Functional Studies of Ferritin 3-Fold Axis: Effects of Mutations Near Subunit Interaction Sites

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Title: Functional Studies of Ferritin 3-Fold Axis: Effects of Mutations Near Subunit Interaction Sites
Author: Pancorbo, Bruno Marco
Advisors: Dr. J. D. Otvos, Chair
Dr. E. C. Theil, Co-Chair
Dr. D. T. Brown, Member
Dr. H. M. Hassan, Member
Abstract: Ferritin is an iron storage protein whose metabolic importance is reflected in its ubiquitousness in living organisms. Ferritin is a multi-subunit protein (24 subunits) and one of its most interesting features is its 3-dimensional structure: a sphere-like structure with a 4-3-2 symmetry that has a hollow interior where iron is stored. This 3-dimensional structure is highly conserved among ferritins of different living organisms even when the homology of the primary structure of the different ferritins is as low as 22%. Such a degree of structural conservation can only be interpreted as the result of a near perfect balanced between ferritin's structure and function. Among the highly conserved residues are arginine 72 and aspartate 122 which form a salt bridge near the 3-fold interface. To study the importance of these residues in ferritin function, site-directed mutagenesis was used to disrupt and rescue this salt bridge. The properties of the mutants were tested and compared with those of the parent proteins.The greatest difference between mutants and parent proteins was seen in the amount of iron each released. Mutants were found to release a greater percentage of their initial iron than the parents released. Some mutants also showed an increased rate of iron release over the parent proteins, but the effect of the mutation differed depending on the type of subunits used. Another finding was that disruption of the salt bridge caused some of the ferritin subunits to have an increase in volume which seems to correlate with the difference in iron uptake rates for the different ferritin mutants.
Date: 2000-03-01
Degree: MS
Discipline: Biochemistry

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