Peptide based nanostructures as theranostic tools for biological systems.

Project leaders

Giuseppe Pappalardo, Csilla Kallay

Agreement

UNGHERIA - HAS (MTA) - Accademia Ungherese delle Scienze

Call

CNR/HAS (MTA) 2016-2018

Department

Chemical sciences and materials technology

Thematic area

Chemical sciences and materials technology

Status of the project

New

Research proposal

The collaborative research between the CNR Institute of Biostructures and Bioimaging UOS of Catania (Italy) and the Department of Inorganic and Analytical Chemistry at the University of Debrecen (Hungary) started in 2004 and it is still continuing. Three collaborative research projects (2004-06, 2007-09 and 2010-12) have been completed in this period and the various aspects of the research on the role of metal ions in neurodegenerative diseases were in the focus of the projects. More than 25 common scientific publications have been published on the basis of the collaborative research and many of them were published in definitely highly ranked international journals. Imre Sóvágó was the Hungarian project leader until 2012 but he became an emeritus professor in 2011. Present project leader. Dr.Csilla Kállay is a senior scientist in the same research group with many experience in metallopeptide chemistry providing the sufficient base for successful continuation of the collaboration.
In this research proposal, the collaborating groups will adopt a complementary strategy aimed at designing and characterizing new chemically functionalized peptide systems, also incorporating metal binding sites, for the molecular recognition of amyloid peptides involved in Alzheimer's disease (AD). It is known that some specific amino acid region of the amyloid beta protein represents the hot spots responsible for the pathological self-recognition and fibril growth. The relationship between the mechanism of Abeta aggregation and Alzheimer's disease (AD) is still matter of intense discussion. Since the severity of clinical symptoms in AD patients do not correlate with the presence of fibrillar deposits in the brain it is now widely accepted that small soluble as the primary toxic species. On the other hand, the association of Abeta into either low or high molecular weight oligomers and fibrils, may result in a complex mixture of aggregates whose structure change over time. Such an intricate scenario renders the univocal targeting of the Abeta's harmful molecular species very challenging. As a part of our attempts to get an insight, at the molecular level, into the interaction that lead to the formation of Abeta aggregated species, we have designed a variety of small peptide conjugates able to interfere at the early stage of the Abeta's aggregation process. In particular, the hydrophobic KLVFF sequence of Abeta42 has been chosen because it represents an important element responsible for the aggregation of this peptide.
Compounds that can recognize the different conformational states of the amyloid beta are the best candidates for the development of innovative diagnostic tools. It is important to note that peptide building blocks are currently being explored as a potential material for the design of various nanostructures. The functionality imparted by these biomaterials to the resulting "molecular devices" is particularly amenable to further rational implementation. This can allow, in principle, a step by step construction of more sophisticated systems according to a" bottom-up" experimental approach. As a matter of fact, we have linked a variety of biomolecules to this short pentapeptide to afford novel bio-conjugates displaying an array of interesting properties related to either neuroprotective activity (trehalose-conjugates) or bio-sensing properties (porphyrin conjugates). Our preliminary results obtained on the porphyrin conjugate derivatives, suggest that this class of molecules can respond to different aggregation, yet conformational states, of the amyloid beta peptide through an induced circular dichroism (ICD) or fluorescent signals arising from the incorporated porphyrin moiety. Interestingly the responsiveness of the system depends in vitro on the different experimental conditions, including membrane mimicking environment, different pH values or artificial CSF medium.
In addition, as metal ions can regulate the self-assembly pathway of the amyloid peptide it will be interesting to investigate the sensing properties also in the presence of coordinating metals. In particular to understand the role of metal ions in the response of the nanosensors, both a thermodynamical and electrochemical characterization of the metal complexes are required. The solution equilibrium and spectroscopic studies of metal complexes help to determine the coordination behaviour and the specific metal binding site of the molecules (peptide fragments and the conjugates) and to describe the coordination mode of the metal complexes. On the other hand, the coordination of the metal ions (first of all copper(II)) to the proteins may induce redox processes (oxidation, reduction) as well changing electrochemical properties of metal complexes. It means, that from the characteristic electrochemical parameters the redox activity of the studied complexes can be concluded. Moreover, the electrochemical studies of the peptides and their conjugate complexes give possibility to find the relationship between coordination mode and reducibility, and contrary, the structural information can be concluded from the redox parameters of complexes.
The design, synthesis of peptide conjugates and their biochemical studies will be performed in the research group of Catania, while the thermodynamical and electrochemical part of the research activity will be accomplished at the University of Debrecen, Hungary. Using the natural processes that drive the molecular recognition phenomena in nature as a guide, we expect that these synthesized novel peptide-porphyrin conjugates may be used as bio-sensors for the diagnostic detection of the toxic oligomeric forms of amyloid beta.

Research goals

The main targets of this proposal are:

1) To design and synthesize peptide conjugates assisting the diagnosis and therapy of neurodegenerative diseases.
2) To carry out biophysical characterization of the peptide conjugates as well as their metal complexes formed with Cu(II), Zn(II), Ni(II), Fe(II/III) and Mn(II)
3) To elucidate the molecular mechanism underlying the sensing and cytoprotective abilities of the peptide conjugates.
The results achieved in this project may contribute to shed light into the mechanisms underlying the molecular recognition of toxic oligomers and the role the metal ions play in the recognition process.

Last update: 25/04/2024