Iron Metabolism

Coordinator: Dr. Beatrice Gorinsky

Serum transferrin is the principle iron transport protein in vertebrates, carrying the metal from sites of absorption, storage and hemoglobin degradation to the cells of the body requiring iron. Transferrin binds iron very strongly but reversibly, protecting the body against the free radical damage associated with free iron. Two techniques have been developed for the removal of iron from transferrin. In vertebrates transferin bound iron is released from transferrin-receptor complexes, following internalisation by endocytosis. The apo-protein is then recycled back to the bloodstream. A number of pathogenic bacteria acquire their supply of iron from serum transferrin through interaction with transferrin binding proteins (TBPs) associated with the cell membrane. The subsequent fate of the transferrin molecule is presently unknown. The dependence of bacteria on this iron supply has raised the possibility of develping a vaccine using TBPs as candidate antigens. Future research will involve the identification of the transferrin binding regions for the receptor and TBPs and the binding regions of the receptor and TBPs of various pathogenic bacteria.

Studies on the glycosylation of transferrins

- Variation in the residues of sugar chains attached to transferrin molecules has been used to identify heavy drinkers. Changes also occur during pregnancy, with aging and in various disease states which need to be analysed as possible physiological indicators.

Non transferrin-bound iron

- It is not known in what form excess iron enters the bloodstream, but is is probably as low molecular weight complexes which may be associated with albumin. Because of the high albumin to transferrin ratio in the blood, it seems likely that initial binding of freshly adsorbed iron, and other metal chelates, such as aluminium, may also be with albumin. Current research using EPR and other spectroscopic techniques has involved the investigation of varying concentrations of serum albumin on combinations of low molecular weight metal complexes using spectroscopic and other techniques, which need to be expanded in future studies.

Molecular recognition and intracellular degradation

- Proteins function through specific interactions with other molecules. These interactions directly involve only a small part of the protein that enables it to recognise or be recognised by other proteins or molecules. Recognition sites are composed of a set of molecular paramaters and these tend to be conserved through evolution if the interactions are important for normal protein function.

In prolonged starvation the degradation rates of 20.30% of cytosolic proteins increase, providing the cell with an emergency supply of amino acids. A molecular chaperone of the hsp70 family is thought to control this degradation by recognising and binding proteins with specific substrate sequences which are then transferred to lysosomes for degradation. The aim of the current research is to determine whether signal sequences identify the regulated proteins and determine the role chaperones and other molecules play in this process. Future work will involve cell biology, biochemistry, protein engineering, molecular modelling and protein crystallisation studies. Protocols will be developed to purify the chaperones and for erythrocyte-mediated microinjection to study the intracellular protein degradation of various native and mutant peptides and proteins. We will examine a number of proteins that should contain signals that consign them to rapid turnover via selective degradation pathways.