La Doble vida de l’aconitasa: regulació dels nivells de ferro i del metabolisme

Abstract

Iron is an essential element for many biological life forms as part of a large number of prosthetic groups of proteins involved in central cellular processes. The cellular iron content should be maintained within a narrow range to avoid the adverse consequences of iron deficiency or excess. The preservation of cellular iron homeostasis is achieved through coordinated regulation of iron absorption, storage and export by protein IRP1 (Iron Regulatory Protein 1). IRP1 (PDB 3SNP) binds IREs (Iron Responsive Elements) in UTRs of mRNAs that encode proteins involved in the iron recruitment, abduction and export. On the other hand, the cytosolic aconitase (PDB 2B3Y), that contains a cluster [4Fe-4S] at active site, and is a key enzyme in the main energy production pathway being part of the tricarboxylic acid cycle. Aconitase and IRP1 show significant sequence identity and the main hypothesis is that they are both the same protein despite the significant structural and functional differences. The first objective of this study is to determine whether these two proteins are really the same. By using computational methods, the mechanism by which the apo-2B3Y can alter its function, going from a closed conformation with the [4Fe-4S] cluster to an open conformation without cluster, has been studied in detail. To understand the conformational change, molecular dynamics simulations have been performed. Overall, the results obtained in this work have shown that the enzyme cytosolic aconitase evolves towards an open conformation. Thus, concluding that the same protein performs two functions: in low iron conditions it bind to IREs mRNA acting as IRP1 and in high iron conditions assembles [4Fe-4S] cluster acting as cytosolic aconitase. The second aim of the project consists of analysing the effect of mutations on the aconitase conformational change. In this work, several residues from the opening cavity are mutated. The most significant effects corresponds to the double mutation S778A_R780Q which is able to retain the protein in a closed conformation similar to PDB 2B3Y. The residues 778 and 780 play an important role in the transition from cytosolic aconitase to IRP1, being a critical factor in identifying iron-related diseases and in advancing the clinical treatments for such disorders of iron metabolism