Research

Our research group focuses on the study of metal-protein interactions that are relevant in different neurodegenerative and degenerative diseases. We use an array of spectroscopic techniques to study metal ion binding to proteins or peptides that are prone to aggregation, such as β-amyloid peptide (involved in Alzheimer´s disease), α-synuclein (main protein component in Lewy bodies in Parkinson´s disease), prion protein fragments, amyllin (associated to diabetes type 2) and lens crystallin proteins (associated to cataract disease). Our group is interested in elucidating the coordination and redox chemistry associated to these metal-protein interactions, and in understanding how metal binding impacts local protein folding and aggregation propensity. Our research provides further insights into the biological inorganic chemistry of these degenerative diseases, paving the road towards the design of therapeutic strategies that target the role of metal ions in these pathologies. 

Copper-Prion protein interactions

Our research group has advanced the understanding of how Cu binds to the non-octarepeat region of the prion (PrP) protein. The conversion of the cellular prion protein (PrP^C) into the infectious scrapie PrP^Sc isoform is the event associated to the transmission of prion diseases. Several Cu binding sites have been identified in the unstructured N-terminal region of this neuron-anchored protein. Understanding the nature of these binding sites will provide further insights into the cellular function of Cu-PrP interactions and how they impact PrP folding and amyloid aggregation. Our group has elucidated the coordination nature and electronic structure of the Cu binding sites at His96 and His111, which are adjacent to a region that is key for the conversion of PrP into PrP^Sc. The His111 binding site is unique because it contains two Met residues; we have established that these Mets do not participate in Cu(II) binding, but are important for its reduction to Cu(I) and play an important role in Cu(I) coordination. The impact of proteolytic processing of PrP, specifically in the Cu coordination properties of this protein has also been evaluated. Finally, recently we have evaluated the competition for copper ions between the prion protein sites and the amyloid beta peptide, involved in Alzheimer´s disease. 

Metal-induced aggregation of human eye lens crystallin proteins: Relevance to cataracts disease

Cataract disease is caused by formation of light scattering aggregates of human lens proteins called crystallins. We have examined the role of metal ions in the non-amyloid aggregation of human γ-D crystallin, one of the most abundant proteins in the lens. Although these β-sheet rich proteins are highly stable, they may suffer chemical modifications that lead to partially folded species, which are prone to aggregation. These crystallin aggregates are the cause of cataracts disease. We have discovered that essential metal ions, such as Cu(II) and Zn(II), or xenobiotic metals such as Hg(II), can interact with human γ-D crystallin, causing a loss of secondary structure and stability, and thus, inducing its non-amyloid aggregation. This discovery reveals a novel and unexplored bioinorganic facet of cataract disease, and we are currently studying the mechanisms of metal-induced aggregation of this family of lens proteins.

Copper binding to alpha-synuclein, the Parkinson protein

Our research group has also contributed to the understanding of how Cu ions bind to alpha-synuclein (AS), an instrinsically disordered protein that forms amyloid aggregates in Parkinson’s disease. Site-specific interactions of Cu(II) with AS induce its aggregation. We have established that Cu(II) specifically binds with high affinity at the N-terminal region of AS, while His50, the only His in the sequence, provides an anchoring moiety for a second Cu binding site. We have fully elucidated the nature of the coordination mode at the N-terminal region, which is redox-active, and upon reduction, the two Met residues in the vicinity (Met1 and Met5) play a key role in Cu(I) coordination. Also, we have demonstrated that redox cycling of this Cu binding site leads to Met oxidation, supporting a mechanism where Cu-AS interactions lead to site-specific metal-catalyzed oxidation of AS, which in turn impacts amyloid aggregation.

Copper binding to amyloid-beta peptide: Relevance to Alzheimer´s disease. 

Extracellular plaques in Alzheimer’s disease patients are composed of fibrils of amyloid beta peptide (Abeta). Cu-Abeta interactions have been implicated in the amyloid aggregation of this peptide. Two different physiologically relevant Cu coordination modes (mode I and II) have been identified and extensively studied by several research groups. Our work has focused on understanding the redox properties of these two coordination modes. We have established that the differences in their coordination nature have a direct impact in their redox activity: while Mode I displays a reduction potential that would be amenable for oxygen activation and generation of reactive oxygen species, Mode II would be redox-inert under physiological conditions due to its very high reduction potential. The deprotonated amide group in the coordination sphere of Mode II provides a large stabilization of the Cu(II) redox state, while its protonation and the large rearrangement needed to accommodate the Cu(I) redox state are the features that make it possible to detect an intermediate during the electrochemical reduction of this site. Finally, we have also contributed to understanding the effect of Cu(II) ions in the amyoid aggregation of Abeta. We have designed a novel bifunctional non-natural tetrapeptide with the ability to specifically compete for Cu(II) ions with Abeta and to modulate Abeta amyloid fibril formation. Using this peptide tool, we have established that Cu(II) ions take Abeta through a different aggregation pathway that involves the initial formation of very large oligomers that slowly rearrange into amyloid fibrils. Our work provides further insights into the redox properties of Cu-Abeta complexes and how they affect amyloid fibril formation, paving the road for future studies of oxygen activation by Cu-Abeta Mode I, and for the design of bifunctional peptides with therapeutic potential for Alzheimer’s disease.

Copper binding to islet amyloid polypeptide (IAPP) or amylin: Relevance to Type-2 Diabetes.

Amyloid aggregates of IAPP or amylin in the pancreas is one of hallmarks of type-2 diabetes. IAPP is an intrinsically disordered peptide that contains only one His residue, as an anchoring site for metal ions. It has been reported that metal ions, such as Cu(II), inhibit amyloid aggregation of IAPP. Our group has investigated the Cu(II) coordination properties of IAPP, providing important insights into how metal ion binding to IAPP competes with the formation of amyloid fibrils.