plays a part in the process of lysosomal iron segregation. Ferritin—liposome interaction may serve as a model for certain aspects of ferritin uptake, storage, and release by lysosomal systems.