APPLIED CHIROPTICAL SPECTROSCOPY

The main field of chiroptical spectroscopy is the investigation of the steric structure of biopolymers such as proteins and nucleic acids. Circular dichroism (CD) is a phenomenon that results when chromophores in an asymmetrical environment interact with polarized light. In proteins the major optically active groups are the amide bonds of the peptide backbone. The far-UV CD is generally reflective of the backbone conformation and different secondary structures in polypeptides and proteins give characteristic far-UV CD spectra. CD is a simple and quick method, its time-scale is below the femtosecond region. Due to the low time-scale, any CD spectrum can be resolved into the component spectra of the main conformer types (α-helix, β-sheet, random, etc.). This method can also be successfully combined with other vibrational spectroscopic methods of similar time-scale [Fourier transform infrared (FTIR), Raman, vibrational circular dichroism].

Recently several studies have been performed in national and international cooperations, the most important are the following:

• Aggregation of Aβ(1-42) amyloid peptide in the presence of short peptides. One of the most characteristic pathological markers of Alzheimer’s disease is the accumulation of the neurotoxic amyloid polypeptide consisting of 42 amino acids. The aggregation of this peptide – which induces neuronal apoptosis - is preceded by changes in the secondary and tertiary structures, which can be followed by CD spectroscopy. With the aid of combined CD and FTIR spectroscopies the effect of different small peptides on the aggregation profile of Aβ(1-42) is studied.
• Complex-formation between antisense oligonucleotides (AON) and cell-penetrating peptides (CPP). The application of AONs modulating gene expression is a promising approach in medicinal therapeutics. The method is based on the delivery of AON into the cells by peptides capable of translocation through the cell membrane. The major limitation of the technique is the low efficiency of membrane translocation and targeting. Hence, the main purpose of our work in this field is screening for CPPs which are highly effective in membrane translocation and targeting. Complex formation between CPP and AON can be followed by CD, FTIR spectroscopies and atomic force microscopy and the CPP/AON molar ratio optimal for cell penetration also can be estimated.
• Secondary and tertiary structures of different hydrophilic enzymes. There is growing interest in the use of enzymes in aqueous organic solutions. As compared with other catalysts, enzymes are stereoselective. Non-aqueous enzymology is of particular relevance when the desired reactants are poorly soluble in aqueous solution and when the reversal of a hydrolytic reaction is desired. The enzymes are able to catalyze reactions in organic solvents at low water content; however, they are less stable than in water. There is a direct relationship between the stability and the conformation of enzymes. Therefore we investigate the effect of organic solvents and stabilizers on the secondary and tertiary structures of various enzymes such as trypsin, chymotrypsin, papain, pepsin, etc.